The Hydra-Matic, GM’s first fully automatic transmission, was a great success, inspiring a host of rivals — including some within General Motors itself. In this installment of Ate Up With Motor, we look at the origins of Dynaflow and Powerglide, the ambitious but ill-fated Turboglide and Flight Pitch Dynaflow (a.k.a. Triple Turbine), the later Controlled Coupling Hydra-Matic and Roto Hydra-Matic, and more.

AUTHOR’S NOTE: This article, originally written in 2010, has been extensively revised and expanded for 2016.

IMPORTANT ADDITIONAL NOTE

I say this often, but on an article like this, it bears repeating in boldface type: I CANNOT to tell you how to fix any of these transmissions. I DO NOT sell (or buy) parts and I can’t help you find parts for them! If you have maintenance or repair questions, I strongly recommend that you seek out a factory service manual and/or consult a transmission specialist familiar with early automatics.

TORQUE CONVERTER DRIVE

As we saw in our first installment, the original Hydra-Matic, introduced in late 1939, was the world’s first really successful fully automatic transmission. By 1952, General Motors’ Detroit Transmission Division had produced more than 2 million Hydra-Matics, which were used by Oldsmobile, Cadillac, Pontiac, and a variety of outside automakers, ranging from Kaiser-Frazer to Muntz. Hydra-Matic was standard on all Cadillacs by the early fifties and went into most Oldsmobiles and more than 80% of Pontiacs.

Notably absent from the list of Hydra-Matic users were GM’s other automotive divisions, Buick and Chevrolet. Instead, between 1948 and 1963, those divisions fielded no fewer than seven distinctly different automatic transmissions, none of them related to the original Hydra-Matic or its successors, which we’ll discuss in more detail later in this article. (Starting in 1954, Chevrolet did offer Hydra-Matic on Series 3100, 3600, and 3800 trucks, but not on passenger cars.) Moreover, Buick and Chevrolet did not use the same transmissions, although their respective designs were conceptually similar in many respects.

This curious divergence may perplex the modern reader accustomed to a world of corporate engines and transmissions, even at GM. At almost any other automaker, then or now, Hydra-Matic (in various light-, medium-, and heavy-duty versions) would have been the automatic transmission until being phased out in favor of something newer and/or better. Even more surprising is the fact that the original impetus for Buick and Chevrolet’s unique automatic transmissions came not from the engineering staffs of those divisions (which in that era still enjoyed considerable autonomy), but rather from one of the principal architects of Hydra-Matic.

Engineer Oliver K. Kelley (often known as “O.K.” Kelley) began his career as an engineer at Cadillac in the late twenties and later worked for GM’s Yellow Truck and Coach Manufacturing subsidiary before joining Earl Thompson’s transmission development group, which by then had become part of the central Engineering Staff. Although Hydra-Matic was a team effort building on ideas Thompson had been developing since 1932, the three patents that most closely reflect the early production versions of the Hydra-Matic transmission were actually in Kelley’s name. When preproduction of the initial Model 180 Hydra-Matic began in mid-1939, Kelley was among the corporate engineers reassigned to Detroit Transmission Division (of which Kelley’s colleague William L. Carnegie became the first chief engineer) to oversee the transition from prototype to mass production.

We may presume, therefore, that Kelley was as familiar as anyone was with the original’s Hydra-Matic’s strengths and various limitations. As we’ve previously discussed, Hydra-Matic was very clever in many respects, but it was by no means a light, compact, or mechanically elegant design and it can’t have been cheap to manufacture. Furthermore, its operation was far from seamless even under the best of conditions, something that would earn the transmission considerable criticism in the years to come. There was obvious room for improvement.

Nonetheless, considering how much money GM had invested in the project, proposing, as Kelley and his colleague George R. Smith did in the summer of 1939, that the corporation begin working on another new and completely different automatic transmission was a bold suggestion indeed — particularly since at that point Hydra-Matic had not yet gone on sale. The most compelling point of Kelley and Smith’s argument, and the likely reason their proposal was not dismissed out of hand, was Hydra-Matic’s substantial production costs. While those might be acceptable for the senior divisions, which could pass the cost along to the customer, Hydra-Matic was expensive enough to be a questionable proposition for Chevrolet. Chevrolet owners were as weary as anyone of shifting gears (as evidenced by Chevrolet’s decision to make a vacuum-assisted shift linkage standard equipment for 1940), but whether the buyer of an $800 Chevy would be willing or able to spend $100 or more for a self-shifting transmission was another matter. The demand was there, but to tap it, Chevrolet would need an automatic transmission that could be priced to sell.

We don’t know what higher-level discussions Kelley and Smith’s proposal may have prompted, but the gist is not hard to guess. Even during the Depression, Chevrolet’s total sales volume had only once fallen below 400,000 units per year, and 1939 sales had been closer to 600,000. If Chevrolet could offer an automatic affordable enough to achieve a take-up of 50% or better, that would mean more than a quarter of a million transmissions a year. Since very few American drivers liked to shift, offering such a transmission would also give buyers a compelling reason to choose Chevrolet over low-priced rivals, so Chevrolet might even stand to increase its market share. With numbers like that, developing an automatic transmission for Chevrolet was likely to be a worthwhile investment even if it didn’t share a single bolt with Hydra-Matic.

The upshot was that Kelley and Smith’s rather daring proposal eventually paid off. In the summer of 1940, as first-year production of Hydra-Matic was winding down, they were transferred to the Engineering Staff as part of a reorganized transmission research team (known in contemporary GM vernacular as a product study group). This worked out particularly well for Kelley. Not only was he once again doing advanced research work — which we have to assume was vastly more interesting than production engineering — he was now leading the team, Earl Thompson having left General Motors about three months earlier.

The initial focus of Kelley’s new group was on torque converters. As Kelley was undoubtedly aware, some Yellow Truck & Coach buses had recently begun offering a Spicer torque converter transmission, a licensed derivative of the Lysholm-Smith unit developed by engineer Alf Lysholm of the Swedish firm Ljungstroms Angturbin AB. Over the previous decade, that transmission and others like it had become increasingly common for bus and railroad use, although to our knowledge, there had not yet been any production automotive applications.

Today, we’re accustomed to thinking of torque converters primarily as clutches, but a torque converter is also a type of infinitely variable transmission. (See the next page for a further explanation.) The bus and rail-car torque converter transmissions of the thirties used the converter primarily as a transmission, sometimes adding a separate clutch to connect the converter to the engine; conventional reduction gears were typically used only for reverse. Such transmissions were capable of providing torque multiplication comparable to Hydra-Matic with no perceptible steps and no need for a complicated hydraulic control mechanism, making them a potentially attractive Hydra-Matic alternative for Chevrolet.

Before Kelley and company had had the time for more than preliminary research, however, outside circumstances shifted their attention to a very different application.

M18 HELLCAT

In June 1940, about two months before the establishment of Kelley’s new product study group, GM president William S. Knudsen was summoned to Washington, D.C., where he was asked to oversee the ramp-up of American military production. By then, Europe had been at war for months, a growing number of European nations had fallen to the Nazis, and Great Britain’s position was looking increasingly precarious. Knudsen’s assignment was to enlist domestic industry in the accelerating U.S. rearmament effort.

Late that year, Kelley’s group was asked to shift their attention from a potential Chevrolet automatic to the development of a transmission that could take the place of the conventional gearboxes then used in most U.S. armored fighting vehicles (AFVs). The idea of automatic transmissions for tanks may sound faintly ridiculous, but what is merely annoying in a car — e.g., the need to shift gears — can be positively hazardous for a combat vehicle, particularly a lightly armored one. While Cadillac would shortly adopt Hydra-Matic for use in light tanks (mated, as we explained in Part 1 of this article, to Cadillac V-8 engines), Hydra-Matic had neither the torque multiplication nor the torque capacity needed for heavier AFVs.

Kelley and his team responded to this request by devising a heavy-duty semiautomatic torque converter transmission that was subsequently produced by Allison (then a GM division) under the trademark Torqmatic. The original Torqmatic 900T AFV transmission combined a six-element torque converter (a single impeller, three turbines, and two stators) with two hydraulically controlled planetary gearsets, providing three forward speeds and one reverse. The transmission still had to be shifted manually, but there was no need to de-clutch and little danger of missing a shift. Moreover, the torque converter alone provided a stall ratio of 4.8:1, so a useful amount of torque multiplication was available even in the direct-drive third gear.

This transmission was selected for the Buick-developed T-70 tank destroyer, which entered service in 1943 as the M18 Hellcat. The 900T helped to keep the M18’s nine-cylinder air-cooled Continental radial engine within its narrow power band all the way up to the Hellcat’s 50+ mph (80+ km/h) top speed and had the torque capacity to withstand the 972 cu. in. (15,972 cc) engine’s monstrous 940 lb-ft (1,275 N-m) net torque output, which would have made an oily metal milkshake of the Hydra-Matic’s innards. The transmission performed well in the M18 and later in the derivative M39 armored utility vehicle and the M26 Pershing medium tank, both introduced in 1944.

It was obvious early on that the torque converter transmission would also be well-suited to heavy civilian vehicles and equipment. After the war, Allison developed Torqmatic into an extensive and long-running line of heavy-duty torque converter transmissions for different military, commercial, and industrial applications, including trucks, buses, and heavy machinery. (Today, Torqmatic remains a trademark of Allison Transmission, which is no longer owned by General Motors.)

BUICK DYNAFLOW

While military work remained the top priority for Kelley and his team (and the auto industry in general) until late in the war, they had not forgotten their original objective. In late 1944, Kelley filed a patent application (U.S. Patent No. 2,606,460) for an automotive torque converter transmission combining a simple planetary gearset with a novel five-element torque converter featuring dual stators and dual impellers. The large primary impeller was driven directly by the engine. The much smaller secondary impeller, which was positioned between the stators and the inlet of the primary impeller, was connected to its larger sibling by an overrunning clutch.

The purpose of this unusual arrangement was to create the equivalent of a single impeller with two distinctly different blade profiles. The primary impeller was optimized for near-stall conditions (i.e., the period of highest torque multiplication, when the turbine was moving very slowly or not all). During that period, the primary impeller acted alone while the small secondary impeller freewheeled idly on its overrunning clutch. The secondary impeller initially spun much faster than the engine, but secondary impeller speed decreased as turbine speed increased. Once the two impellers were turning at the same speed, the overrunning clutch locked them together. The blades of the secondary impeller then acted as extensions of the first, effectively optimizing them for cruising efficiency.

By mid-1945, Kelley’s group had installed working prototypes of this transmission in several test mules. Although the torque converter transmission had been conceived with Chevrolet in mind, Kelley also showed off the prototypes to engineers at the other automotive divisions to see if any of them were interested in the new design as a potential alternative to Hydra-Matic.

The strongest interest came from Buick chief engineer Charles A. Chayne. Buick had been very resistant to the earlier Automatic Safety Transmission and had declined to adopt Hydra-Matic, which Chayne caustically nicknamed “Hydra-Jerk.” Some of Buick’s antipathy toward Hydra-Matic was probably attributable to divisional pride; some years earlier, the division had spent a lot of time and money on the abortive “Roller,” an infinitely variable friction drive transmission that Buick general manager Harlow Curtice had been obliged to cancel back in 1934. Nonetheless, the concerns about shift harshness were probably not without merit. Unlike Oldsmobile, Cadillac, and Pontiac, which used open driveshafts, Buick (and Chevrolet) in those days used torque tube drive, which combined the enclosed driveshaft and rear axle into a single rigid assembly connected to the transmission via a single U-joint. Since the primary purpose of the torque tube was to transmit drive torque, the mass of the axle assembly would have amplified each of Hydra-Matic’s firm shifts into an uncouth thump, hardly in keeping with Buick’s upscale image.

Chayne and Curtice both sampled the prototype torque converter automatic and found it much more to their liking. It was mechanically straightforward and offered seamless if rather stately acceleration. Chayne subsequently assigned Buick’s own engineers to collaborate with Kelley’s team on the development of a production version of the torque converter transmission for Buick.

After much development and extensive testing, the new transmission, which Buick christened Dynaflow, was finally announced in January 1948. It went on sale in March as an option for the top-of-the-line Buick Roadmaster. While Dynaflow was mechanically simpler and somewhat lighter than Hydra-Matic, the Buick transmission was no cheaper — initial list price was $206 (more than $2,000 in 2016 dollars), some $20–$30 more than the contemporary Hydra-Matic.

Dynaflow retained the five-element, dual-impeller torque converter of the early prototypes, but the planetary transmission adopted what today is commonly known as a Ravigneaux gearset (after French inventor Pol Ravigneaux, who patented many variations of this layout in the thirties and forties). This comprised two sun gears, six planet gears (three short, three long) on a single planet carrier, and a single annulus (ring gear). The front sun gear was affixed to a brake drum and a multi-disc direct drive clutch. The input shaft from the torque converter turbine passed through the center of the front sun gear (which had a hollow center for that purpose) to drive the rear sun gear. The annulus formed a second brake drum surrounding the sun and planet gears, whose carrier was affixed to the output shaft.

Each of the two drums was surrounded by a contracting band brake. Engaging only the front brake (the low band) would put the gearset in reduction while engaging only the rear brake (the reverse band) provided reverse reduction; gear ratios were +/-1.82:1 respectively. Releasing both brakes and engaging the direct drive clutch locked the input shaft to the front brake drum so that both sun gears (and thus the entire gearset) would rotate together at the same speed as the torque converter turbine. Releasing the direct drive clutch as well as both bands put the transmission in neutral, allowing the gears to turn idly. A mechanical pawl allowed the output shaft to be locked in place to serve as a parking brake; unlike the early Hydra-Matic, there was a separate position for this on the shift quadrant. Other notable Dynaflow features that Hydra-Matic lacked were an oil cooler (in this era used only on heavy-duty Hydra-Matics) and a pair of hydraulic accumulators to damp the shock of clutch or band engagements.

The original Dynaflow is often described as a two-speed automatic, but the only automatic “shifting” the transmission provided was via the torque converter. Like Hydra-Matic, Dynaflow had front and rear oil pumps supplying operating pressure to control the transmission’s clutch, bands, and parking pawl. Unlike its corporate cousin, however, Dynaflow had neither a hydraulic speed governor nor a throttle valve, relying entirely on the position of the selector lever to direct the flow of oil to the appropriate elements for each range. With the selector in Drive, the direct drive clutch remained engaged at all speeds. The driver could manually select Low, which released the clutch and engaged the low band, but the transmission would then remain in that gear until the selector was moved to a different range. This was by design; while it wouldn’t have been difficult to engineer the transmission to start in its reduction gear and shift automatically to and from direct drive, Kelley’s team and their counterparts at Buick wanted normal operation to be as ‘stepless’ as possible.

The tradeoff was performance. While non-automotive torque converters often had stall ratios of 4.00:1 or more, those units were intended for use with heavy-duty engines that spent much of their operating lives at or near full throttle. To provide torque characteristics more suitable for an automotive engine — and to avoid excessive slippage at cruising speeds — the early Dynaflow converter had a stall ratio of only 2.25:1. That was taller (numerically lower) than second gear of a contemporary Hydra-Matic and significantly taller than the 2.67:1 low gear of Buick’s standard three-speed manual transmission.

In partial compensation, Dynaflow-equipped Roadmasters used a special high-compression version of Buick’s 320 cu. in. (5,247 cc) straight eight that added an extra 6 hp (4 kW) and 4 lb-ft (5 N-m) of torque. Even so, Dynaflow’s off-the-line response was lethargic unless you manually selected Low, which could be done at any speed up to about 45 mph (72 km/h). Unfortunately, frequent manual gear changes exacerbated the already heavy fuel consumption and would eventually take their toll on the transmission’s low band and direct drive clutch, which were intended for only occasional use. Buick cautiously described Dynaflow’s reduction gear as “emergency low.”

Despite those shortcomings, Dynaflow was well-suited to the character of postwar Buicks, which emphasized unhurried plushness over performance or road manners. The average Buick buyer of the time was not terribly concerned with fuel economy and welcomed Dynaflow’s lazy smoothness. It was too bad that Buick no longer offered formal cars; Dynaflow lent itself admirably to a processional pace.

CHEVROLET POWERGLIDE

Although Buick had beaten Chevrolet to the punch, GM’s largest automotive division had also evaluated the corporate engineers’ torque converter transmission and begun work in 1946 on a production version for Chevrolet. Dubbed Powerglide, it finally debuted as a $159 option for 1950 Chevrolet DeLuxe models.

