The Hydra-Matic, GM’s first fully automatic transmission, was a great success, inspiring a host of rivals — including some within General Motors itself. This week, we look at the origins of Dynaflow and Powerglide, the ambitious but ill-fated Turboglide and Triple Turbine, the later controlled coupling Hydra-Matic and Roto Hydramatic, and more.
TORQUE CONVERTER DRIVE
As we saw in our first installment, Oldsmobile’s original Hydra-Matic, introduced in 1939, was the world’s first really successful fully automatic transmission. By 1952, GM had produced more than 2 million Hydra-Matics, which were used by Oldsmobile, Cadillac, Pontiac, and a variety of other automakers, ranging from Kaiser-Frazer to the short-lived Muntz Jet. Hydra-Matic was standard on Cadillacs by the early fifties and went into more than 80% of all Oldsmobiles and Pontiacs.
Notably missing from Hydra-Matic’s list of users were GM’s other automotive divisions, Chevrolet and Buick. Buick’s absence was particularly curious considering that the division had actually manufactured Hydra-Matic’s short-lived semi-automatic predecessor, the 1937-1939 Automatic Safety Transmission. Although corporate management had browbeaten Buick general manager Harlow Curtice and chief engineer Charles Chayne into offering the semi-automatic transmission in 1938, Buick’s engineers had never liked it and they liked Hydra-Matic even less.
There were several reasons for Buick’s disdain for Hydra-Matic, among them divisional pride. Some Buick engineers still resented the cancellation of the “Roller,” a friction-drive automatic they’d developed in the early thirties, which they felt was a superior transmission. They were also displeased with Hydra-Matic’s endemically jerky shifts. As we discussed in last week’s article, each of the H-M’s gear changes was mechanically complicated, involving a coordinated application and release of brake bands and clutch packs. Shifts were always firm, and if the transmission was not in perfect adjustment or if the bands were worn, it changed gears with a jolt. On Oldsmobiles and Cadillacs, which used open driveshafts, this could be mildly annoying. Buick and Chevrolet, however, used torque tube drive, which combined the driveshaft and axle into a single, rigid unit carried by the rear springs and connected to the transmission via a single universal joint. With a torque tube, each shift sent a pronounced thump through the frame and body, which Curtice and Chayne, in particular, considered unacceptable.
Even before Hydra-Matic went on sale, Detroit Transmission Division general manager Victor A. Olsen had concluded that there was no compelling reason all five of GM’s automotive divisions needed to share the same automatic transmission. The corporation would have to make a significant investment in additional plant capacity and tooling in any case; since Buick didn’t want Hydra-Matic and the new transmission presented various practical problems for Chevrolet (not the least of which was cost), why not design something better suited to those divisions’ respective technical and commercial needs?
That suggestion, surprisingly, came from engineer Oliver K. Kelley, who had been part of Earl Thompson’s corporate transmission group and played a major role in the development of Hydra-Matic. Kelley was intimately familiar with the Hydra-Matic transmission’s strengths and limitations; it worked, but it was not a particularly elegant design and there was considerable room for improvement.
Kelley had previously worked at GM’s Yellow Truck and Coach Manufacturing Company (which in 1943 would be rolled into GMC Coach in 1943) and was familiar with the work that division had done on torque converters; GMC had begun using Spicer two-speed torque converter automatics on some coaches back in 1938. A torque converter transmission, Kelley reasoned, could be made to provide torque multiplication equal if not superior to that of Hydra-Matic, but with considerably greater smoothness and much-reduced mechanical complexity, both of which would be of obvious benefit for Chevrolet.
The ramp-up of military production that preceded America’s entry into the Second World War soon shifted the focus of Kelley’s group away from passenger cars to an entirely different application: armored fighting vehicles (AFVs). While Cadillac would shortly adapt its V-8 engine and Hydra-Matic for use in light tanks, even twin automotive engines weren’t powerful enough for heavier armored vehicles and Hydra-Matic was ill-suited for those applications, handicapped by limited torque multiplication (first gear in prewar Cadillac Hydra-Matics was only 3.26:1), widely spaced gearing, and inadequate torque capacity.
As an alternative, Kelley’s group created an AFV version of the three-speed Torqmatic, a torque converter bus transmission manufactured by GM’s Allison Division. One of the principal applications of the new transmission was Buick’s new T-70 tank destroyer, which entered service in 1943 as the M-18 Hellcat. The Hellcat was powered by a nine-cylinder Continental R-975 radial engine with a monstrous net torque output of 940 lb-ft (1,275 N-m). Not only did the heavy-duty 900T Torqmatic have the torque capacity to withstand that output, which would have made a fine oily slush of the Hydra-Matic’s innards, the torque converter helped to keep the air-cooled Continental engine within its relatively narrow power band. The latter consideration was particularly important for tank destroyers, which relied on speed to make up for very limited armor protection; any momentary interruption of power was a potentially fatal problem.
The Torqmatic, which was also used in the M-39 armored utility vehicle and the M-26 Pershing medium tank, performed very well in arduous conditions. Its success eventually brought Kelley and company back to their original goal of applying those principles to automobiles. In November 1944, Kelley filed a patent application for an automotive torque converter transmission.
BUICK DYNAFLOW AND CHEVROLET POWERGLIDE
Even before the war was over, Kelley’s group built a number of test mules equipped with working prototypes of the new torque converter transmission. Although Kelley was still primarily thinking of Chevrolet, in mid-1945, he showed off one of the test mules to Charlie Chayne, who in turn convinced Buick general manager Harlow Curtice to test-drive it. The torque converter automatic was much more to Chayne and Curtice’s liking than Hydra-Matic had been, offering seamless (if rather stately) progress reminiscent of Buick’s abortive “Roller” transmission, an infinitely variable friction drive unit that had been canceled back in 1934 after extensive (and very expensive) development.
