Dynaflow, Turboglide, Roto Hydra-Matic, and Other Early GM Automatics

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 trade name “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 61-05) 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 around 25 lb (11 kg) heavier than the smaller version, had greater torque capacity, and used fractionally taller (lower numerical) indirect ratios, but the two units functioned identically.

1961 Oldsmobile Super 88 hardtop front 3q © 2008 Aaron Severson
While Pontiac retained the earlier dual-coupling four-speed Hydra-Matic (now dubbed “Super Hydra-Matic”) for the division’s biggest cars, Oldsmobile switched entirely to the new three-speed units for 1961. Hydra-Matic was nominally optional on Oldsmobile Super 88s like this two-door Holiday coupe, but very, very few contemporary Oldsmobiles were built with manual gearboxes.

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 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.

Color diagram of 1961–1964 Roto Hydra-Matic transmission © 2016–2017 Aaron Severson
The three-speed Hydra-Matic’s torque converter was based on the smaller second coupling of the four-speed Controlled Coupling Hydra-Matic and could be emptied and filled in the same manner. The converter was empty in second gear (whether in Drive or Super/D-Right) and full in all other gears, including neutral and reverse. This diagram again is not to scale (proportionally, the converter is even smaller than this) and has been simplified in the increasingly vain hope of visual coherence. (Author diagram)

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. 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.

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 rigidly affixed to the carrier shaft, it always rotated at the same speed as the driveshaft and could turn in either direction.

Color diagram of 1961–1964 Roto Hydra-Matic transmission reaction members and clutches © 2016 Aaron Severson
In the three-speed Roto Hydra-Matic, the torque multiplier (green) was rigidly attached to both planet carriers, which were attached to the output shaft. This was marginally beneficial in reverse, but greatly limited the torque converter’s ability to provide useful torque multiplication in any forward gear. In September 1963, Jack Qualman applied for a patent (issued as U.S. Patent No. 3,270,584) on a revised layout that would have given the torque multiplier a conventional one-way clutch while divorcing it from the carrier shaft, but that solution was never implemented in production. (Author diagram)

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. If the selector was in 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.

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.) 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.

Color diagram of 1961–1964 Roto Hydra-Matic transmission reaction members and clutches © 2016–2017 Aaron Severson
As in the earlier Controlled Coupling Hydra-Matic, Roto Hydra-Matic’s neutral clutch served to anchor the outer race of a one-way sprag clutch to the transmission case. However, in the three-speed Hydra-Matic, the front sun gear and rear annulus were permanently interconnected, allowing both gearsets to share a single sprag clutch and a single overrun brake. (Author diagram)

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 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 (disabling the sprag clutch), 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.

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.

1961 Oldsmobile Dynamic 88 convertible dashboard © 2009 Aaron Severson
Oldsmobile adopted the three-speed Hydra-Matic for both the compact F-85 and for 1961-1964 Eighty-Eight and Ninety-Eight models, like this 1961 Dynamic Eighty-Eight. Pontiac used Roto Hydra-Matic for the Catalina, Ventura, and Grand Prix, but for some reason opted to retain the dual-coupling four-speed automatic (now called Super Hydra-Matic) for the big Star Chief and Bonneville through 1964. Cadillac never used Roto Hydra-Matic, staying with the four-speed Hydra-Matic until switching to Turbo Hydra-Matic in 1964–1965.

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, some 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 were far from ideal. Despite the torque multiplier and a rather short first gear (2.97:1 for the big units, 3.03:1 for the lighter-duty model), starting ratios, at 3.56:1 or 3.64:1 respectively, 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 (1.56:1 or 1.58:1 and direct drive respectively) were closer to third and fourth in the dual-coupling Hydra-Matic. (The torque multiplier was ineffective in second and could not provide any torque multiplication in third.) 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” (whose origins are described in our article on the Imperial): 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.

1963 Buick Riviera front 3q © 2008 Aaron Severson
The 1963 Buick Riviera used Buick’s older twin-turbine transmission — now called simply Turbine Drive — but the 1964 model was one of the first users of the new Turbo Hydra-Matic three-speed transmission, which Buick called Super Turbine 400.

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, 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 trade 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.