In its original form, Powerglide was much like the early Dynaflow — not surprising considering that both were production derivatives of the same basic corporate design. Both transmissions used a two-speed Ravigneaux gearset providing 1.82:1 low and reverse ratios. Both had a five-element torque converter with dual stators and dual impellers, although Powerglide’s stall ratio was slightly lower, at 2.20:1. Powerglide’s hydraulic control system also included a vacuum modulator that varied operating pressure based on the engine’s manifold air pressure, a feature Dynaflow didn’t have.

Powerglide’s principal novelty, developed and patented by Kelley and William S. Wolfram (U.S. Patent No. 2,651,918), was an unusual auxiliary fluid coupling, incorporated within the torque converter and sharing the same oil supply. The auxiliary coupling’s “impeller” was actually an additional set of vanes mounted on the turbine torus, a little inboard of the turbine inlet, while the “turbine” was a comparable set of vanes on the primary impeller. Each set of auxiliary vanes was curved in the opposite direction of the corresponding primary blades.

The auxiliary coupling was intended to address a minor but disconcerting flaw of most fluid clutches: a distinct shortage of engine braking when the speed of the output shaft exceeds the speed of the engine (technically known as overrun), such as when coasting or descending a hill with the throttle closed. Under those conditions, the output shaft of an early Powerglide-equipped car would turn the converter turbine, whose auxiliary vanes would transmit that motion to the auxiliary vanes on the primary impeller and attempt to overdrive the engine; the engine’s inertia would then provide a braking effect. The auxiliary coupling also allowed the car to be push-started at speeds as low as 12 mph (19 km/h). The downside was a bit of additional drag within the converter during normal acceleration.

In other respects, Powerglide operated very much like Dynaflow and suffered the same limitations. The performance penalty was even more pronounced with the Chevrolet six than with Buick’s big straight eight, particularly since Powerglide included a taller 3.55:1 axle ratio, compared to 4.11 for Chevrolets with manual shift. Despite the bigger, more powerful engine that was standard with Powerglide, Chevrolets with automatic were more than five seconds slower to 60 mph (97 km/h) than standard-shift cars (assuming a start in Drive) and returned less-than-frugal fuel economy.

Although these limitations did little to dampen buyer enthusiasm, Chevrolet quickly moved to address Powerglide’s performance shortfall with an extensive redesign of the transmission, introduced for the 1953 model year. The planetary transmission retained the same internal ratios as before, although the low band and clutch were beefed up. However, a completely redesigned hydraulic control system now started in reduction rather than direct drive and executed automatic upshifts and downshifts at speeds up to 42 mph (68 km/h). As in Hydra-Matic, shift points were determined by road speed and throttle position. At the same time, the five-element torque converter and its auxiliary coupling were discarded in favor of a simpler (and undoubtedly cheaper) three-element unit. The stall ratio was reduced slightly, to 2:10:1, but overall starting ratio in Drive was now 3.82:1.

This revised arrangement was a compromise of Kelley’s original vision, but it was much better suited to Chevrolet’s needs and worked well enough for most buyers. Chevrolet would later offer another “pure” torque converter automatic, the Turboglide (discussed in more detail later in this article), but Powerglide would remain the division’s principal transmission well into the sixties.

There were of course a number of design changes along the way. Torque capacity had to be increased several times to cope with progressively larger and more powerful engines. For 1958, Powerglide also got a revised hydraulic system with a new PRNDL shift pattern, reducing the potential confusion for drivers switching between Powerglide-equipped cars and ones with Turboglide, which already used the latter pattern.

For 1960, Chevrolet engineers adapted Powerglide components to create a lightweight automatic transaxle for the rear-engine Corvair. The torque converter of the Corvair Powerglide was mounted at the back of the transaxle, behind the rear axle line, while the planetary gearbox was ahead of the axle. A narrow central shaft passing through the center of the differential pinion allowed the engine to drive the transaxle’s front oil pump. Around the oil pump driveshaft was the main shaft, connecting the torque converter turbine to the planetary gearbox. The output shaft was a hollow sleeve surrounding the main shaft, connecting the gearset’s planet carrier to the differential gears. The Ravigneaux gearset itself was similar to that of the standard Powerglide and shared the same +/-1.82 indirect ratios, but traded the reverse band brake for a multi-disc reverse clutch that performed the same function. The standard Powerglide’s parking pawl was omitted in the interests of cost reduction, but the Corvair unit got a lighter aluminum case and a higher, 2.60:1 stall ratio, providing the lightweight Corvair with surprisingly peppy performance.

For the 1962 model year, Chevrolet introduced new light-duty and heavy-duty versions of the conventional Powerglide, now also using an aluminum case and adopting a Corvair-style multi-disc reverse clutch. The light-duty unit, used in the compact Chevy II, retained the +/-1.82 ratios, but the heavy-duty unit had a revised gearset with indirect ratios of +/-1.76. The “standard” medium-duty Powerglide used in most full-size Chevrolets adopted most of these changes and the aluminum case for 1963. In this form, and with various further refinements, Powerglide remained in use on various North American models through the 1973 model year.

In 1968, Chevrolet revived the original Powerglide concept with Torque-Drive, a torque converter transmission with a two-speed Ravigneaux gearset and a simple hydraulic control system that included no provision for automatic gear changes. Although similar in operation to the original 1950–1952 Powerglide, Torque-Drive had an aluminum case and three-element torque converter like its latter-day brethren. By sixties standards, Torque-Drive — which Chevrolet now described as semiautomatic — was rather quaint, although its mechanical simplicity enabled Chevrolet to sell it for as little as $68.65, over $100 less than the fully automatic Powerglide. Torque-Drive was available on six-cylinder Camaros through 1970, on the four- and six-cylinder Chevy II and Nova into 1971, and on the first-year Chevrolet Vega.

TWIN-TURBINE DYNAFLOW

The 1953 model year also saw the introduction of a heavily revised Buick automatic, dubbed Twin-Turbine Dynaflow. Developed by a group of Buick engineers led by Rudolf J. Gorsky, the twin-turbine transmission was again based on concepts originated in O.K. Kelley’s corporate engineering team; most of the underlying patents (in particular U.S. Patents 2,766,641; 2,782,659; and 3,025,720) were in Kelley’s name. The apparent objectives of the new transmission were to provide additional torque multiplication without hurting part-throttle fuel economy, raising the converter stall speed, or compromising the outstanding smoothness that had always been Dynaflow’s principal virtue.

Twin-Turbine Dynaflow retained the original Dynaflow’s Ravigneaux gearbox, but the torque converter was a new four-element design with a single impeller, a single stator, and — as the name implied — two turbines. The first turbine, which faced the impeller, was essentially a metal ring with closely spaced, slot-like radial vanes around its rim. That ring was pressed into a drum-like support shell, within which was the second turbine, a more conventional bladed torus. The stator, which sat within the first turbine ring, was positioned to receive the ‘backwash’ of oil exiting the second turbine.

Within the turbines’ central hub was an additional planetary gearset. (Insofar as the torque converter and gearbox were separate entities, this gearset was part of the converter.) The annulus of the converter gearset was driven by the first turbine support shell. The gearset’s planet carrier was attached at one end to the second turbine and at the other to the gearbox input shaft. The converter gearset sun gear, meanwhile, was connected to the hub of the stator and shared its one-way clutch. Reverse torque on either element would lock both elements, putting the converter gearset in reduction. This multiplied any torque applied to the first turbine by a ratio of 1.60:1 and forced the second turbine to rotate at 62.5% percent of the speed of the first turbine (i.e., first turbine speed divided by 1.6).

The stream of oil from the impeller would first enter the first turbine, where the oil attempted to impart its angular velocity — that is, to apply torque — to the turbine vanes. Thanks to our old pal, Newton’s Third Law of Motion, whatever torque the oil stream exerted on the turbine vanes would apply an equal and opposite reaction torque on the oil. Since the vanes of the first turbine were open at the back, oil passing through them retained its forward momentum, but the reaction torque effectively reduced the oil’s angular velocity. Oil exiting the first turbine would then enter the inlet of the second turbine, pass through its vanes to the turbine outlet, and then curve back through the stator blades to the impeller.

Up to the point of stall (that is, as long as neither turbine was moving), the oil stream would apply all or nearly all of its torque to the vanes of the first turbine. Consequently, at stall and for a brief period thereafter, the vanes of the first turbine exerted so much reaction torque on the oil stream that the oil exited the first turbine spinning in the opposite direction and therefore opposed the rotation of the second turbine, slightly reducing the net torque on the gearbox input shaft.

Once the first turbine began to move, the oil stream exerted progressively less torque on the first turbine’s vanes, which in essence were now trying to run away from the spinning oil stream. (This is a gross simplification of some rather complicated vector math, but we figure you’re probably confused enough already.) The reduced torque on the first turbine’s vanes meant the vanes also exerted progressively less reaction torque on the oil, allowing the oil stream to enter the second turbine with a somewhat reduced but still positive angular velocity (that is, spinning in the same direction as the impeller) and exert a steadily increasing positive torque on the second turbine’s vanes. To put it another way, discounting slippage, any impeller torque not applied to the first turbine would be applied to the second. Again, torque on the first turbine was multiplied by the planetary gears; torque on the second turbine was not.

As long as the sun gear clutch remained locked, the planetary gearset forced the two turbines to maintain a fixed speed ratio. Therefore, the second turbine could not turn faster (or slower) than 62.5% of the first turbine’s speed. Once the rotational speed of the first turbine was close to impeller speed, however, there was enough torque on the second turbine to cause it, and thus the planet carrier, to overdrive the annulus and the first turbine rather than being driven by them in reduction. That unlocked the sun gear/stator clutch (causing all torque multiplication to cease) and allowed the stator, the sun gear, the annulus, and the first turbine to freewheel idly; the first turbine was now turning fast enough that the oil stream could no longer exert a meaningful amount of torque on the turbine vanes. The torque applied to the second turbine, meanwhile, caused the second turbine (and thus the carrier and the gearbox input shaft) to continue accelerating until it was rotating at close to engine speed.

Like any torque converter, the torque multiplication provided by the dual-turbine converter was continuously variable, peaking at stall and gradually diminishing with increasing turbine speeds. However, there was now significantly more area under the curve thanks to the converter gearset’s additional mechanical advantage. Despite the initial interference between the turbines, which hurt the converter’s efficiency at stall, the converter gearset allowed a higher net stall ratio — now 2.45:1 — and somewhat lower stall speeds. The use of two separate turbines also allowed each to be optimized for its respective operating regime, providing more efficient cruising for better fuel economy without sacrificing off-the-line performance.

Twin-Turbine Dynaflow’s principal shortcomings were engine braking and passing response. Even with the converter gearset, there was still little engine braking in Drive; the sun gear clutch would automatically unlock if the output shaft overran the engine. The converter gearset was also of marginal usefulness for passing unless turbine speeds fell significantly below engine speed. Shifting to Low range mitigated both these issues, but Low was really too short to be ideal for passing or mountain driving at highway speeds. Dual-Range Hydra-Matic was much more convenient in those situations.

Buick attempted to address that limitation with the 1955 introduction of Variable Pitch Dynaflow. The revised transmission retained the four-element torque converter and converter gearset, but added Kelley’s latest brainstorm (described in U.S. Patent No. 2,999,400): a variable-pitch feature for the stator blades, similar in principle to a variable-pitch propeller. Rather than being affixed to the stator hub in the usual manner, the stator blades were connected via a series of small crank pins to a servo-controlled annular piston (basically a flat metal ring) that could pivot forward or backward, thus rotating each blade on its crank. Hydraulic pressure on the piston normally held the blades at a low angle relative to the oil stream. Flooring the accelerator, or moving the selector to Low or Reverse, opened a control valve to exhaust one side of the stator servo, flipping the piston to its forward position and cranking the stator blades to a more upright angle. Backing off on the throttle would reengage the servo, causing the piston to flip back to its normal position and thus crank the stator blades back to low angle.

With the blades at their low-angle position, the converter traded some torque multiplication — net stall ratio in low was 2.10:1 — for nominal stall speeds as low as 1,400 rpm, reduced throttle lag, and greater efficiency at cruising speeds. Shifting the stator blades to high angle brought the net stall ratio to 2.50:1 and raised the stall speed to a nominal 2,600 rpm for stronger off-the-line performance and better passing response. Changing the stator pitch in this way wasn’t as effective as an additional reduction gear, but it was helpful nonetheless. The principal drawback was that at very high road speeds, forcing the stator blades to high angle would hurt performance more than it helped.

To take fuller advantage of the new stator, the converter gearset sun gear was divorced from the stator hub and given its own sprag clutch, separate from the stator’s cam-and-roller one-way clutch. Having its own clutch allowed the stator to remain locked after the first turbine freewheeled (further fattening the torque multiplication curve) or to re-lock in response to load without necessarily putting the converter gearset back in reduction.

Although Variable Pitch Dynaflow provided slightly better performance and somewhat better fuel economy than the earlier Twin-Turbine Dynaflow, an effective starting ratio of no more than 2.50:1 in Drive was still marginal for the steadily increasing curb weights (and steadily decreasing axle ratios) of mid-fifties Buicks. This was addressed for 1956 with a revised five-element torque converter that incorporated dual stators as well as twin turbines.

The additional stator — confusingly described as the first stator or front stator — was mounted immediately behind the first turbine and looked much like it. However, the stator blades were angled in more or less the opposite direction so as to counteract the reverse torque that had previously compromised the twin-turbine converter’s efficiency near stall speed. Now, oil entering the second turbine at stall increased the torque on the turbine vanes and the planet carrier rather than opposing their rotation. To put it another way, with the turbines stationary or turning slowly, the rotary flow in different points of the converter was now like this:

• From the impeller outlet to the first turbine inlet: with the engine
• From the first turbine outlet to the first stator: opposite the engine
• From the first stator to the second turbine inlet: with the engine
• From the second turbine outlet to the variable-pitch stator: opposite the engine
• From the variable-pitch stator to the impeller inlet: with the engine.

Once the first turbine was turning fast enough that the rotary flow of oil out of the first turbine outlet was no longer opposite the engine’s rotation, the first stator would freewheel on its own sprag clutch.

The variable-pitch stator and converter gearset were retained, but the additional stator increased the converter’s net stall ratio to 3.10:1 at a nominal 1,500 rpm with the variable-pitch stator blades in their low-angle position, or 3.50:1 at 2,800 rpm in high position. The variable-pitch stator controls were also modified so that the blades would normally remain at low angle in Low or Reverse rather than automatically switching to high angle in either of those gears.

Even the high-angle stall ratio didn’t quite match the first-gear ratio of the four-speed Hydra-Matic or the step-off ratios of contemporary two-speed torque converter automatics, but the additional torque multiplication made Dynaflow-equipped cars a good deal less sleepy when starting in Drive. More importantly, as far as Buick was concerned, that improved performance was still obtained without any perceptible shift points.

Variable Pitch Dynaflow — renamed Twin Turbine for 1959 and Turbine Drive for 1960 — received a variety of further refinements, including several revisions to the stator blade pitch (making the stall ratios 3.10:1 and 3.40:1); marginally higher stall speeds; and, from 1961 on, a shorter, slightly lighter case. Turbine Drive was the sole transmission offered on full-size Buicks from 1961 through 1963.

CONTROLLED COUPLING HYDRA-MATIC

Despite the ongoing development of Powerglide and Dynaflow, GM had no intention of abandoning Hydra-Matic, which was still used in substantial numbers by Pontiac, Oldsmobile, Cadillac, and several outside automakers. Aside from GM’s substantial capital investment in tooling and factory space, which the corporation wasn’t about to casually discard, the various users (and many of their customers) had strong feelings about the comparative advantages of Hydra-Matic and its assorted rivals.

In 1952, the Detroit Transmission Division embarked on a $35 million revamp of the four-speed Dual-Range Hydra-Matic. Walter B. Herndon, one of the engineers from Earl Thompson’s original transmission development group, filed a patent covering most of the fundamentals of the redesigned transmission (U.S. Patent No. 2,876,656) in November 1953, with most of the rest covered in a subsequent application by August H. Borman Jr., Forrest R. Cheek, and Milton H. Scheiter in December 1954 (U.S. Patent No. 3,048,055), but the second-generation Hydra-Matic didn’t actually go on sale until the 1956 model year. (We assume the destruction of the Hydra-Matic plant in Livonia in August 1953 was at least partly responsible for the delay.) Development of the production version, formally known as the Model 315 or Controlled Coupling Hydra-Matic, was credited to Detroit Transmission engineers P.J. Rhoads and Kenneth W. Gage; Gage subsequently moved to Buick, where he worked on later iterations of Dynaflow.