Buick powertrain engineer Rudolf J. Gorsky was ordered to work with Kelley’s corporate engineering group to develop a production version of the torque converter transmission for Buick. After extensive testing, the option was finally announced in January 1948 for the top-of-the-line Buick Roadmaster.
Buick’s new transmission, dubbed Dynaflow, took the torque converter drive concept a step further than had the wartime Hellcat. Although it used two planetary gearsets, providing two forward ratios plus reverse, Dynaflow did not actually shift gears automatically. In Drive, it instead relied on the torque multiplication of its complex, five-element torque converter. To expand its useful range of operating speeds, the converter used two impellers and two stators, each with a different blade pitch. At stall, it provided a maximum torque multiplication of 2.25:1, not far from the 2.39:1 first gear of Buick’s standard manual gearbox. As engine speed increased, the converter multiplication gradually faded; at cruising speed, both stators freewheeled and the converter acted like a conventional fluid coupling. In effect, Dynaflow was what we would now call a continuously variable transmission, although unlike modern belt/chain/roller-driven CVTs, its operation was purely hydraulic.
Dynaflow provided unparalleled smoothness with none of the four-speed Hydra-Matic’s distinct shift points. The consequence was lethargic low-speed throttle response. Unlike a mechanical reduction gear, the torque converter produced useful multiplication only at certain speeds. If you caught it outside that optimum range, stabbing the throttle produced more churning than forward motion, even with the 276 lb-ft (373 N-m) gross torque output of Buick’s biggest straight-eight engine. Slippage was also high, which resulted in heavy fuel consumption. Buick tried to compensate for the latter by using a taller (lower numerical) axle ratio with Dynaflow, but that did nothing for performance.
There was a ready cure for Dynaflow’s mediocre acceleration: manually selecting Low range added a 1.82:1 mechanical gear ratio to the converter’s multiplication. Low could be held to about 45 mph (72 km/h), providing much snappier takeoffs and stronger passing response. Unfortunately, the transmission had no way to shift automatically into high; the driver had to move the selector back to Drive and doing that too frequently tended to damage the clutches and bands. Buick’s owner’s manual cautiously described the low gear as “emergency low.”
Despite those shortcomings, Dynaflow was well-suited to the character of postwar Buicks, which emphasized refinement and comfort over performance or road manners. The average Buick buyer was not terribly concerned with fuel economy and welcomed Dynaflow’s lazy smoothness. It was too bad that Buick no longer offered limousines; Dynaflow lent itself admirably to a processional pace.
Dynaflow was followed in 1950 by Chevrolet’s Powerglide. Powerglide was a variation on the Dynaflow theme: conceptually similar, but differing in detail. Its greatest novelty was a second, smaller fluid coupling, mounted inside the five-element torque converter; the smaller coupling provided additional engine braking for descending steep grades without overheating the brakes.
Powerglide suffered the same limitations as the Buick transmission, which were more pronounced with Chevrolet’s six than with Buick’s eight. Powerglide-equipped Chevys came with a bigger, more powerful engine, but the new automatic added more than seven seconds to 0-60 mph (0-97 km/h) times and resulted in less-than-frugal fuel economy.
HYDRA-MATIC VERSUS DYNAFLOW
We may take it as a sign of GM’s considerable wealth and resources that it entered the fifties with three distinct automatic transmissions while most of its competitors were still struggling to develop even one. Until the debut of Chrysler’s two-speed PowerFlite in 1953, the only other automaker to develop its own automatic was Packard, which had introduced its torque converter Ultramatic in 1949. (GM, not convinced that the venerable independent had the resources for such a feat, later sued Packard, claiming Ultramatic’s torque converter design infringed on Buick’s patent.) Both Studebaker and Ford turned to Borg-Warner to develop their first automatics, while most of the other independents either bought Hydra-Matic or went without.
In a later era, GM’s corporate management would undoubtedly have pushed for standardization, but in the early fifties, General Motors controlled nearly half of the largest automotive market in the world and allowing the divisions to remain independent and competitive was an affordable indulgence. Just as important was the fact that GM had invested considerable capital in development and tooling for Hydra-Matic, Dynaflow, and Powerglide, which the corporation was not about to casually discard.
Moreover, the divisions’ customers were developing strong feelings about the pros and cons of each transmission, which sometimes resembled the rivalry between competing sports franchises. Hydra-Matic fans extolled its efficiency and crispness; Dynaflow supporters proclaimed the virtues of that transmission’s seamless action, and derided Hydra-Matic’s lurching shifts. Even the chief engineers of Oldsmobile and Buick exchanged good-natured jibes about the comparative merits of “Dyna-Slush” and “Hydra-Jerk,” although the latter camp had to swallow their pride for a while in 1953, when the destruction of the Livonia Hydra-Matic plant briefly forced Olds and Cadillac to use Dynaflow. The irony is that both transmissions emerged from the the same group in the corporate Engineering Staff; browsing through GM’s transmission-related patents from this period reveals many common names and evidence of similar design methodology.
Other manufacturers quickly settled on a compromise — two- or three-speed planetary gearsets combined with a torque converter. Chevrolet went that route in 1953, reengineering Powerglide to start in low and shift automatically to high; Packard adapted Ultramatic to do the same late in the 1954 model year. Instead, GM’s engineering staff spent the next decade refining the Dynaflow and Hydra-Matic concepts.