# # #


AUTHOR’S NOTE

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

NOTES ON SOURCES

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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. 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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; 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. Mooney, Jr., assignors to General Motors Corporation, “Transmission,” U.S. Patent No. 2,929,270, filed 7 March 1957, issued 22 March 1960; U.S. Department of the Army, Principles of Automotive Vehicles (Department of the Army Technical Manual TM 9-2700) (Washington, DC: U.S. Government Printing Office, November 1947); Jim Whipple, “Buick Special’s performance-plus economy,” Popular Mechanics Vol. 115, No. 3 (March 1961), pp. 122–125, 286–291; and “PM’s 1000-Mile Road Test of Buick’s New V-6,” Popular Mechanics Vol. 116, No. 4 (October 1961), pp. 108–111, 258–260; ‘woodbox’ and ‘Buickspec6231,’ “1963 Skylark Dynaflow trans help required,” Team Buick, 20 November 2011, www.teambuick. com/ forums/ showthread.php?20995-1963-Skylark-Dynaflow-trans-help-required/, accessed 21 February 2016; and Jim Wright, “A Wildcat from Buick,” Motor Trend Vol. 14, No. 8 (August 1962), reprinted in Buick Performance Portfolio 1947-1962, pp. 136-140, and “Chevrolet Impala SS 250 H.P. 340 H.P.,” Motor Trend Vol. 15, No. 3 (March 1963), reprinted in Impala & SS Muscle Portfolio 1958–1972, pp. 48–53.

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 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; 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; 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. 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. 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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; the Internet Archive (archive.org); “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. Irwin, “GM’s New 3-Speed Automatic Transmission,” Motor Trend Vol. 20, No. 9 (September 1968), pp. 44–45; Achim Leutz’s Hermann Föttinger website, hermann-foettinger.de, last updated 2014, accessed 24 September 2015; Patrick Lindemann, Markus Steinberger, Thorsten Krause, iTC, “Innovative Solutions for Torque Converters Pave the Way into the Future,” Schaeffler Symposium 2014 (Schweinfurt, Germany: Schaeffler Technologies AG & Co. KG), pp. 280–301; “Lost Marques: Invicta,” Unique Cars and Parts, www.uniquecarsandparts. com.au/ lost_marques_invicta.php, accessed 15 October 2015; Bob McVay, “Road Testing the Oldsmobile Jetstar 88,” Motor Trend Vol. 16, No. 4 (April 1964), reprinted in Oldsmobile Muscle Portfolio 1964–1971, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1999), pp. 5–10; Donald E. 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You’ve got a new choice. 1964 Wide-Track Pontiac Tempest.” [brochure, ca. Octber 1963]; “Nineteen Sixty Five Pontiac” [brochure, ca. October 1964]; “1972 Pontiac” [brochure DM 26627], August 1971; “Pontiac 1973” [brochure], August 1972; “Pontiac ’69” [brochure], October 1968; “Pontiac’s 70’s” [brochure DM 27229], September 1969; “Pure Pontiac” [brochure DM 29103], August 1970; Arthur Pound, The Turning Wheel: The Story of General Motors Through Twenty-Five Years 1908–1933 (Garden City, NY: Doubleday, Doran & Co., Inc., 1934); “Q&A: dangling definitions,” Motor Trend Vol. 20, No. 7 (July 1968), p. 102; Carlton R. Radcliffe, “Hydraulic Power Transmitting Apparatus,” U.S. Patent No. 1,576,996, filed 3 August 1920, issued 16 March 1926, and “Hydraulic Power Transmitting Apparatus for Motor Vehicles,” U.S. Patent No. 1,667,565, filed 24 April 1917, issued 24 April 1928; Pol Ravigneaux, “Speed Changing Device,” U.S. Patent No. 2,220,174, filed 22 August 1936, issued 5 November 1940; “Speed Changing Device,” U.S. Patent No. 2,194,954, filed 10 October 1937, issued 26 March 1940; “Gear Box With Free Wheeling Gear,” U.S. Patent No. 2,195,783, filed 29 December 1937, issued 2 April 1940; “Variable Speed Gear,” U.S. Patent No. 2,239,973, filed 7 July 1938, issued 29 April 1941; “Epicyclic Change-Speed Gear,” U.S. Patent No. 2,631,476, filed 22 July 1950, issued 17 March 1953; and “Epicyclic Change-Speed Gear,” U.S. Patent No. 2,761,333, filed 24 March 1952, issued 4 September 1956; Bill Sanders, “Now You Can Have It Too: Econoperforleration* (*Economy, Performance, Acceleration): Oldsmobile Has Added It for 1968,” Motor Trend Vol. 20, No. 7 (July 1968), pp. 94–97; Steve Simpson, “Corvair Among Coconuts,” Modern Motor September 1961, reprinted in Corvair Performance Portfolio 1959-1969, pp. 36–38, 48; R.P. Stevenson, “British Cars – Mechanical Marvels,” Popular Science Vol. 150, No. 6 (June 1947), pp. 158–162; Summit Racing, “Torque Converter Selection – Summit Racing Quick Flicks,” YouTube.com, 6 April 2012, https://www.youtu.be/j5JFMs8gdbs, accessed 23 September 2014; “The Hydraulic Torque Converter,” Rail Motor Society, n.d., www.railmotorsociety. org.au/ rm_trans_htc_page.htm, accessed 13 October 2015; “The Motor Road Test No. 16/56 (Continental): The Packard Clipper,” The Motor 27 June 1956, reprinted in Packard Gold Portfolio 1946-1958, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1988), pp. 142–145; Mark Theobald, “Yellow Coach,” Coachbuilt, 2004, www.coachbuilt. com, accessed 8 October 2015; Vincent Tocco, Jr., “Fluid Drive History,” American Blower, n.d., americanblowercorp. com, accessed 15 May 2010; Hans Tore Tangerud’s Autoblog website (www.lov2xlr8.no); U.S. War Department, Ordnance Maintenance: Ordnance Engine Model 975-C4 (Continental) (War Department Technical Manual 9-1725) (Washington, DC: U.S. Government Printing Office, 27 January 1944), and Ordinance Maintenance: Ford Tank Engines (Models GAA, GAF, and GAN) (War Department Technical Manual TM 9-1731B) (Washington, DC: U.S. Government Printing Office, June 1945); Vulcan Werke Hamburg, Stettiner Maschinenbau Actiengesellschaft, “Flüssigkeitsgetriebe zur Arbeitsübertragung zwischen benachbarten Wellen mittels treibender und getriebener Turbinenräder” DRP Nr. 238804, filed 24 June 1905, issued 30 September 1911; Ron Wakefield, “1970 Camaro & Firebird: Chevrolet & Pontiac versions of a new American GT, plus a facelifted Corvette for 1970,” Road & Track Vol. 21, No. 7 (March 1970), reprinted in Firebird and Trans-Am Muscle Portfolio 1967–1972, ed. R.M. Clarke (Cobham, England: Brooklands Books Ltd., ca. 1998), pp. 92–95; Alan Wenbourne, “Ravigneaux Planetary Transmission,” South East London Meccano Club, 2006, www.selmec. org.uk/ article_0001_ ravigneaux_planetary_transmission.aspx, accessed 11 October 2015; “Wilson, Charles E.,” Generations of GM History, GM Heritage Center, n.d., history.gmheritagecenter. com/ wiki/ index.php/ Wilson,_Charles_E., accessed 8 November 2015; and Frank J. Winchell, Jerry R. Mrlik, John E. Mahoney, Jack W. Qualman, Thomas R. Zimmer, and August H. Borman, assignors to General Motors Corporation, “Transmission and Control System,” U.S. Patent No. 3,321,056, filed 12 December 1963, issued 23 May 1967.