To understand the changes to the second-generation Hydra-Matic (called “Jetaway Hydra-Matic” by Oldsmobile, “Strato-Flight Hydra-Matic” and later “Super Hydra-Matic” by Pontiac), it’s helpful to first recap the major elements of the original version. As we’ve previously explained, the early Hydra-Matic had a single fluid coupling and three planetary gearsets controlled using two contracting band-type brakes, two multi-disc clutch packs, and (from 1951 on) a single cone clutch to provide four forward speeds and one reverse. The fluid coupling itself was driven indirectly: The torus cover, which was bolted to the engine flywheel, drove the annulus of the first planetary gearset, whose planet carrier drove a hollow intermediate shaft (surrounding and concentric with the transmission main shaft) that connected the fluid coupling impeller to the clutch assembly of the second gearset (which also partially bypassed the fluid coupling in third and fourth in order to reduce slippage). The fluid coupling’s turbine drove the transmission main shaft and the sun gear(s) of the second planetary gearset.

The following table shows the gear and band engagements for the 1952–1954 Dual-Range Hydra-Matic. (As noted in Part 1, earlier units had the same engagement sequence, but different ratios and (through 1950) used a pawl rather than a cone clutch for reverse. Some users retained the above ratios for 1955, but others (including Cadillac and Pontiac) adopted a revised front gearset with a ratio of 1.55:1, which made first gear 4.10:1.) In this table, “REL” and “ENG” abbreviate “RELEASED” and “ENGAGED” respectively.

The redesigned Hydra-Matic maintained the same general layout (although some components were repositioned), but replaced the front clutch pack with a second fluid coupling — the eponymous controlled coupling — located immediately behind the torus housing, between the first and second planetary gearsets. The second coupling was smaller than the main coupling and incorporated valves that allowed its oil supply to be completely drained or completely refilled in less than half a second. The rear clutch remained a multi-disc unit, although it was beefed up for greater torque capacity. (The design team considered adding a third fluid coupling to replace the rear clutch, but ultimately decided the benefits weren’t worth the substantial extra cost.)

The second fluid coupling had the same function as the multi-disc clutch it replaced: to put the front planetary gearset in direct drive by causing the annulus, the sun gear, and the planet carrier to rotate together at the same speed, or close to it. The main coupling torus cover drove both the front unit annulus and the impeller of the second coupling through its torus cover, which also drove the front oil pump. The second coupling’s turbine was connected (via a hollow sleeve shaft) to the front unit sun gear. If the coupling was empty, the impeller simply turned idly and the turbine remained stationary. Refilling the coupling would cause the impeller to drive the turbine — and thus the sun gear — at close to engine speed. (In technical terms, filling the second coupling split the engine’s torque between the annulus, which was driven mechanically, and the sun gear, which was driven hydraulically. The torque was then recombined by the planet carrier.)

The redesigned transmission also deleted the earlier Hydra-Matic’s front brake band, replacing it with a sprag-type one-way clutch that performed the same function: holding the front gearset sun gear in place whenever the front clutch was disengaged (or in this case empty). A similar sprag clutch was attached to the annulus of the second planetary gearset. Since the sprag clutches didn’t require any external engagement mechanisms, automatic shifts up or down could now be accomplished by controlling the front coupling and the rear clutch (as shown in the table below) rather than simultaneously coordinating clutch and brake engagements. The sprags also needed no routine adjustment.

The use of the sprag clutches necessitated an alternative means of obtaining neutral and reverse, which both required that the rear annulus be able to turn backward in some circumstances. In the earlier single-coupling Hydra-Matic, that was achieved by simultaneously releasing the rear clutch and the rear brake band, but the new transmission’s rear sprag clutch couldn’t be disengaged that way. Instead, the Controlled Coupling Hydra-Matic interposed a multi-disc neutral clutch between the rear sprag’s outer race and the transmission case. The neutral clutch was engaged in all forward gears, allowing the rear sprag to function normally. In neutral or reverse, with the neutral clutch disengaged, the sprags wouldn’t lock even if turned backward; reaction torque would just cause the neutral clutch hub to rotate backward along with the rear annulus. The front sprag, which had no such mechanism, remained locked in both neutral and reverse as long as the engine was running.

Hydraulic controls were similar in basic principle to those of the earlier Dual-Range Hydra-Matic, but the system was redesigned to include drain/fill valves for the front coupling and servo controls for the neutral clutch, overrun band, and overrun clutch.

Another complication of the sprag clutches was that they would release on the overrun, so second or third gears provided no more engine braking than fourth and the transmission would freewheel when coasting in first. To compensate, the Controlled Coupling Hydra-Matic retained the rear brake band — now called the overrun band — and added a single-disc overrun clutch that could be engaged to lock the front unit sun gear sleeve shaft. The overrun clutch and overrun band served as auxiliary brakes, supplementing the sprag clutches in Low and D3 (aka S or D-Right) ranges. (The overrun clutch was also locked in reverse.) Neither the overrun clutch nor the overrun band was operative in D4 (aka D or D-Left) range, so there still wasn’t much engine braking in that range. Given the limitations of contemporary drum brakes, selecting D3 or Low for mountain driving or maneuvering on steep grades was prudent.

The following table summarizes the shift sequence for the Controlled Coupling Hydra-Matic. (Again, “REL” is short for “RELEASED” and “ENG” is short for “ENGAGED,” both abbreviated in the interests of space.)

The redesigned Hydra-Matic now had a Park position on the selector, a first for the Hydra-Matic series. The parking pawl that position controlled wasn’t entirely new: Hydra-Matic had always incorporated a pawl to lock the annulus of the third planetary gearset, originally to provide reduction in reverse and, after the reverse cone clutch was added for 1951, later for use as a parking brake. The parking pawl on the Controlled Coupling Hydra-Matic now acted on the reverse planetary gearset’s planet carrier rather than the annulus and could be used in addition to or instead of a conventional emergency brake acting on the rear drums.

Since both fluid couplings were active in fourth gear, the Controlled Coupling Hydra-Matic also slipped a bit more at cruising speed than did its single-coupling predecessor. The torque split in third and fourth gears mitigated that somewhat, but the redesigned transmission nonetheless sacrificed some fuel efficiency. Interestingly, Herndon’s 1953 patent disclosure included provision for a mechanical lockup clutch to completely eliminate the second coupling’s additional slippage in fourth gear, but that feature was absent from the production transmission.

The Controlled Coupling Hydra-Matic’s principal advantage was significantly smoother shifts than the single-coupling Hydra-Matic could muster. The rear clutch could still produce a mild thump on 2–3 or 3–2 shifts, but it was seldom objectionable and the 1–2 and 3–4 shifts were almost seamless. Shift quality was also more consistent than before — a distinct improvement over the single-coupling Hydra-Matic, which was very sensitive to proper adjustment of its bands and linkages. A bit of straight-line performance was inevitably sacrificed for that smoothness, but after 16 years of complaints about the endemic jerkiness of the single-coupling Hydra-Matic, that was a tradeoff many were prepared to accept.

Unfortunately, owners found that the new Hydra-Matic was somewhat less rugged than the single-coupling transmission it replaced. Particularly on early units, operation of the second coupling could be erratic in extreme temperatures, the aluminum torus cover was prone to cracks, and aggressive driving could damage the sprags of the one-way clutches. A litany of running changes progressively addressed most of those issues, but it’s interesting to note that GMC and Chevrolet trucks stuck with the older Dual-Range Hydra-Matic until the early sixties. (So did Rolls-Royce, which built the Dual-Range Hydra-Matic under license.)

The update also did nothing to reduce Hydra-Matic’s considerable weight, which now ran to some 225 to 240 lb (102 to 109 kg), or make it cheaper to build; it was undoubtedly one of the most costly, if not the costliest, of contemporary automatics. Consequently, there were fewer outside users than before. American Motors purchased some dual-coupling Hydra-Matics (which AMC dubbed “Flashaway”) for 1956–1957 Hudson and Nash models, but subsequently switched to less-expensive Borg-Warner (and later Chrysler) automatics. Even within GM, cost considerations would soon prompt Oldsmobile and Pontiac to adopt cheaper alternatives, although some Cadillac and Pontiac models would retain the Controlled Coupling Hydra-Matic through the 1964 model year.

TURBOGLIDE AND FLIGHT PITCH DYNAFLOW

With the introduction of the dual-stator Variable Pitch Dynaflow, GM’s “pure” torque converter automatic had reached an advanced state of development. However, Oliver Kelley’s corporate transmission group was not yet satisfied and kept working on what was supposed to be the ultimate torque converter automatic: a triple-turbine transmission.

To be clear, there were actually two such transmissions: Chevrolet’s Turboglide, introduced as an option on 1957 Chevrolets with the 283 cu. in. (4,638 cc) V8 engine, followed a year later by Buick’s Flight Pitch Dynaflow, which was standard on the 1958 Buick Roadmaster and Limited and optional on other models. Although Turboglide and Flight Pitch Dynaflow (renamed Triple Turbine for 1959) differed in layout and in many details, both transmissions were based on a common set of ideas developed by Kelly’s team and were, like the original Dynaflow and Powerglide, essentially variations of the same design.

The easiest way to conceptualize the triple-turbine transmission is as a Variable Pitch Dynaflow with an additional drive turbine rather than a second stator. The extra turbine was linked to its own set of planetary gears, the addition of which required moving both gearsets out of the converter hub and into the transmission case. Controlling those gearsets — which superseded Dynaflow’s familiar Ravigneaux gearbox — were no fewer than six clutches: two one-way clutches (not counting the stator clutch), a neutral clutch, a reverse clutch, a forward clutch, and a “hill retarder” or “grade retarder” clutch (the function of which we’ll explain shortly). Turboglide initially used cone-type neutral, reverse, and forward clutches with a multi-disc hill retarder clutch, but switched to a multi-disc neutral clutch for 1958 and adopted multi-disc reverse and forward clutches for 1959. Flight Pitch Dynaflow and Triple Turbine used only multi-disc clutches from the start.

The transmission’s two one-way clutches, which were linked to the reaction members of the two planetary gearsets — the front unit sun gear and rear unit annulus, as on Hydra-Matic — were cleverly interconnected, with the inner race of the front sun gear clutch forming the outer race of the rear annulus clutch. The forward clutch served to anchor both one-way clutches to the case, preventing either reaction member from turning backward. The rear annulus was free to rotate forward while the front sun gear remained locked, but the front sun gear could only turn forward if the rear annulus also did so. With the forward clutch released, reaction torque on the rear annulus would lock it against the front sun gear clutch, which caused both clutches to turn backward together, carrying their respective gears with them.

As in Twin-Turbine Dynaflow, the triple-turbine transmission’s first turbine was affixed to a support shell, within which were mounted the other two turbines. The support shell was splined to a central input shaft that caused the rear unit sun gear to rotate with the first turbine. The inner hub of the second turbine was attached to a hollow sleeve shaft that caused the second turbine and front unit annulus to rotate together. A third hollow shaft, located between the other two, connected the third turbine to the neutral clutch, which when engaged linked the third turbine to the planetary gearsets’ interconnected front and rear planet carriers. A flange at the trailing edge of the rear carrier allowed the carriers to drive the transmission output shaft.

The mechanics of the triple-turbine transmission were very similar to those of the twin-turbine units, but there were now three stages rather than two. At stall, most of the impeller’s torque (augmented as usual by the stator) was applied to the first turbine and thus the rear unit sun gear. This would exert reaction torque on the rear annulus, so if the forward clutch was engaged, both one-way clutches would lock, putting both gearsets in reduction. Oil exiting the first turbine would initially apply a small amount of positive torque to the second turbine and therefore to the front unit annulus. Once the turbines were moving, the oil stream exerted progressively less torque on the first turbine and progressively more on the vanes of the second. The torque exerted on each turbine was multiplied by their respective planetary gears and applied to the output shaft through the conjoined planet carriers. Turboglide’s gear ratios were 2.67:1 for the rear gearset and 1.60:1 for the front unit; the ratios for Flight Pitch Dynaflow/Triple Turbine were 2.86:1 and 1.55:1 respectively.

(We should emphasize here that while these transmissions technically had three geared ratios, they were NOT three-speed automatics. Over the years, some sources have incorrectly described them as such, which, while true in one sense, betrays a fundamental misunderstanding of how these transmissions actually function.)

If you followed our explanation of Twin-Turbine and Variable Pitch Dynaflow earlier in this article, you may recall that in the single-stator versions of those transmissions, oil flow from the first turbine would initially oppose the rotation of the second, a problem rectified on later versions of Variable Pitch Dynaflow by the addition of the front stator. Since the triple-turbine transmissions lacked the additional stator, oil exiting the first and second turbines at or just above stall would similarly oppose the rotation of the third turbine, reducing the net torque on the output shaft. As torque shifted from the first turbine to the second, the oil flow from the second turbine began to exert positive torque on the third turbine. (The more aggressive the initial launch, the longer this took.)

Once the speed of the second turbine reached approximately 55–60% of the speed of the first turbine (the exact transition point depending on the comparative ratios of the front and rear gearsets), the front unit annulus would attempt to rotate its planet carrier faster than the rear carrier. Since the two carriers were connected, the rear carrier was obliged to rotate faster as well. This caused the carrier to overdrive the rear unit sun gear and the first turbine, which removed the reaction torque on the rear unit annulus and its one-way clutch. The first turbine would then freewheel idly, leaving the other two turbines to drive the output shaft. The second and third turbine would repeat this process once there was enough torque on the third turbine to drive it at more than about 60% of the speed of the second (again depending on the exact ratio of the front gearset), which left both the first and second turbines spinning idly. The stator continued to provide some torque multiplication until toroidal flow dropped off enough to release the stator’s one-way clutch.

Both Turboglide and Flight Pitch Dynaflow/Triple Turbine used variable-pitch stators, but of different designs. Turboglide had a two-position stator very similar to the one used in 1957 and later Variable Pitch Dynaflow/Twin Turbine transmissions, but Buick adopted a more sophisticated infinitely variable stator. As with the two-position unit, stator blade angle was controlled by the pivoting of an annular piston controlled by hydraulic pressure. However, rather than simply flipping back and forth between two discrete positions, the infinitely variable stator’s control piston was balanced between opposing converter and throttle valve pressures that could hold the piston at any position within its range of motion. In this way, the stator blades could continuously adjust their pitch based on load. A “kickdown” valve opened by flooring the accelerator would still force the blades to their highest possible angle, just as with the two-position stator.

Reverse was an adaptation of the principle used in contemporary Hydra-Matics: allowing reaction torque on the reaction member of the rear gearset to provide reverse rotation and then compounding it with another gearset to provide reverse reduction. Since there were only two gearsets rather than three, the front unit now performed the latter chore. To accomplish all this, the neutral and reverse clutches were engaged, connecting the third turbine to the planet carriers and holding the front unit annulus in place, while the forward clutch was released so that the one-way clutches were no longer anchored to the case. The rotation of the first turbine (and thus the rear unit sun gear) therefore couldn’t apply any torque to the planet carrier, but their rotation would cause the rear unit annulus, both one-way clutches, and the front unit sun gear to all turn backward together. With the front unit annulus locked, the front planetary gearset would multiply this reverse torque and apply it to the planet carrier. Since the second turbine was connected to the front unit annulus, engaging the reverse clutch to lock the annulus also locked the turbine. This essentially transformed the second turbine into a stator, although its purpose was exactly the opposite of Variable Pitch Dynaflow’s forward stator, maximizing rather than removing the negative torque on the third turbine so that torque would be added to the reverse torque the front unit exerted on the output shaft.

The last major element of the triple-turbine transmission was the hill retarder or grade retarder clutch. As we previously mentioned, Twin-Turbine Dynaflow provided little engine braking in Drive and the triple-turbine automatics suffered the same problem. To compensate, both triple-turbine transmissions could be shifted to HR/GR, which engaged the hill clutch — locking the rear annulus — while releasing both the forward clutch and the neutral clutch to disconnect the one-way clutches from the case and the third turbine from the planet carriers. In that condition, only the first turbine could transmit any torque to the output shaft and the rear planetary unit would remain in reduction until the driver shifted to a different range.

In principle, this mode could be used as a low range, although in practice, doing so created too much slippage to have any performance advantage. The real purpose was to provide engine braking: The hill clutch would not unlock even on the overrun, so coasting would cause the rear planetary unit to act as an overdrive, causing the first turbine to attempt to overdrive the engine. This created a strong braking effect, but the rear unit gear ratios were so short — comparable to first gear in many contemporary manual transmissions — that using it at higher speeds was dangerous. (Causing the first turbine to abruptly turn more than twice as fast as the impeller would certainly slow the car, but could overheat the transmission.)

As with most of GM’s early automatics, the triple-turbine triple turbines had front and rear oil pumps, the latter used for push-starting and cruising. These transmissions also adopted Dynaflow’s hydraulic accumulators and Powerglide’s vacuum modulator, adjusting operating and engagement pressures based on load and selector position. The layout of the hydraulic control system, which in complexity now fell somewhere in between Dynaflow and Powerglide, required a new shift pattern: PRNDHR (or PRNDGR) rather than the GM’s previously obligatory PNDLR pattern.

Another unusual and somewhat radical move, at least for the late fifties, was the use of die cast aluminum for the transmission case and the tail housing; cast iron was used only for the hydraulic valve body. This was more expensive and posed some significant manufacturing challenges, but it saved quite a bit of weight. In fact, Chevrolet claimed that Turboglide weighed a substantial 88 lb (40 kg) less than Powerglide, which at that point still had an iron case.

TRIPLE-TURBINE MISFIRE

The point of all this complexity is easy enough to see. Both triple-turbine automatics were what we would now call continuously variable transmissions, offering a highly respectable amount of torque multiplication over a broader range of speeds than any previous automotive torque converter. With its stator blades at their low angle, Turboglide provided a stall ratio of 3.8:1 at a nominal 1,700 rpm, better than the dual-turbine Variable Pitch Dynaflow could manage at full throttle. With the throttle floored to shift the stator blades to high angle, Turboglide’s stall ratio rose to 4.3:1 at a nominal 2,700 rpm, better than Powerglide could offer even in Low. Since Flight Pitch Dynaflow’s stator blades were infinitely variable, Buick quoted only a single ratio: 4.5:1 at a nominal 3,200 rpm in 1958, rising to 4.7:1 for the 1959 Triple Turbine, which had revised impeller and second turbine blades.

On paper, at least, it appeared that GM had finally created the ideal automatic transmission: lightweight and perfectly smooth, with ample torque multiplication. Being (marginally) less complex than some rivals, it also promised to be more reliable. Unfortunately, the reality fell short of the sales pitch.

It should be said that at least part of the problem was one of perception. The triple-turbine transmissions’ torque multiplication depended on keeping the turbine speeds (and thus the speed of output shaft) well behind the speed of the impeller for as long as possible. While that was also true of Twin-Turbine/Variable Pitch Dynaflow, the triple-turbine units’ shorter gearing made the gap between engine speed and output shaft speed more pronounced and thus more noticeable. With an aggressive launch, the speed of the third turbine and output shaft might not approach the speed of the engine until the car was moving more than 50 mph (80 km/h), which could leave the uninitiated driver fearing that the transmission was about to self-destruct. Since the lag in rotational speeds did not directly reflect the transmission’s mechanical efficiency, the slippage wasn’t as nearly dire as it seemed, but it was disconcerting, if nothing else.

As with the dual-turbine Dynaflow, the nonlinearity posed a bigger problem when it came to passing response. Unless output shaft speed fell below about 60% of engine speed, the stator was the sole source of torque multiplication for passing. That was often marginal unless the stator blades were at their highest angle, which even with Buick’s infinitely variable stator was only obtainable with the accelerator floored. Compared to the convenience of Hydra-Matic’s part-throttle kickdowns, this was frustrating, making it seem that the transmission had to be constantly thrashed to provide adequate performance. Naturally, this style of driving did nothing good for overall fuel consumption, although steady-speed economy wasn’t terrible for this era. (Buick nonetheless hedged its bets for 1959 by numerically lowering the standard axle ratio for Triple Turbine cars to 2.78, compared to 3.07 for Twin Turbine or manual shift, which improved fuel economy at further cost in performance.)

Exacerbating this exasperation was the fact the triple-turbine transmissions had no Low range. If the 1.82:1 ratio of Dynaflow’s Low gear was less than ideal, it nonetheless provided immediate relief for any shortage of midrange punch and, with typical late fifties axle ratios, it could be used up to about 60 mph (97 km/h). Turboglide and Flight Pitch/Triple Turbine had only the hill retarder/grade retarder, which was similar to Dynaflow and Powerglide’s Low range only in its position on the selector and was intended for slowing down, not for accelerating. Anyone who shifted from Drive to GR thinking it would improve passing or hill-climbing power was quickly disabused of that notion. (The owner’s manual cautioned against engaging the hill clutch at more than 40 mph (64 km/h), lest you overheat the torque converter.)

As for reliability, it was initially quite poor for both Turboglide and Flight Pitch Dynaflow. One problem was the aluminum case; although aluminum transmission cases would become very common just a few years later, aluminum die castings of this size and complexity were still at the bleeding edge of GM’s metallurgical capabilities (a problem that also dogged the early Buick/Oldsmobile aluminum V8s). On early units, it was not uncommon for the case to crack or split, particularly if the transmission was overheated. It also appears that Chevrolet, at least, underestimated the demands on the clutches — particularly in the area of heat dissipation, which was the primary rationale for the subsequent switch from cone to multi-disc clutches. Even then, the clutches had to be beefed up several times and their engagement pressures increased (among various other changes). Many of the early issues had been addressed by 1959, but neither transmission ever lived down its checkered reputation.

Even if the triple-turbine automatics had been 100% reliable, we suspect that many buyers would have had difficulty seeing the point. That a great many American new car buyers of the time preferred automatic transmission is beyond question, but the need for multiple automatic transmission options was a good deal less obvious. Both Powerglide and Variable Pitch Dynaflow/Twin Turbine certainly had their flaws, but by the late fifties they were well-proven and worked well enough for many customers. The operating principles of Turboglide and Flight Pitch/Triple Turbine are complex enough to mystify even many automotive writers, so it’s easy to imagine the befuddlement of contemporary buyers trying to decide whether the triple-turbine transmissions were worth the attendant price premium. Turboglide’s continuously variable smoothness was a relative novelty for Chevrolet, but for Buick buyers, the dual-turbine Dynaflow, which was also functionally a CVT, was just as smooth. Therefore, the pricier transmission’s notional advantages were probably lost on all but the most technically savvy shoppers.

The upshot of all this was that most buyers shied away, which made both triple-turbine automatics costly failures. Since they shared very little with other Chevrolet and Buick transmissions (although Chevrolet later borrowed some Turboglide pieces for Powerglide), the tooling bill was immense — Buick alone spent a reported $86 million (around $730 million in 2016 dollars) — and warranty costs were high. The extensive changes necessary to address the various reliability problems can’t have helped; we don’t suppose that repeatedly redesigning Turboglide’s clutches was cheap.

Chevrolet, at least, was better able to absorb that expense. For Buick, the failure of Flight Pitch Dynaflow/Triple Turbine was yet another in a long list of calamities to befall the division during this period, doing serious damage to both sales and market share. The new transmission was certainly not the primary culprit — bigger issues included a newly recessionary economy, unpopular styling, and an assortment of assembly woes — but it added yet more red ink to the ledger at a time when Buick could least afford it.

The triple-turbine transmissions also marked an inauspicious period in the career of O.K. Kelley, who had left the Engineering Staff to become Buick’s chief engineer in August 1957. Less than two years later, Buick’s financial woes led to a major shakeup of the division’s upper management, beginning with the replacement of general manager Ed Ragsdale with Edward D. Rollert that April. Kelley departed about seven months later to a new post as chief technical adviser for GM’s Defense Systems Division. Even before he left, Buick terminated production of the Triple Turbine transmission, which vanished at the end of the 1959 model year.

Chevrolet continued to offer Turboglide through the 1961 model year, perhaps in the vain hope of getting their money’s worth. Experience with Turboglide did help Chevrolet engineers develop the Corvair Powerglide and the successful aluminum-case Powerglide (introduced in 1962–63), so it wasn’t a total loss, but all in all, it was not a particularly successful experiment. Looking back on it now, it seems like an intriguing idea that was under-developed and over-sold.

GM’s experience with the triple-turbine automatics was unhappy enough that these transmissions had no direct successors as such. (Kelley also designed a quadruple-turbine transmission, but nothing came of it.) However, some of their design elements did find their way into subsequent GM automatic transmission designs, as we’ll see in the next section.

SENIOR COMPACTS

As we mentioned previously, the late fifties were not a particularly good time for radical or elaborate new designs. The new car market, which had boomed in 1955, slumped badly for 1956. By 1957, a national recession had buyers searching for smaller, cheaper, more economical cars.

Chevrolet general manager Ed Cole used this opportunity to push through his radical rear-engine, air-cooled Corvair, but did nothing to help GM’s mid-priced divisions, which had been hit hard by the recession. Senior corporate management responded with the X-100 project, a collaborative program to give Pontiac, Oldsmobile, and Buick their own small (or at least smaller) cars for the 1961 model year, a year after the debut of the Corvair.

Although the X-100 cars were intended to have a high degree of commonality so as to share the substantial costs of the new models, the final products ended up considerably less alike than the corporation originally hoped. The so-called “senior compacts” — the Buick Special/Skylark, Oldsmobile F-85/Cutlass, and Pontiac Tempest/Le Mans — did share the same unitized Y-body shell (an enlarged version of the Corvair body) and various minor components, but there were significant differences in their mechanical layouts and powertrains, including three completely different automatic transmissions.

Ironically, the most conceptually exotic of the trio, the Pontiac Tempest’s rear-mounted automatic transaxle, was probably the cheapest of the three to develop and tool. Dubbed “TempesTorque,” it was a variation of the Corvair’s optional Powerglide transaxle. As in the Corvair Powerglide, TempesTorque’s torque converter was at the back of the transaxle. Since the Tempest had a front-mounted engine, TempesTorque used the Corvair transmission’s front oil pump driveshaft as an input shaft, driving the torque converter impeller through the torus cover. That input shaft was also splined to the hub of the direct drive clutch, just like in a conventional RWD Powerglide. In high, input torque was therefore split approximately 45/55 between the front sun gear, which was driven by input shaft through the direct drive clutch, and the rear sun gear, which was driven by the torque converter. As with Hydra-Matic, this “split torque” layout served to reduce slippage at cruising speed in high gear.

The 1961–1962 TempesTorque had a lower converter stall ratio than did the Corvair Powerglide (2.00:1 rather than 2.60:1), but the indirect ratios were the same (+/-1.82:1 for low and reverse). As with the Corvair transmission, there was no parking pawl.

Pontiac made a variety of changes to TempesTorque for 1963, the “rope-drive” cars’ final year. Torque capacity was increased to accommodate the Tempest’s newly optional 326 cu. in. (5,340 cc) V8 engine while new planetary gears, borrowed from the latest heavy-duty Powerglide, gave indirect ratios of +/-1.765:1. A new direct drive clutch deleted the previous high-gear torque-splitting feature and the torque converter was redesigned to provide higher stall ratios (2.40:1 for four-cylinder cars, 2.20:1 for the V-8). TempesTorque and the rope-drive Tempest/Le Mans disappeared for good after the 1963 model year.

DUAL-PATH TURBINE DRIVE

The two-speed torque converter automatic transmission offered on Buick’s Y-body compacts, dubbed Dual-Path Turbine Drive, was quite different from TempesTorque and for that matter the twin-turbine transmission used in contemporary full-size Buicks. Today, the Dual-Path Turbine Drive is one of the most obscure and poorly understood of GM’s early automatics, in part because it was used only on the 1961–1963 Buick Special and Skylark. In a sense, it was Buick’s first true automatic transmission, since it was the first to actually include provision for automatic shifts between two distinct stepped ratios in Drive, something the designers had taken pains to avoid with the Dynaflow family.

The Dual-Path transmission seems to represent a merger of two distinct conceptual threads within GM’s corporate transmission group. One was the use of a split-torque clutch to provide direct drive, a concept dating back to the original Hydra-Matic (and which was essayed in somewhat simpler form around 1957 by Oliver Kelley’s colleagues Robert M. Tuck and James J. Mooney, Jr. — see U.S. Patent No. 2,929,270). The other, developed by Kelley and Gilbert K. Hause, was a three-element torque converter with a stator that could do double duty as a drive turbine. Judging by the earliest relevant patent disclosures (U.S. Patents 2,957,370 and 3,030,823), the latter was conceived as a streamlined and simplified evolution of the Twin-Turbine Dynaflow, applying some concepts from the triple-turbine transmissions to allow the deletion of Dynaflow’s separate planetary gearbox.

It appears that there was some consideration of using the Dual-Path transmission in the other X-100 cars. The patent outlining most of the major mechanical details was actually filed by John DeLorean, then the head of Pontiac’s advanced engineering section, although Hause led the development of (and patented) the hydraulic control system. Interestingly, a subsequent patent filed by Kelley and Hause described several possible rear transaxle versions, although the production Dual-Path transmission was only for front-engine/rear-drive applications. The only significant element TempesTorque ended up sharing was the torque-splitting feature, which Pontiac implemented differently.

Like the contemporary Powerglide, Dual-Path Turbine Drive had a three-element torque converter and a single planetary gearset with dual sun gears, but the mechanical similarities ended there. As in the dual-turbine Dynaflow series, the actual planetary gears were nestled in the center of the torque converter torus, with the turbine hub driving the annulus and the planet carrier driving the transmission main shaft. Unlike previous Dynaflow transmissions (and most other automatic transmissions), the impeller was mounted on the flywheel side of the torus housing, facing backward (i.e., toward the rear axle) while the turbine faced forward, toward the engine, and was connected to its hub by a series of narrow struts.

Unlike Powerglide and Dynaflow, Dual-Path Turbine Drive used no brake bands. Instead, it was controlled by four multi-disc clutches (the direct drive/converter clutch, reverse clutch, forward clutch, and coast clutch) and two one-way clutches (one for the stator, the other for the planetary gearset’s rear sun gear). The converter clutch was mounted in the hub of the torque converter impeller, allowing the torus cover to be locked to the planetary gearset’s front sun gear. The other five clutches occupied most of Dual-Path’s cast aluminum transmission case.

The main shaft was surrounded by four concentric sleeve shafts of varying lengths. The outermost sleeve allowed the torus cover to drive the transmission’s single oil pump, which was mounted in the front of the transmission case, like Dynaflow’s front pump. Within that shaft was a sleeve shaft connecting the converter turbine to the hub of the reverse clutch. The two innermost shafts connected the stator and rear sun gear to the inner races of their respective one-way clutches. Those clutches, which were of the cam-and-roller type, shared a common cam, which was connected to the forward clutch and coast clutch. The forward clutch, like the neutral clutch of the Controlled Coupling Hydra-Matic or Triple Turbine transmissions, allowed both one-way clutches to be selectively neutralized (i.e., allowed to turn freely without locking) by disconnecting the cam from the transmission case. The coast clutch, meanwhile, allowed the cam to be locked to the inner race of the rear sun gear so that all three would turn together on the sun gear sleeve shaft.

All this sounds very complex, but Dual-Path’s operation was reasonably straightforward. Selecting either D (Drive) or L (Low) on the selector (which had a PNDLR pattern) would engage the forward clutch. This enabled the one-way clutches for the stator and the rear sun gear, preventing them from turning backward. The hub of the torque converter turbine then drove the annulus of the planetary gearset, with the stator providing additional torque multiplication in the customary fashion; stall ratio was 2.50:1. Reverse torque on the planet carrier locked the rear sun gear’s one-way clutch, putting the planetary gearset in first gear and providing a mechanical gear reduction of 1.58:1.

Selecting L would engage the coast clutch as well as the forward clutch. This allowed the stator to function normally, but prevented the rear sun gear from turning in either direction, ensuring that the planetary gearset would remain in reduction on the overrun. Dual-Path’s hydraulic controls included no provision for automatically disengaging the coast clutch, so in Low, the transmission could not shift out of first gear.

With the selector in D, however, the hydraulic control system would shift automatically between first and second. Upshifts were executed by engaging the converter clutch, which established a mechanical connection between the torus cover and the front sun gear. That drove both sun gears forward, which caused the rear sun gear’s one-way clutch to automatically unlock so that the planetary gearset was no longer in reduction. Engine torque was then split 36.6/63.4 between the front sun gear (which turned at impeller/engine speed) and the annulus (which turned at turbine speed), reducing converter slippage. Downshifts were executed by simply releasing the converter clutch, which caused the rear sun gear to automatically re-lock and put the transmission back in first. Shift points were determined by a combination of throttle setting and car speed. Dual-Path was the first Buick automatic to be equipped with a centrifugal governor, previous Dynaflow and Turbine Drive control units having had no need to measure road speed.