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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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103 Comments

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  1. Hey,how come you can yack all day long about this ones gearset setup,or that ones turbine combination,but no illustrations???
    Just because you can picture the entire mechanical world with words doesn’t mean the rest of humanity can.
    Pictures Please!!!!

    1. Um, no “Thank you for an awesome article and site?”

      There is an illustration of a Turboglide and it’s hardly fair to expect Aaron to write an great article about the development of the automatic AND delve into all the technical details. He does to a degree, but that’s not the overwhelming emphasis of the site, as far as I understand it.

      How about Googling “Turboglide,” “Dynaflow” or “Powerglide?”

    2. (ETA May 30, 2016): Very late, but there are now diagrams! I’m not a technical illustrator by any stretch of the imagination, but you can at least get a sense of how these things were laid out.

      1. There’s a site here that has a diagram of an overhaul of the controlled coupling hydra-matic. I can really see why GM wanted to get way from this design. Although today’s ZF 8 and 9 speeds are probably worse, but then half of the world industry is sharing the development costs for these.

        1. …And yet, they were damn near indestructible. We had a ’58 Pontiac that took a lot of punishment in the snow, yet worked without any issues, other than a small oil leak, until I had to sell it in late 1964.If I remember correctly, it was cast iron and weighed around 225 lbs.

          1. The ’58 edition weighed about 240 lb. GM was able to trim about 10-11 lb for 1960 by slimming down the case a bit.

  2. In the photo of the Hydra-Matic shift quadrant in the ’50 Olds 88, is that an aftermarket turn signal unit? If so, it’s a reminder of how times have changed! I understand that at that time, a heater was an option on many cars.