Dual-Path obtained reverse in much the same way as the earlier triple-turbine automatics, although the arrangement was slightly simpler because Dual-Path had only one turbine and one planetary gearset. Moving the selector to R released the forward clutch and engaged both the reverse and coast clutches. The reverse clutch then held the turbine stationary, which caused the turbine and stator to effectively swap roles. With the forward clutch disengaged, releasing the one-way clutch race from the case, reaction torque on the stator caused the stator, its sleeve shaft, and the clutch race to spin backward. Since the coast clutch was also engaged, the reverse rotation of the clutch cam drove the rear sun gear backward. The annulus, which was held in place along with the turbine, then acted as a reaction member, allowing the sun gear to drive the planet carrier in reverse reduction. Mechanical gear ratio in reverse was 2.73:1; the reaction torque created by the stationary turbine would provide additional torque multiplication of 1.50:1, giving a maximum stall ratio in reverse of 4.10:1.

The point of this unusual arrangement was to minimize the number of components, keeping the transmission as compact and as light as possible. With its air-cooled aluminum case, Dual-Path Turbine Drive was one of the lightest automatic transmissions ever developed by a U.S. automaker, weighing only 95 lb (43 kg) with fluid. That was 10 lb (4.5 kg) less than the Buick Special’s standard three-speed Warner Gear T-85 manual transmission and less than half as much as the full-size Turbine Drive or four-speed Hydra-Matic. The transmission tunnel intruded into cabin space only slightly more than that of the rope-drive Tempest, with its rear transaxle.

From a performance standpoint, a two-speed automatic linked to an assortment of modestly powered V8 and V6 engines doesn’t sound promising, but contemporary testers found that cars equipped with Dual-Path were unexpectedly spry. Although Dual-Path’s first gear was quite tall — it was only slightly shorter than second gear in the T-85 three-speed manual or, for that matter, third gear in the Controlled Coupling Hydra-Matic — the torque converter provided a starting ratio comparable to first gear in the four-speed Hydra-Matic. With a 3.08:1 axle, standard on automatic Specials, first could be held to 63–64 mph (101–103 km/h), so Low was useful in mountain driving that would be uncomfortably buzzy with many contemporary two-speeds. In all, performance was really not bad, if still somewhat inferior to the available manual transmissions. The closeness of the ratios and the use of one-way clutches rather than brake bands also made Dual-Path’s shifts impressively smooth.

One minor sacrifice was the capacity for push-starting, something allowed by most earlier GM earlier automatics. Hause’s patent (U.S. No. 3,108,493) included an auxiliary oil pump to be used solely for that purpose, mounted at the rear of the transmission just ahead of the governor. However, the production transmission had only one pump, presumably in the interests of minimizing cost and weight.

ROTO HYDRA-MATIC

Since Oldsmobile’s Y-body compact, the F-85/Cutlass, shared the same basic V8 engine block as the Special (albeit with different cylinder heads and air cleaner), the same three-speed manual transmission, and even the same driveshaft, it would have made sense for the two cars to also share the same automatic transmission. Instead, Oldsmobile opted for a scaled-down version of Detroit Transmission Division’s latest, third-generation Hydra-Matic.

For the sake of clarity, we’ll describe the third-generation Hydra-Matic as “Roto Hydra-Matic,” which is what Pontiac called the transmission in 1963 and 1964; most users simply called it “Hydra-Matic.” (Confusingly, Oldsmobile used the trademark “Roto-Matic” for power steering!) There were actually two different versions of the new transmission: The standard Model 375 (aka Type 61-10) unit was used in full-size Oldsmobiles and some full-size Pontiacs. The light-duty Model 240 (aka Type 61-5) was optional on the Y-body Oldsmobile F-85/Cutlass and on GM’s senior Australian, German, and English cars: the EK (and later EJ) Holden Special, the Opel Kapitän L, and Vauxhall Cresta. The Model 375 was 29 lb (13 kg) heavier than the smaller version, had greater torque capacity, and used fractionally taller (lower numerical) indirect ratios.

Judging by the relevant patent disclosures (U.S. Patents 3,141,354 and 3,132,535), Roto Hydra-Matic was developed by some of the same engineers responsible for the four-speed Controlled Coupling Hydra-Matic, including Walter B. Herndon (with Howard E. Olsen) and August Borman, Jr. (with Charles W. Cline and Carl E. Shellman). The production transmission is typically credited to Detroit Transmission’s assistant chief engineer, Jack W. Qualman, and his boss, Jack R. Doidge. In any case, the new transmission’s conceptual relationship to earlier Hydra-Matics remained evident, although it borrowed a few concepts from the triple-turbine transmissions as well.

Compared to its immediate predecessor, Roto Hydra-Matic was lighter, more compact, and mechanically simpler. There were now only three forward speeds rather than four; two planetary gearsets rather than the previous three; and a single three-element torque converter rather than two fluid couplings. The front overrun clutch and sprag brake were deleted, as was the rear oil pump. The previous neutral clutch was retained, as were the rear overrun band and the reverse cone clutch, although the latter was now part of the front gearset. There was also a new multi-disc front clutch, located between the front unit annulus and the torus cover.

Roto Hydra-Matic’s two planetary gearsets were interconnected by three concentric shafts. The main shaft, innermost of the three, connected the torque converter turbine to the rear gearset sun gear through a vibration damper, a steel-jacketed, splined rubber cushion designed to damp torsional vibrations and keep the main shaft splines from rattling. Around the main shaft was the carrier shaft, which connected the planet carriers of both gearsets to the torque converter’s reaction member and the transmission output shaft. Surrounding the main shaft was a hollow sleeve shaft that linked the reaction members of the two gearsets — the front sun gear and rear annulus — to a single centrally mounted sprag clutch that would hold both elements stationary in first and second gears. The overrun band, which surrounded the the rear annulus, could be engaged to do the same thing. (On the light-duty 61-5 model, both the sprag clutch and overrun band were replaced by a double-wrap brake band, which was engaged in first and second gear and released in third; eliminating the sprag clutch also allowed the deletion of the neutral clutch, since the brake band was completely released in reverse and neutral.)

Interconnecting the two gearsets in this manner meant that their ratios couldn’t be compounded as in earlier Hydra-Matics, which is why Roto Hydra-Matic had only two indirect ratios rather than three. (In fact, the interconnection of the planet carriers meant that putting one gearset in reduction effectively put the other in overdrive, although the overdriven member simply spun idly.) Power flowed through the rear gearset in first and the front gearset in second.

Even more unusual was the torque converter. Derived from the Controlled Coupling Hydra-Matic’s smaller second coupling, it was similar in size — diameter was only 8 inches (203 mm) — and retained the earlier coupling’s dump-and-fill capacity and straight impeller and turbine blades. Nestled within a cutout section of those blades around the converter hub was the converter’s third element: a 22-vane torque multiplier that Oldsmobile marketing pithily dubbed the “Accel-A-Rotor.” The Accel-A-Rotor was not a stator in the customary sense; since it was splined to the carrier shaft, it always rotated at the same speed as the driveshaft and could turn in either direction.

To avoid impairing converter efficiency at cruising speeds, the torque multiplier provided a nominal stall ratio of only 1.30:1. In practice, torque multiplication was both more and less than that modest figure. As explained on page 2, during torque multiplication, oil leaving the turbine exerts reaction torque on the stator. Unlike a conventional stator, Roto Hydra-Matic’s torque multiplier applied that reaction torque directly to the carrier shaft and would actually turn backward if the car was moving in reverse. In principle, that allowed the torque multiplier to function as an auxiliary turbine, although the practical effect was just a small amount of extra leverage in reverse that increased the effective stall ratio to 1.42:1 in that gear. In first, however, the reaction torque on the Accel-A-Rotor resisted the carrier shaft’s forward rotation, reducing the converter’s effective stall ratio to a meager 1.20:1.

Unlike earlier Hydra-Matics, the impeller of Roto Hydra-Matic’s torque converter was driven by the torus cover in more or less conventional fashion and therefore always rotated at engine speed. The converter housing was always full in Park, neutral, first gear, and reverse, enabling the engine to idle without stalling and providing extra torque multiplication when starting. When idling in any forward drive range, the neutral clutch was engaged and the front clutch was disengaged, so Roto Hydra-Matic would always start in first. On the Model 10, moving the selector to Low or S/D-Right, the overrun band would also engage to keep the reaction members locked when coasting; the band wasn’t used at all in normal D/D-Left range. (The Model 5, which didn’t have a sprag clutch, simply left the brake band engaged in those ranges.)

For the 1–2 shift, the torque converter’s oil supply was rapidly emptied; all three elements continued to rotate, but with no working fluid to move, they had no effect. As the converter drained, the front clutch engaged, allowing the torus cover to simultaneously drive the impeller and the annulus of the front gearset. (With the selector in Low, the transmission could not shift into second.) In a panic stop, cut-off valves in the hydraulic control system would quickly refill the converter and disengage the front clutch so the engine wouldn’t stall when the car came to a halt.

For the 2–3 shift, the torque converter was refilled, reestablishing the hydraulic connection between the turbine and the rear sun gear, but this time the front clutch remained engaged. That unlocked the sprag clutch and allowed both gearsets to turn together in direct drive (or near enough). (In S/D-Right range, the shift to third would also automatically release the overrun band; on the lighter 61-5 transmission, which had no sprag clutch, the brake band released on the shift to third.) In third, torque was split three ways: through the front clutch to the front annulus; through the converter turbine to the rear sun gear; and through the torque multiplier to the carrier shaft.

Discounting the unusual behavior of the torque multiplier, reverse functioned much the same way as in earlier Hydra-Matics. Moving the selector to Reverse disengaged both the front clutch and the neutral clutch (or brake band) while engaging the reverse cone clutch to lock the front annulus. The torque converter drove the rear sun gear, just as in first, but with the neutral clutch now released to neutralize the sprag clutch (or, on light-duty models, with the brake band released), the rear sun gear drove the rear annulus — and with it the front sun gear — backward. The stationary front annulus served as a reaction member, causing the driven planet carrier — and thus the carrier shaft and driveshaft — to rotate backward in reduction.

The following table summarizes the shift sequence for the full-size Roto Hydra-Matic. (Again, “REL” = “RELEASED” and “ENG” = “ENGAGED”; you can probably guess that “Torque Conv.” = “Torque Converter.”)

Like its predecessors, Roto Hydra-Matic placed Reverse at the far end of the shift pattern, adjacent to Low, and allowed the car to be “rocked” by moving the selector back and forth between Low and Reverse. A reverse blocker (theoretically) prevented the transmission from going into reverse if the car was moving faster than a crawl. However, as with Dual-Path Turbine Drive, there was no longer any provision for push-starting. The single oil pump was now driven directly off the engine flywheel, so neither could be driven by the propeller shaft with the engine off.

Roto Hydra-Matic was even smoother than the four-speed Controlled Coupling Hydra-Matic, but a certain amount of performance was sacrificed in the process. In fact, many contemporary reviewers judged the three-speed Hydra-Matic in the Oldsmobile F-85 inferior to the two-speed Dual-Path Turbine Drive used in the Buick Special or even Powerglide in both performance and shift quality. Part of the problem was that Roto Hydra-Matic’s shifts were now quite slow. The adoption for 1962 of a new hydraulic pressure control system allowed shift speed and firmness to vary with engine torque, which helped some, but the assertive shift quality that was once a Hydra-Matic hallmark was now long gone.

A bigger issue, so far as performance was concerned, was that the three-speed transmission’s ratios (listed in the table below) were far from ideal. Despite the torque multiplier and a rather short first gear, starting ratios were still taller than the four-speed unit’s. That wouldn’t have been so bad, but Roto Hydra-Matic’s second and third gears were closer to third and fourth in the dual-coupling Hydra-Matic, leaving a big gap between first and second that the torque multiplier (which was ineffective once the car was in motion) could not plug. The annoyance of the ratio gap was compounded by the hydraulic control system’s frustrating tendency to vacillate between second and third.

Another unhappy peculiarity was a penchant for oil leaks. We don’t know all the factors that may have contributed to that problem, although we wonder if it was partly related to Roto Hydra-Matic’s operating pressures, which were generally higher than with its four-speed predecessor and may have tested the integrity of the seals. Particularly noteworthy is the fact that converter charging pressure was quadrupled (to 180 psi/12.41 bars) to make up for the torque capacity sacrificed to the torque converter’s diminutive size. We assume the rationale for the small diameter was, as before, to facilitate rapid drainage and refilling. The dilemma, of course, was that the dump-and-fill coupling in the earlier Controlled Coupling Hydra-Matic never had to bear more than 40% of input torque; Roto Hydra-Matic’s torque converter had to bear the full engine output in first gear.

The good news was that the new layout, along with a switch from cast iron to aluminum for the transmission case, made Roto Hydra-Matic — soon nicknamed “Slim Jim” — more compact and some 75 to 95 lb (34 to 43 kg) lighter than the dual-coupling Hydra-Matic (which remained in production for Cadillac and some Pontiacs). It was also cheaper to build, if not to buy.

(To the latter point, we should note that while the list prices of automatic transmissions had crept steadily upward since the forties, that inflation had been at a somewhat slower rate than the inflation in new car prices. Thus, while automatic transmissions weren’t getting any cheaper, the price of the option as a percentage of the cost of a new car had actually decreased.)

THE END OF THE LINE

By the mid-sixties, the autonomy GM had long allowed its individual automotive divisions was beginning to give way to a new emphasis on inter-divisional commonality. We don’t know if the Y-body compacts represented some kind of breaking point in that regard, but we wouldn’t be surprised. Their development and manufacturing costs had been high — higher, we have little doubt, than most of GM’s contemporary full-size cars, and largely concentrated in areas that the average buyer wouldn’t even notice — and sales had been disappointing, which was a recipe for lackluster profits.

During this period, GM began a belated move toward standardized transmissions. Having multiple automatic transmissions probably seemed reasonable when Buick was selling more cars than Plymouth and half the industry used Hydra-Matic, but the market downturn and various missteps of the late fifties and early sixties made the proliferation of sui generis transmissions seem like economic folly. The three-year production total for Dual-Path Turbine Drive, for example, was well short of the average annual volume of the early-fifties Hydra-Matic. Numbers like that made it harder to justify the R&D and tooling costs of multiple transmission designs.

GM initially opted for a two-pronged approach: a new two-speed automatic for Buick, Oldsmobile, and Pontiac A-body intermediates, which replaced the Y-body compacts for 1964, and a new three-speed transmission to replace the Roto Hydra-Matic and Controlled Coupling Hydra-Matic in bigger cars. Chevrolet, whose annual production generally exceeded the combined totals of the other four automotive divisions, continued to build and use its own two-speed Powerglide.

The new transmissions were developed by engineers from the corporate transmission group and Detroit Transmission Division, which was formally renamed Hydra-Matic Division on October 1, 1963. The two-speed, which Buick called Super Turbine 300 (ST-300) and Oldsmobile called Jetaway, was mechanically very similar to the aluminum-case Powerglide, using a Ravigneaux gearset to provide indirect ratios of +/-1.765:1. The three-speed unit was the Turbo Hydra-Matic 400 (TH-400), which Buick called Super Turbine 400 (ST-400), an all-new design using a licensed version of Howard W. Simpson’s patented “Simpson gearset“: two planetary gearsets sharing a single common sun gear. Both transmissions had three-element torque converters and used a new type of vacuum modulation.

Some sources — including contemporary Buick publicity and marketing material — suggest a lineal connection between these transmissions and the earlier Dynaflow/Turbine Drive, Dual-Path, and Hydra-Matic units they replaced, which was really only true in certain broad or incidental ways. Gone for good were the multiple turbines, dump-and-fill couplings, and split torque clutches (although Turbo Hydra-Matic would eventually add a lockup torque converter clutch in the pursuit of better fuel economy). The one exception was that some 1964–1967 ST-300/Jetaway and 1965–1967 ST-400/TH-400 transmissions used a two-position variable-pitch stator, similar in principle to the one Dynaflow had first adopted back in 1955. However, the pitch angles were different and the stator servo control valve was now operated by a solenoid triggered by the kickdown switch. Pontiac and Chevrolet never used the “switch-pitch” stator, nor did Series Seventy-Five Cadillacs; other users deleted the feature after the 1967 model year.

The new two-speed automatic was first offered on the 1964 A-body Buick Special/Skylark, Oldsmobile F-85/Cutlass, and Pontiac Tempest/Le Mans/GTO and the B-body Buick LeSabre and Oldsmobile Jetstar 88. At the same time, Turbo Hydra-Matic replaced Turbine Drive on full-size Buicks (including the Riviera) and superseded the four-speed Hydra-Matic on the Cadillac DeVille, Sixty Special, and Eldorado. All remaining U.S. users of both earlier Hydra-Matics switched to TH400 for the 1965 model year. In mid-1965, Chevrolet also began offering Turbo Hydra-Matic as an option for full-size cars equipped with the new 396 cu. in. (6,488 cc) “Turbo Jet” engine. Turbo Hydra-Matic became available on certain A-body intermediates for 1967 and on the Corvette for 1968.

By the late sixties, two-speed automatics were becoming increasingly anachronistic, so the ST-300/Jetaway was relatively short-lived. Starting in 1969, both ST-300/Jetaway and Powerglide were phased out in favor of scaled-down, medium- and later light-duty versions of Turbo Hydra-Matic. Two-speed automatics had disappeared from all of GM’s North American cars by the 1974 model year.

The mechanics and further development of Turbo Hydra-Matic (sometimes styled “Turbo Hydra-matic” or “Turbo-Hydramatic”) are beyond the scope of this article, but suffice to say it was a very successful and generally well-regarded line. Like the old four-speed Hydra-Matic, the TH400 was also used by a variety of outside automakers, including Rolls-Royce and Bentley, Jaguar, and even Ferrari.

In 1983, GM chairman Roger Smith ordered the consolidation of all the corporation’s transmission plants under the control of Hydra-Matic Division, eliminating the last vestiges of the old divisional rivalry. In the early nineties, GM created GM Powertrain by combining Hydra-Matic Division with GM Engine and later the Central Foundry Division and the Advanced Engineering Staff, the heirs of the group that originally developed Hydra-Matic and Dynaflow.

Since 2010, the GM Powertrain group has been part of the larger Global Products Operations organization, although the Hydra-Matic name is still in use — and of course remains a registered trademark of General Motors. Modern Hydra-Matic transmissions, however, bear only a faint resemblance to their pioneering and sometimes peculiar forebears.

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AUTHOR’S NOTE

The author would like to offer special thanks to reader Dave Ostroska for generously providing us with a copy of the factory service manual for the Buick Dual-Path Turbine Drive, which is now quite hard to find.

NOTES ON SOURCES

Information on the development of Dynaflow, Powerglide, and Dual-Path Turbine Drive and their antecedents (including Buick’s earlier IV “Roller” friction drive) came from William C. Anderson, “Charles A. Chayne, Buick’s Unsung Hero,” The Buick Bugle September 2003, www.buickheritagealliance. org/ pdf/ chayne.pdf, accessed 20 May 2010; Ray T. Bohacz, “Mechanical Marvels: Smooth Operator: Buick’s Dynaflow Automatic Transmission,” Hemmings Classic Car #77 (February 2011), pp. 70–72; Griff Borgeson, “Buick Has Looks, Plus Ride at Moderate Price,” Motor Trend Vol. 3, No. 10 (October 1951), reprinted in Buick Performance Portfolio 1947-1962, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 2000), pp. 25-27, and “Road Test: Buick’s New Century,” Motor Life April 1954, reprinted in ibid, pp. 44–47; Arch Brown, “High-Fashion Hauler: 1948 Buick Roadmaster Estate Wagon,” Special Interest Autos #136 (July-August 1993): pp. 12–19, 62–63; “Out Front Again! 1950 Chevrolet Bel Air,” Special Interest Autos #108 (November-December 1988), reprinted in The Hemmings Book of Postwar Chevrolets: driveReports from Special Interest Autos magazine, eds. Terry Ehrich and Richard Lentinello (Bennington, VT: Hemmings Motor News, 2001), pp. 4-10; “SIA comparisonReport: 1954 vs. 1955 Chevrolet,” Special Interest Autos #100 (July-August 1987), reprinted in ibid, pp. 36–44; “SIA comparisonReport: Upper Middle Class ‘Class’: 1948 Buick Roadmaster, 1948 Chrysler New Yorker,” Special Interest Autos #167 (September-October 1998), reprinted in The Hemmings Book of Buicks: driveReports from Hemmings Special Interest Autos magazine, eds. Terry Ehrich and Richard Lentinello (Bennington, VT: Hemmings Motor News, 2001), pp. 24–33; Buick Motor Division of General Motors Corporation, “Buick’s Greater Cars in 50 Great Years” [brochure 500M], January 1953; “Buick ’60: Portfolio of Fine Cars” [brochure, ca. Oct. 1959]; “Buick takes the bows for ’48” [brochure], April 1948; “For 1957: Newest Buick Yet” [brochure, ca. October 1956]; “Front and Center for 1952 — Buick” [brochure, ca. 1952]; “Full Size 1961 Buick” [brochure, ca. 1961]; “1955 Buick: Forefront of fashion—Thrill of the year” [brochure], 1955; 1955 Buick Shop Manual (Flint, Michigan: 1955); “1956 Buick carries the banner forward” [brochure], 1956; 1961 Buick Special Service Manual BPS 1.51 (Flint, MI: Buick Division of General Motors Corporation, 1961); 1953 Buick Owner’s Guide, Third Ed. (Flint, MI: Buick Motor Division of General Motors Corporation, 1953); “Special: The Happy Medium-Size Car!!!” [brochure], 1962; “The Air Born [sic] B-58 Buick” [brochure, ca. October 1957]; “The Car: Buick ’59” [brochure, ca. Oct. 1958]; “The New Special Size 1961 Buick Special” [brochure, ca. October 1960]; “The trim-size Buicks for ’63” [Special/Skylark brochure, ca. October 1962]; and Variable Pitch Dynaflow, Second Edition (Flint, MI: Buick Motor Division, General Motors Corporation, 1955); “Buick Stories by Phil,” Buick Street, 2005, www.buickstreet. com/ buickstories.html, accessed 1 December 2015; “Buick Toe the Line,” The Autocar 3 February 1956, reprinted in Buick Performance Portfolio 1947-1962, p. 54; “Car Life Road Test: Buick Invicta,” Car Life Vol. 9, No. 11 (December 1961), reprinted in ibid, pp. 128–131; Charles S. Chapman and Rudolph Gorsky, “The Dual Path Turbine Drive,” The SAE Journal Vol. 69, No. 4 (April 1961), pp. 80–83; Charles A. Chayne, “Buick’s Dynaflow Drive,” The SAE Journal Vol. 56, No. 4 (April 1948), pp. 23–29; Chris Chant, “M18 Hellcat – The USA’s primary tank destroyer of WWII,” 10 July 2013, www.cmchant. com/ m18-hellcat-the-usas- primary-tank-destroyer-of-wwii, accessed 20 September 2015; “Chevrolet Impala Super Sport 409 V-8 with Powerglide,” Car Life Vol. 11, No. 2 (March 1963), reprinted in Impala & SS Muscle Portfolio 1958–1972, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1996), pp. 42–46; Chevrolet Motor Division of General Motors Corporation, “Chevrolet for 1961” [brochure, ca. October 1960]; “New Chevy II” [brochure, ca. October 1961]; Chevrolet 1950–1953 Powerglide Automatic Transmission Repair Manual (Detroit, MI: General Motors Corporation, 1952); Chevrolet 1950 Engineering Features: Passenger Cars (Detroit, MI: General Motors Corporation, 1949); 1953 Engineering Features: Passenger Cars (Detroit: General Motors Corporation, December 1952); “1962 Chevrolet” [brochure, ca. October 1961]; Servicing the Powerglide Transmission: Maintenance, Adjustment, Removal, and Installation (MTS Release No. 50-1), (Detroit, MI: General Motors Corporation, 1950); “’63 Chevrolet” [brochure, ca. October 1962]; “The 1954 Chevrolet” [brochure, ca. October 1953]; and Technical Service Department, Aluminum-Case Powerglide Training Program Booklet (TP-21), April 1962; Chevrolet Engineering Center, Engineering Product Information Department, 1958 Chevrolet Passenger Car Engineering Features (Warren, MI: October 1957), and 1959 Chevrolet Passenger Car Engineering Features (Warren, MI: October 1958); “Chevrolet Nova 396 SS [sic] Coupe,” Road Test July 1970, reprinted in Chevy II · Nova & SS Muscle Portfolio 1962–1974, ed. R.M. 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Dunham and Lawrence R. Gustin, The Buick: A Complete History (An Automobile Quarterly Magnificent Marque Book) (Kurtztown, PA: Automobile Quarterly, 1980); Jim Dunne and Jan P. Norbye, Buick 1946-1978: The Classic Postwar Years, Second Edition (Osceola, WI: MBI, Inc./Motorbooks International, 1993); David Edwards, Antique Automatic Transmission Parts, www.autotran.us; Devon Francis, “New Buick Flows from Low to High,” Popular Science Vol. 152, No. 2 (February 1948), pp. 113–118, and “What You Should Know About Automatic Drives,” Popular Science Vol. 156, No. 4 (April 1950), pp. 99-105; Joseph Geschlin, “Making the Dynaflow—An Exacting Precision Job,” Automotive Industries Vol. 98, No. 9 (May 15, 1948), pp. 26–27, 88–91; the GM Heritage Archive (gmheritagecenter. com/ gm-heritage-archive/); Philip G. Gott, Changing Gears: The Development of the Automotive Transmission (SAE Historical Series) (Warrendale, PA: Society of American Engineers, 1991); Winfield D. Gove and John Dolza, assignors to General Motors, “Torque Loading Lash Adjusting Device for Friction Roller Transmissions,” U.S. Patent No. 2,030,203 A, filed 31 May 1934, issued 11 February 1936; T. Grace, Automatic Transmission Service Guide (Union, NJ: Lincoln Technical Institute, September 1966); John Gunnell, ed., Standard Catalog of American Cars 1946-1975 Revised 4th Edition (Iola, WI: Krause Publications, 2002), and Standard Catalog of Buick 1903-2004 Rev. 4th Ed. (Iola, WI: Krause Publications, 2004); Gilbert K. Hause, assignor to General Motors Corporation, “Transmission,” U.S. Patent No. 3,108,493, filed 6 November 1958, issued 29 October 1963; “Split Torque Transmission,” U.S. Patent No. 3,039,325, filed 29 November 1960, issued 19 June 1962; and “Multiple Speed Split Torque Transmission,” U.S. Patent No. 3,084,569, filed 24 July 1961, issued 9 April 1963; Gilbert K. Hause and Oliver K. Kelley, assignors to General Motors Corporation, “Multi-Phase Transmission,” U.S. Patent No. 3,062,074, filed 19 February 1958, issued 6 November 1962; “How the New Buick Century Performs,” Science and Mechanics June 1954, reprinted in Buick Performance Portfolio 1947-1962, pp. 40–41; Roger Huntington, “The Great Transmission Controversy: Coupling vs. Converter,” Car Life Vol. 10, No. 2 (March 1962), pp. 18-25; “Is Buick’s 50th Year Its Best?” Motor Trend Vol. 5, No. 7 (July 1953), reprinted in Buick Performance Portfolio 1947-1962, pp. 33–36; Oliver K. Kelley, assignor to General Motors Corporation, “Combination Fluid Turbo Clutch and Variable Speed Gearing,” U.S. Patent No. 2,176,138, applied 5 February 1937, issued 17 October 1939; “Fluid Flywheel Gearing Arrangement,” U.S. Patent No. 2,211,233, applied 10 April 1939, issued 13 August 1940; and “Transmission Drive,” U.S. Patent No. 2,377,696, filed 15 December 1941, issued 5 June 1945; “Compound Power Transmission,” U.S. Patent No. 2,433,052, filed 6 September 1943, issued 23 December 1947; “Combined Transmission,” U.S. Patent No. 2,606,460, filed 29 November 1944, issued 12 August 1952; “Tank Cross Drive for Steering by Variable-Speed Ratio Driving Means,” U.S. Patent No. 2,585,790, filed 16 April 1945, issued 12 February 1952; “Fluid Drive and Controls,” U.S. Patent No. 2,625,056, filed 14 September 1946, issued 13 January 1953; “Rotary Hydraulic Torque Converter,” U.S. Patent No. 2,687,616, filed 11 January 1949, issued 31 August 1954; “3-Phase Turbine Drive,” U.S. Patent No. 2,737,061, filed 19 November 1949, issued 6 March 1956; “Fluid Control for Rotary Turbine Type Hydraulic Torque Converters,” U.S. Patent No. 2,638,746, filed 30 November 1949, issued 19 May 1953; “Dual Range Plural Turbine Gear Drive,” U.S. Patent No. 2,766,641, filed 8 November 1950, issued 16 October 1956; “Multiple Rotor Converter Having Plural Impellers,” U.S. Patent No. 2,727,360, filed 23 November 1951, issued 20 December 1951; “Hydrodynamic Torque Converter and Gearing,” U.S. Patent No. 2,782,659, filed 18 June 1952, issued 26 February 1957, reissued 14 March 1961; “Four Phase Converter Drive,” U.S. Patent No. 2,803,974, filed 5 August 1953, issued 27 August 1957; “Four Phase Converter Drive,” U.S. Patent No. 2,981,124, filed 5 August 1953, divided 25 April 1957, issued 25 April 1961; “Hydrodynamic Torque Converters and Controls Therefor,” U.S. Patent No. 2,999,400, filed 13 January 1954, issued 12 September 1961; “Hydrodynamic Torque Converters,” U.S. Patent No. 2,910,832, filed 22 July 1954, issued 3 November 1959; “Transmission,” U.S. Patent No. 2,821,095, filed 19 October 1955, issued 28 January 1958; “Hydraulic Torque Converter,” U.S. Patent No. 2,882,684, filed 17 July 1956, divided 31 July 1957, issued 21 April 1959; “Transmission,” U.S. Patent No. 2,882,751, filed 17 July 1956, divided 31 July 1957, issued 21 April 1959; “Hydrodynamic Torque Converters,” U.S. Patent No. 3,025,720, filed 26 March 1958, issued 20 March 1962; “Transmission,” U.S. Patent No. 3,030,823, filed 11 July 1957, issued 24 April 1962; and “Transmission,” U.S. Patent No. 3,242,677, filed 29 September 1955, issued 29 March 1966; Oliver K. Kelley and Gilbert K. Hause, assignors to General Motors Corporation, “Multi-Phase Torque Converter,” U.S. Patent No. 2,957,370, filed 11 July 1957, issued 25 October 1960; Oliver K. Kelley and John D. Lindsay, assignors to General Motors Corporation, “Multiple Stator Torque Converter,” U.S. Patent No. 3,025,719, filed 28 December 1954, issued 20 March 1962; Oliver K. Kelley and Robert S. Plexico, assignors to General Motors Corporation, “Transmission Control System,” U.S. Patent No. 2,865,227, filed 4 June 1952, issued 23 December 1958; Oliver K. Kelley and Robert M. Schaefer, assignors to General Motors Corporation, “Composite Fluid and Gear Drive,” U.S. Patent No. 2,782,658, filed 18 January 1951, issued 26 February 1957; Oliver K. Kelley and William S. Wolfram, assignors to General Motors Corporation, “Rotary Hydraulic Torque Converter with Dynamic Braking,” U.S. Patent No. 2,651,918, filed 30 July 1949, issued 15 September 1953; Carroll K. Lenning, assignor to General Motors Corporation, “Transmission Drive Cooling System,” U.S. Patent No. 2,270,536, filed 17 February 1940, issued 20 January 1942; Jim Lodge, “’55 Buick Roadmaster Special,” Motor Trend Vol. 7, No. 7 (July 1955), reprinted in Buick Performance Portfolio 1947-1962, pp. 50–53, 71 “’56 Buick Special and Century,” Motor Trend Vol. 8, No. 6 (June 1956), reprinted in ibid, pp. 56-59, and ; Joseph Lowrey, “Dynaflow Drive in the Alps,” The Motor 20 April 1949, reprinted in ibid, pp. 14-18; “M18 Hellcat Tank Destroyer,” n.d, m18hellcat. com/m18hellcat/ Home.html, accessed 20 September 2015; L.H. Nagler, “How Your Car Shifts for Itself,” Popular Mechanics Vol. 89, No. 5 (May 1948), pp. 102–106, 264, 268, 272; Chuck Nerpel, “Buick Invicta,” Motor Trend Vol. 12, No. 6 (June 1960), reprinted in Buick Performance Portfolio 1947-1962, pp. 100–104; “New Dynaflow Buicks,” The Motor 8 December 1948, reprinted in Buick Performance Portfolio 1947-1962, pp. 10–13; Paul Niedermeyer, “Powerglide: A GM’s Greatest Hit or Deadly Sin?” Curbside Classic, 30 March 2012, www.curbsideclassic. com/automotive-histories /powerglide-gms-greatest-hit-or-deadly-sin/, last accessed 4 January 2016; “1951 Chevrolet,” Special Interest Autos #17 (June-July 1973), reprinted in The Hemmings Book of Postwar Chevrolets, pp. 12–17; the Old Car Brochures website (oldcarbrochures.org); the Old Car Manual Project (www.oldcarmanualproject. com); “Packard’s Ultramatic Drive,” Product Engineering July 1949, reprinted in Packard Gold Portfolio 1946-1958, pp. 22–24; Robert S. Plexico and Russell E. Kaufman, “Chevrolet’s Automatic Transmission, The SAE Journal Vol. 58, No. 3 (March 1950), pp. 27–33; Jim Potter, “’54 Buick Special,” Motor Trend Vol. 6, No. 10 (October 1954), reprinted in Buick Performance Portfolio 1947-1962, pp. 42–43; “Road & Track Road Test: Buick Special V-6,” Road & Track Vol. 11, No. 3 (November 1961), reprinted in Buick Performance Portfolio 1947-1962, pp. 124-127; “Road Test: Buick Century,” Motor Life March 1955, reprinted in ibid, pp. 48–49, 63; “Road Test: The Buick V-8,” Motor World 22 May 1953, Buick Performance Portfolio 1947-1962, pp. 37–38; “Road Test: The Invicta and the Special,” Motor Life January 1961, reprinted in ibid, pp. 112-119; “Road Test – The 1956 Buick Century,” Motor Life May 1956, reprinted in ibid, pp. 60–61; Maurice S. Rosenberger, “Transmission Control System,” U.S. Patent No. 2,766,639, filed 8 November 1952, issued 16 October 1956, reissued 5 June 1962; Christian Seabaugh, “1944 Buick M18 Hellcat Tank Destroyer First Drive: Seek, Strike, Destroy!” Truck Trend 28 October 2013, www.trucktrend. com, accessed 20 September 2015; Wilbur Shaw, “Buick Hooks New V-8 to Dynaflow+Gears,” Popular Science Vol. 162, No. 2 (February 1953), pp. 159–162, 248; Don Sherman, “Reviews: Buick Hellcat Tank,” Automobile February 2005, www.automobilemag. com, accessed 20 May 2010; Alfred P. Sloan with John McDonald, My Years with General Motors (Garden City, NY: Doubleday, 1964); Edwin Storm’s Free Car Brochures website at the Old Car Manual Project (storm.oldcarmanualproject. com); Robert Temple, “Transmissions and Drive Lines (Know Your Car Part Two),” Motor Trend Vol. 15, No. 1 (January 1963), pp. 54-59; “The Autocar road tests 1814: Buick Special,” The Autocar 31 March 1961: 494–497; “The New Buicks: Slicker, Smoother,” Popular Science Vol. 153, No. 6 (December 1948), pp. 106–107; “The New Buick: With Hydraulic Torque Converter and Two-speed Epicyclic Gear,” The Motor 21 January 1948, reprinted in Buick Performance Portfolio 1947-1962, pp. 6-9; Wayne Thoms, “Road Trial: Buick Special,” Motor Trend Vol. 12, No. 12 (December 1960), pp. 22–27; Robert M. Tuck and James J. 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Additional information on the Controlled Coupling Hydra-Matic came from August H. Borman, Jr.; Forrest R. Cheek; and Milton H. Scheiter, assignors to General Motors Corporation, “Controlled Coupling Automatic Transmissions,” U.S. Patent No. 3,048,055, filed 27 December 1954, issued 7 August 1962; Ray Brock, “Olds … ’59 Class Leader,” Hot Rod June 1959, reprinted in Oldsmobile Automobiles 1955–1963, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1989), pp. 44–48, 60; “Olds 88 for ’60,” Hot Rod January 1960, reprinted in ibid, pp. 51–55; and “Pontiac – 3000 Mile Road Test,” Hot Rod December 1958, reprinted in Pontiac Limited Edition: 1949-1960, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1999), pp. 74–79, 89; Arch Brown, “1957 Nash Ambassador: Twilight of the Dinosaurs,” Special Interest Autos #115 (January-February 1990), reprinted in The Hemmings Book of Nashes: driveReports from Special Interest Autos magazine, eds. Terry Ehrich and Richard A. Lentinello (Bennington, VT: Hemmings Motor News, 2002), pp. 110–117; “1959 Cadillac Eldorado Biarritz: Nothing Succeeds Like Excess,” Special Interest Autos #88 (August 1985), reprinted in Cadillac Automobiles 1949–1959, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1990), pp. 92–100; the Cadillac & LaSalle Club Modified Chapter website (www.modifiedcadillac.org); Cadillac Motor Car Division of General Motors Corporation, “Cadillac data book ’56,” September 1955; “Car Life Consumer Analysis: 1956 Cadillac,” Car Life Vol. 4, No. 5 (June 1956), reprinted in Cadillac Automobiles 1949-1959, pp. 52–53; “Car Life Consumer Analysis: 1956 Pontiac,” Car Life Vol. 4, No. 2 (March 1956), reprinted in Pontiac Limited Edition: 1949-1960, pp. 46–47; Floyd Clymer, “Owners Praise Cadillac’s Performance But Complain of Transmission Troubles,” Popular Mechanics Vol. 105, No. 4 (April 1956), pp. 105–108, 250–258; “Controlled Coupling Hydra-Matic Fundamentals,” Chilton’s Auto Repair Manual (Philadelphia, PA: Chilton Book Company, 1958), pp. 79-132; Jack R. Doidge and Victor C. Moore, assignors to General Motors Corporation, “Transmission,” U.S. Patent No. 2,947,199, filed 26 November 1957, issued 2 August 1960; Walter B. Herndon, assignor to General Motors Corporation, “Controlled Coupling Multistep Automatic Transmissions,” U.S. Patent No. 2,876,656, filed 23 November 1953, issued 10 March 1959; and “Variable Capacity Pressure System for Transmissions,” U.S. Patent No. 2,875,699, filed 19 July 1954, issued 3 March 1959; Bill Holland, “Bill Holland Tests … The Cadillac 60 Special,” Motorsport May 1956, reprinted in Cadillac Automobiles 1949-1959, pp. 54–56; “Hydra-Matic Dampens That Thump,” Popular Science Vol. 167, No. 5 (November 1955), pp. 119–121, 260; John F. Katz, “1956 Oldsmobile Super 88 Convertible,” Special Interest Autos #145 (January-February 1995), reprinted in The Hemmings Book of Oldsmobiles: driveReports from Hemmings Special Interest Autos magazine, ed. Terry Ehrich (Bennington, VT: Hemmings Motor News, 2001), pp. 65-74; and “1960 Pontiac Bonneville Vista,” Special Interest Autos #172 (July-August 1999), reprinted in The Hemmings Motor News Book of Pontiacs: driveReports from Hemmings Special Interest Autos magazine, ed. Terry Ehrich (Bennington, VT: Hemmings Motor News, 2001), p. 68-77; Oliver K. Kelley, assignor to General Motors Corporation, “Combination Fluid Turbo Clutch and Variable Speed Gearing,” U.S. Patent No. 2,176,138, applied 5 February 1937, issued 17 October 1939; “Fluid Flywheel Gearing Arrangement,” U.S. Patent No. 2,211,233, applied 10 April 1939, issued 13 August 1940; and “Transmission Drive,” U.S. Patent No. 2,377,696, filed 15 December 1941, issued 5 June 1945; Dale Kelly, “An Engineer Analyzes the 1957 Oldsmobile,” Popular Mechanics Vol. 108, No. 1 (July 1957), reprinted in Oldsmobile Automobiles 1955–1963, pp. 25–26; Al Kidd, “drivescription: ’56 Oldsmobile,” Motor Trend Vol. 7, No. 12 (December 1955) and “’56 Oldsmobile Road Test, “Motor Trend Vol. 8, No. 4 (April 1956), reprinted in ibid, pp. 12-13 and 16-19; Ed Mobley, “Controlled Coupling Hydramatic/Jetaway Automatic Rebuild,” Edscars, 2006, www.photopaige. com/ edscars/ 60caddy/ CaddyWebSitev2_files/ TrannyRebuild2.htm, accessed 29 May 2010; Victor C. Moore, assignor to General Motors Corporation, “Transmission,” U.S. Patent No. 2,919,607, filed 30 November 1956, issued 5 January 1960; “New Cars Described: 1956 Pontiacs Have Latest Transmission,” The Autocar 18 November 1955, reprinted in Pontiac Limited Edition: 1949-1960, p. 45; “1960 Pontiac Tempest,” Hot Rod May 1960, reprinted in Pontiac Limited Edition: 1949-1960, pp. 86–89; Oldsmobile Division, General Motors Corporation, “’58 Oldsmobile” [brochure, ca. November 1957]; “Oldsmobile” [1956 brochure, ca. October 1955]; and “Oldsmobile’s New Jetaway Hydra-Matic” [brochure], 1955; Pontiac Motor Division of General Motors Corporation, “Answers That Sell: 1964 New Product Facts” [dealer literature], 30 August 1963; “Facts About the New ’56 Pontiac: Star Chief, 870 and 860 series” [dealer literature], September 1955; “Introducing Your 1957 Pontiac” (Pontiac 1957 Owner’s Guide S-5701), January 1957; 1957 Hydra-Matic Manual (with 1956 Appendix) (Pontiac, MI: Pontiac Motor Division, General Motors Corporation, March 1957); and “Pontiac ’58” [brochure, ca. October 1957]; “Oldsmobile: not the rocket it used to be,” Motor Life March 1960, reprinted in Oldsmobile Automobiles 1955–1963, pp. 56–57; “Oldsmobile Road Test,” Motor Life February 1959, reprinted in ibid, pp. 42–43; “Power Is Oldsmobile’s Top Feature, Say Owners from Coast to Coast,” Popular Mechanics Vol. 108, No. 1 (July 1957), reprinted in ibid, pp. 24–26; “The 1956 Cadillac,” Motor Life December 1955, reprinted in Cadillac Automobiles 1949-1959, p. 49; William K. Toboldt and Larry Johnson, Goodheart-Willcox Automotive Encyclopedia (South Holland, IL: The Goodheart-Willcox Company, Inc., 1975); Johnny Tolan, “Johnny Tolan Tests the ’57 Oldsmobile,” Speed Age March 1957, reprinted in Oldsmobile Automobiles 1955–1963, pp. 20–23; United Motors Service Division, The Hydra-Matic Transmission 1946-1955: On-the-Car Adjustment Service Manual (Detroit, MI: United Motors Service Division of General Motors Corporation, 1956), and Hydra-Matic Controlled Coupling Transmission Service Manual (Bulletin A-3755) (Detroit, MI: United Motors Service Division of General Motors Corporation, 1 November 1957); U.S. War Department, Ordnance Maintenance: Hydra-Matic Transmission and Propeller Shafts for Light Tanks M5, M5A1, and 75-MM Howitzer Carriage (War Department Technical Manual TM 9-1727C (Washington, DC: U.S. Government Printing Office, 5 February 1943); Joe H. Wherry, “’58 Oldsmobile on trial,” Motor Trend Vol. 10, No. 3 (March 1958), reprinted in Oldsmobile Automobiles 1955–1963, pp. 30–35; and Otto Zipper, “Road Test: Two Pontiacs,” Motor Trend Vol. 9, No. 3 (March 1957), reprinted in Pontiac Limited Edition: 1949-1960, pp. 54–57, 59. John D. Kelly later helped us to sort out some technical points about the original single-coupling unit in emails to the author, 7 to 8 March 2017.

Additional information on the triple-turbine automatics came from Al Berger, “’59 Chevrolet Has Fins, Will Travel,” Speed Age December 1958, reprinted in Impala & SS Muscle Portfolio 1958–1972, pp. 12–15; Terry Boyce, “Paragon of Excess: 1958 Buick Limited,” Special Interest Autos #53 (September-October 1979), reprinted in The Hemmings Book of Buicks, pp. 65-71; Johnny Boyd, “Johnny Boyd Tests the ’57 Buick,” Speed Age June 1957, reprinted in Buick Performance Portfolio 1947-1962, pp. 68–71; Arch Brown, “1957 Chevrolet Bel Air: The Really Hot One,” Special Interest Autos #96 (November-December 1986), reprinted in The Hemmings Book of Postwar Chevrolets, pp. 54-69; “Buick Builds a Better One,” Hot Rod March 1959, reprinted in Buick Performance Portfolio 1947-1962, pp. 92–95, 104; “Buick 1960,” Motor Trend Vol. 11, No. 11 (November 1959), reprinted in ibid, pp. 96–97; Jim Carroll, “’59 Buick on Trial,” Motor Trend Vol. 10, No. 10 (October 1958), reprinted in ibid, pp. 87-91; Charles S. Chapman, Jr., and Kenneth W. Gage, assignors to General Motors Corporation, “Transmission,” U.S. Patent No. 2,912,876, filed 20 May 1957, issued 17 November 1959; Chevrolet Engineering Center, Engineering Product Information Department, 1957 Chevrolet Engineering Achievements: Passenger Car Features (Detroit, MI: October 1956); Chevrolet Motor Division of General Motors Corporation, “Chevrolet 1957” [brochure, ca. October 1956]; “Chevrolet 1958: It Goes Big…With Spectacular New Shape!” [brochure, ca. October 1957]; 1958-1960 Chevrolet Turboglide Transmission: Construction and Operation (Detroit, MI: Chevrolet Motor Division, General Motors Corporation, May 1960); Gilbert K. Hause, assignor to General Motors Corporation, “Transmission,” U.S. Patent No. 2,919,608, filed 2 August 1956, issued 5 January 1960; Vincent Douglas, “1961 Impala: Big-Block Chevy, Family Style,” Special Interest Autos #147 (May-June 1995), reprinted in The Hemmings Book of Postwar Chevrolets, pp. 78–85; Tim Howley, “1959 Buick Electra 225 Convertible: Flash and Fins,” Special Interest Autos #126 (November-December 1991), reprinted in The Hemmings Book of Buicks, pp. 72-77; and “SIA comparisonReport: ’58 vs. ’59 Chevrolet Impala: What a Difference a Year Makes!” Special Interest Autos #140 (March-April 1994), reprinted in The Hemmings Book of Postwar Chevrolets, pp. 70–77; Oliver K. Kelley, assignor to General Motors Corporation, “Hydraulic Torque Converter,” U.S. Patent No. 2,882,684, filed 17 July 1956, divided 31 July 1957, issued 21 April 1959; and “Transmission,” U.S. Patent No. 2,964,976, filed 13 January 1958, issued 20 December 1960; Oliver K. Kelley and Gilbert K. Hause, assignors to General Motors Corporation, “Triple Turbine Bus and Truck Transmissions,” U.S. Patent No. 3,021,727, filed 13 October 1958, issued 20 February 1962; Oliver K. Kelley, Gilbert K. Hause, and Frank A. Swindell, assignors to General Motors Corporation, “Reactor Blade Pitch Control of a Hydro-Dynamic Torque Converter,” filed 6 March 1957, issued 10 November 1959; Richard M. Langworth, “Something Ventured, Nothing Gained: The Story of the 1957-58 Buick,” Collectible Automobile Vol. 17, No. 5 (February 2001), pp. 8–21; Mike Mueller and Anthony Young, Classic Chevy Hot Ones: 1955–1957 2nd ed. (Ann Arbor, MI: Lowe & B. Hould Publishers, 2002); “1958 Chevrolet Impala Road Test,” Motor Life January 1958, reprinted in Impala & SS Muscle Portfolio 1958–1972, pp. 5-7; Tom Sidoti, “1959 Buick Triple Turbine Transmission,” 1959 Buick Electra 225 Convertible, 20 October 2009, 1fine59. com/?paged=2, accessed 17 November 2015; “Testing the 60’s: Chevrolet V-8: Plushness…with a Price,” Motor Life February 1960, reprinted in Impala & SS Muscle Portfolio 1958–1972, pp. 21-22; “The 1959 Buick,” Motor Life November 1958, reprinted in Buick Performance Portfolio 1947-1962, p. 80–83; Jim Whipple, “Car Life 1958 Consumer Analysis: Buick,” Car Life Vol. 6, No. 3 (April 1958), reprinted in ibid, pp. 72–75; Frank J. Winchell and Oliver K. Kelley, assignors to General Motors Corporation, “Transmission,” U.S. Patent No. 3,008,349, filed 25 February 1957, issued 14 November 1961; and Walt Woron, “Chevrolet ’57,” Motor Trend Vol. 8, No. 12 (December 1956), reprinted in Chevrolet 1955-1957, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1988), pp. 64-68.

Additional information on Roto Hydra-Matic came from “Autocar Road Test 1908: Vauxhall Cresta Hydra-Matic 2,651 c.c.,” Autocar 11 January 1963, pp. 58–62; Terry Bebbington, “EJ-EH Holden History and Information,” Australian Classic Car December 2003; August H. Borman, Jr.; Charles W. Cline; and Carl E. Shellman, assignors to General Motors Corporation, “Transmission,” U.S. Patent No. 3,132,535, filed 20 September 1960, issued 12 May 1964; “Car Life Road Test: Oldsmobile F-85,” Car Life Vol. 9, No. 4 (May 1961), reprinted in Oldsmobile Automobiles 1955-1963, pp. 66-70; “Car Life Road Test: Oldsmobile 98 Holiday Sports Sedan,” Car Life Vol. 10, No. 3 (April 1962), reprinted in ibid, pp. 74-78; “EJ Holden,” “EK Holden,” and “Holden History,” Unique Cars and Parts [Australia], n.d., www.uniquecarsandparts. com.au, accessed 12 November 2015; Ken Fermoyle, “Buick, Olds, Pontiac Go Compact,” Popular Science Vol. 177, No. 4 (October 1960), pp. 72–76, 244–246; General Motors Continental, “Kapitän / Kapitän L” [Dutch brochure, ca. 1961]; General Motors-Holden Ltd., “Holden: Australia’s Own Car” [EK Holden brochure, 1961]; Walter B. Herndon, “GM develops light-weight, compact, Hydra-Matic transmissions,” The SAE Journal Vol. 69, No. 3 (March 1961), pp. 46–48; Walter B. Herndon and Howard E. Olsen, assignors to General Motors Corporations, “Transmission,” U.S. Patent No. 3,141,354, filed 8 March 1962, issued 21 July 1964; “Hydra-Matic 61-05 Transmission, Parts I and II,” Automobile Engineer Vol. 50, No. 15 (December 1960), pp. 524–31, and Vol. 51, No. 1 (January 1961), pp. 2–8; J.L. Spoormaker N.V., “Opel” [Dutch brochure], 1961; Oliver K. Kelley, Stanley L. Buckay, and Paul J. King, assignors to General Motors Corporation, “Balanced Inertia Plural Step-Ratio Transmissions,” filed 29 April 1955, issued 6 March 1962; “Olds F-85: Another Rocket Hits the Road,” Popular Mechanics Vol. 114, No. 4 (October 1960), p. 100–102, 310; Oldsmobile Division, General Motors Corporation, “F-85 by Oldsmobile” [brochure], February 1961; “Oldsmobile for ’64: Where the Action Is!” [brochure], September 1963; “’61 Olds” [brochure], October 1960; “’62 Oldsmobile” [brochure], September 1961; “’63 Oldsmobile” [brochure], September 1962; and “’64 Oldsmobile: Models • Equipment • Prices” [dealer literature], February 1964; “Oldsmobile Dynamic 88 Celebrity Sedan,” Car Life Vol. 10, No. 7 (August 1962), reprinted in Oldsmobile Automobiles 1955-1963, pp. 84-87; “Oldsmobile F-85,” Car and Driver Vol. 6, No. 11 (May 1961), reprinted in ibid, pp. 71-73, 100; “Oldsmobile F-85,” Motor Trend Vol. 13, No. 2 (February 1961), reprinted in ibid, pp. 61-65; Oldsmobile Mail List Server Community, “Transmissions,” Olds FAQ, 1996–2000, www.442. com/oldsfaq/ oftrn.htm, last accessed 15 February 2016; Pontiac Motor Division of General Motors Corporation, “Answers That Sell: 1964 New Product Facts” [dealer literature], 30 August 1963; “1961 Pontiac” [brochure, ca. September 1960]; “Come see our ’63 Pontiacs” [brochure, ca. October 1962]; and “Wide-Track Pontiac ’62” [brochure, ca. October 1962]; “Transmissions,” Popular Mechanics Vol. 115, No. 1 (January 1961), pp. 157–158; and Jim Whipple, “PM Owners Report: Nimble Olds F-85 Pleases Owners; Mileage, Transmission Draw Fire,” Popular Mechanics Vol. 120, No. 1 (July 1963), pp. 76–79, 196–197.

Additional information on the Corvair Powerglide and Pontiac TempesTorque came from Bill Carroll, “Inside Pontiac’s Terrific Tempest!” Sports Cars Illustrated Vol. 6, No. 4 (October 1960)) and “Pontiac Tempest Road Research Report,” Sports Cars Illustrated Vol. 6, No. 9 (March 1961), both reprinted in Car and Driver on Pontiac 1961–1975, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1986), pp. 5-16; Chevrolet Motor Division of General Motors Corporation, “Corvair by Chevrolet: The Prestige Car in Its Class” [1960 brochure], 1959; “Corvair Automatic Transmission (Road & Track Road Test 235),” Road & Track Vol. 11, No. 6 (February 1960), reprinted in Corvair Performance Portfolio 1959-1969, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1998), pp. 22–23; Ken Fermoyle, “Pontiac Tempest: Radical New Compact,” Popular Science Vol. 177, No. 3 (September 1960), pp. 53–58; Wick Humble, “1961 Pontiac Tempest: But cars aren’t supposed to have curved driveshafts,” Special Interest Autos #48 (November-December 1978), reprinted in The Hemmings Motor News Book of Pontiacs, pp. 74–86; Oliver K. Kelley, Kenneth W. Gage, and Richard W. Craig, assignors to General Motors Corporation, “Transmission and Swinging Drive Axles Including Torque Converters,” U.S. Patent No. 3,170,534, filed 7 January 1959, issued 23 February 1965; Karl Ludvigsen, “SCI Analyzes Ed Cole’s CORVAIR,” Sports Cars Illustrated Vol. 5, No. 5 (November 1959), reprinted in Corvair Performance Portfolio 1959-1969, pp. 5–13, 17; Jan P. Norbye and Jim Dunne, Pontiac 1946-1978: The Classic Postwar Years (Osceola, WI: Motorbooks International Publishers & Wholesalers, 1979); Pontiac Motor Division of General Motors Corporation, “1962 Tempest by Pontiac” [brochure, ca. October 1961]; “’63 Pontiac Tempest” [brochure, ca. October 1962]; and “Tempest: Quality Newcomer from Pontiac!” [brochure, ca. November 1960]; and Wayne Thoms, “Tempest Le Mans,” Motor Trend Vol. 15, No. 2 (February 1963), pp. 54–59.

Other background information came from Robert Ackerson, “1950 Packard DeLuxe Eight: The Last of Packard’s Postwar Pachyderms,” Special Interest Autos #64 (July-August 1981), reprinted in The Hemmings Motor News Book of Packards: driveReports from Special Interest Autos magazine, eds. Terry Ehrich and Richard Lentinello (Bennington, VT: Hemmings Motor New, 2001), pp. 58–65; Allison Transmission’s History-Heritage page at www.allisontransmission. com, accessed 13 October 2015; Oscar H. Banker, “Change Speed Planetary Transmission,” United States Patent No. 2,077,387, applied 16 July 1934, renewed 22 March 1935, issued 20 April 1937; Oscar H. Banker, “Transmission Mechanism,” U.S. Patent No. 1,795,465, filed 26 November 1928, issued 10 March 1931; Oscar H. Banker, assignor to Continental Illinois Bank and Trust Company, “Transmission,” U.S. Patent No. 1,795,464, filed 21 October 1927, issued 10 March 1931; “Transmission,” U.S. Patent No. 2,003,963, filed 21 March 1930, issued 4 June 1935; “Automatic Transmission,” U.S. Patent No. 1,843,193, filed 9 April 1930, issued 2 February 1932; “Automatic Change Speed Transmission,” U.S. Patent No. 1,843,195, filed 12 February 1931, issued 2 February 1932; “Automatic Clutch,” U.S. Patent No. 1,851,146, filed 20 March 1930, issued 29 March 1932; “Automatic Change Speed Transmission,” U.S. Patent No. 1,943,293, filed 24 July 1931, issued 16 January 1934; Oscar H. Banker, assignor to New Products Corporation, “Variable Speed Transmission,” U.S. Patent No. 1,937,503, filed 3 September 1931, issued 5 December 1933; “Clutch Mechanism,” U.S. Patent No. 2,042,454, filed 19 March 1932, issued 2 June 1936; “Automatic Change Speed Transmission,” U.S. Patent No. 1,996,790, filed 3 November 1932, issued 9 April 1935; “Change Speed Transmission,” U.S. Patent No. 1,985,884, filed 14 December 1932, issued 1 January 1935; “Planetary Transmission Mechanism,” U.S. Patent No. 2,005,726, filed 29 June 1933, issued 25 June 1935; “Change Speed Transmission,” U.S. Patent No. 2,077,387, filed 16 July 1934, issued 20 April 1937; “Clutch Mechanism,” U.S. Patent No. 2,104,014, filed 16 July 1934, issued 4 January 1938; “Automatic Transmission,” U.S. Patent No. 2,199,095, filed 13 October 1934, issued 30 April 1940; “Change Speed Transmission,” U.S. Patent No. 2,140,502, filed 30 November 1934, issued 20 December 1938; “Automatic Transmission,” U.S. Patent No. 2,171,534, filed 29 May 1935, issued 5 September 1939; “Automatic Transmission,” U.S. Patent No. 2,262,747, filed 18 September 1936, issued 18 November 1941, reissued 18 May 1943; and “Automatic Transmission,” U.S. Patent No. 2,237,297, filed 15 September 1937, issued 8 April 1941; Oscar H. 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Clarke (Cobham, England: Brooklands Books Ltd., ca. 1992), p. 78; Cadillac Motor Car Division, General Motors Corporation, “1966 Cadillac: New Elegance…New Excellence…New Excitement” [brochure], 1966; and “1968 Cadillac” [brochure], 1968; “Cadillac Series 60,” Car Life Vol. 11, No. 10 (November 1963), reprinted in Cadillac Automobiles 1960–1969, pp. 48–49; “Car Life Road Test: Buick LeSabre 400,” Car Life Vol. 12, No. 12 (January 1965), reprinted in Buick Muscle Portfolio 1963-1973, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 2001), pp. 33–37; “Car Life Road Test: Buick Skylark & Gran Sport,” Car Life Vol. 13, No. 3 (April 1965), pp. 45–50; “Car Life Road Test: Cadillac Sedan de Ville,” Car Life Vol. 12, No. 6 (July 1964), reprinted in Cadillac Automobiles 1960–1969, pp. 56–59; “Car Life Road Test: California GS,” Car Life Vol. 15, No. 5 (June 1967), reprinted in Buick Muscle Portfolio 1963-1973, pp. 70–74; “Car Life Road Test: GS 400,” Car Life Vol. 14, No. 12 (January 1967), reprinted in ibid, pp. 60–65; “Car Life Road Test: 1964 Buick Electra 225 Hardtop Coupe,” Car Life Vol. 12, No. 1 (February 1964), reprinted in Buick Muscle Portfolio 1963-1973, pp. 17-21; “Car Life Road Test: 1964 Oldsmobile Cutlass Holiday,” Car Life Vol. 11, No. 11 (December 1963), reprinted in Oldsmobile Muscle Portfolio 1964–1971, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1999), pp. 11–17; “Car Life Road Test: Oldsmobile Delta 88,” Car Life Vol. 13, No. 3 (April 1965), reprinted in ibid, pp. 33–37; Chevrolet Motor Division of General Motors Corporation, “Chevrolet Camaro” [brochure D-78776 R-1], 1969; “Chevy’s New Little Car Is Open for Business” [brochure 1102], ca. September 1970; “Discover all the facts and features about the beautiful full-size Chevrolet ’66” [brochure], 1965; “1940 Chevrolet: Special Deluxe, Master Deluxe, Master 85,” [brochure, ca. September 1939]; “1954 Chevrolet Advance-Design Trucks: For Loads of Value: [brochure 1,000 M], October 1953; “1971 Nova Coupe/Sedan/SS” [brochure 1144 R-1], January 1971; “’72 Nova. How to see less of your mechanic and more of America.” [brochure 1618], September 1971; “’74 Nova: Building a better way to see the U.S.A.” [brochure 2676], September 1973; “’74 Vega” [brochure 2677-Rev], January 1974; and “The Little Car That Does Everything Well” [Vega brochure 1619], September 1971; Allan Coats, “Rotary Power Transmission Mechanism,” U.S. Patent No. 1,760,480, filed 4 December 1925, issued 27 May 1930; and “Rotary Mechanism for Transmission of Power,” U.S. Patent No. 1,760,397, filed 18 November 1927, issued 27 May 1930; John Etheridge, “It’s White Tie & Tails for Chevy Caprice ‘396,’” Motor Trend Vol. 17, No. 6 (June 1965), pp. 48–53; Hermann Föttinger, “Flüssigkeitsgetriebe mit einem oder mehreren treibenden und einem oder mehreren getriebenen Turbinenräder zur Arbeitsübertragung zwischen benachbarten Wellen,” DRP Nr. 221422, filed 24 June 1905, issued 25 April 1910; Hermann Föttinger, assignor to Stettiner Maschinenbau AG ‘Vulcan,’ “Hydraulic Device for Transmitting Power,” U.S. Patent No. 1,199,359, filed 19 June 1906, issued 26 September 1916; “Transmission Device,” U.S. Patent No. 1,199,360, filed 26 January 1910, issued 26 September 1916; and “Transmission Device,” U.S. Patent No. 1,199,361, filed 26 January 1910, issued 26 September 1916; General Motors Corporation, “GM Powertrain: Past, Present, Future,” www.gm. com/experience/ technology/ gmpowertrain/ about/powertrain_history.jsp [now www.gmpowertrain. com], accessed 28 May 2010; “Golden Anniversary Packard Models,” The Motor 6 July 1949, reprinted in Packard Gold Portfolio 1946-1958, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1988), pp. 19–21; Tony Hogg, “Audi 5000 Turbo,” Road & Track Vol. 31, No. 9 (May 1980): pp. 62–64; Ari Holopainen, “Planetary Gears,” LUGNET News, 2005, www.lugnet. com/~3813/epicyclic, accessed 9 June 2017; Roger Huntington, “The Great Transmission Controversy: Coupling vs. Converter,” Car Life Vol. 10, No. 2 (March 1963), pp. 18–21, and “Turnpike Cruiser: Oldsmobile Designs a Long-Legged, Strong-Willed Gas Miser,” Car Life Vol. 14, No. 3 (April 1967), reprinted in Cutlass and 4-4-2 Muscle Portfolio 1964–1974, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1998), pp. 34–39; “Invicta Black,” Motorstown, n.d., www.motorstown. com/news/ 1091-invicta-black.html, accessed 15 October 2015; “Invicta Black Prince,” A to Z of Cars, Classic & Sports Car, 29 March 2011, www.classicandsportscar. com, accessed 15 October 2015; Invicta Car Development Co., “Invicta” [brochure, 1947]; Robert W. 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The typeface used in this article’s author-created tables, diagrams, and other graphics (and for the English-language captions we added to kamasko’s 2013 torque converter diagram in the sidebar on torque converters) is Liberation Sans, one of the Liberation Fonts (version 2.00.1 or later), which are copyright © 2012 Red Hat, Inc., used under the SIL Open Font License, Version 1.1. Liberation is a trademark of Red Hat, Inc. registered in U.S. Patent and Trademark Office and certain other jurisdictions. Red Hat is a trademark of Red Hat, Inc., registered in the United States and other countries.

Our inflation estimates came from the U.S. Bureau of Labor Statistics Inflation Calculator at data.bls.gov/cgi-bin/cpicalc.pl. Please note that inflation estimates are provided solely for readers’ general information; this is an automotive history, not a treatise on the historical value of money, and nothing in this article should be taken as financial advice of any kind!

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