    1. I believe turn signals were standard on Oldsmobiles by 1949, at least on DeLuxe models. I’d need to find somebody with an Olds dealer book from that period to know for sure, but my information suggests they were standard fit.

      Pretty much everything [i]else[/i] was at least technically optional at that point, including oil filters, wheel covers, hood ornaments, windshield washers, and (at least until after the war) reversing lamps. Heaters didn’t become standard even on Cadillacs until almost the mid-fifties, and they weren’t standard on cheap cars for another decade after that. Very few cars were built without a lot of these items, but they weren’t included in the list price for many years.

  3. At least they did not charge extra for chrome after the war.

    I remember seeing a ’50s car ad that mentioned the [i]reverse[/i] gear was an optional extra. On the other hand many cars (particularly British) came with leather seats only because it was cheaper than vinal.

    1. I don’t know of any cars that late that didn’t come with a reverse [i]gear[/i], although reversing [i]lamps[/i] were still extra on many inexpensive cars at that point. Turn signals, as well.

    2. Just as well they didn’t charge extra for chrome.
      The ’58 Buicks & Olds would have cost a small country to buy.

      Back on topic, thank you once again for an
      entertaining read.

      Cheers,
      Chris

      1. Well, in essence, they did charge extra for the chrome, though fortunately not by the pound. On most cars of that era the amount of brightwork was tied to the trim level, and naturally the higher the trim level, the higher the price. Beyond that, there were often extra-cost dress-up packages (either factory- or dealer-installed) that primarily consisted of additional chrome trim. Such things didn’t really disappear from American options lists until the rise of Japanese-style tiered equipment packaging quite a few years later.

    3. Ahh! Those were the days! Everything from a Roller (that’s Rolls Royce to you Yanks) to a Moggy (Morris Minor) with a leather interior. I remember the smell well as a small child in the early ‘sixties.

      Unfortunately British manufacturers did make the switch to vinyl during that decade for economy reasons and every non-luxury car came with a ghastly black vinyl interior that was composed of shiny paper-thin crap. On hot days (mercifully few and far between in the UK), first degree burns to your back and ass were the minimum you could expect. No wonder parts counters did a roaring trade in textile seat covers — they may have been ugly, especially the furry ones, but sure beat the OEM’s one and only offering of black vinyl by the acre.

      I owned a 1966 Pontiac Bonneville 4-door for a short while in 1979-80 (I sold the engine and transmission to a local drag racer and scrapped the body because it was too rusty to repair). It was white with a turquoise interior (even the steering wheel was see-through turquoise perspex). The upholstery was Morrokide and that was a revelation to me. It just shouted quality and put into stark perspective just how short-changed we Europeans were when it came to cars, forced to pay over the odds for inferior rubbish. The only way to go lower was to buy something from the Soviet Block — not that a Lada or a Yugo could possibly be worse than a Hillman Avenger (Plymouth Cricket in the US). [Aside: Thanks a bunch Chrysler. You took over the Rootes Group, at the time manufacturers of the Sunbeam Tiger, and turned them to manufacturing the most embarrassing pile of dross in automotive history. Shite is shite regardless of whether you brand it as Hillman or Chrysler or Talbot, as happened to the Avenger over its lifespan.]

      Did things get better in the ’70s and ’80s? Not unless you consider flimsy Dralon “better”. As I recall, you purchased a car new paying extra for the “luxury” option and well before it got to five years old the upholstery was torn and stained and looked like a pigsty. I still get nostalgic for that old Pontiac — The body may have been a rust bucket but the interior was palatial.

  4. Thanks for a great website and particularly for the GM transmissions articles. Every article I’ve read has been complete, accurate, and very interesting.

  5. Thank you for the automatic transmission article(s) on GM. Finally, someone has accurately chronicled the myriad development story for us.
    Your site is a valuable and entertaining resource – keep up the great work!

  6. This brought back some memories – I remember when I first got my license driving my Dad’s ’65 Olds F-85 with Jetaway and those 1-2 shifts at about 70mph if you held your foot in it. I have a question – I have an childhood memory of an early 50’s vehicle ( think it was a Chevy ) with a “Torque-Glide” logo on the trunk lid instead of “Power-Glide”, but that can’t be right, can it?

    1. Chrysler had a number of semi-automatics in that period with a variety of bizarre names: Gyro-Torque, Fluid Torque Drive, Fluid-matic, Fluid-Drive, and Plymouth’s Hy-Drive. Maybe it was one of those?

    2. Actually, from 1965 up, the F-85, Buick Skylark, and Pontiac Tempest all utilized the newly available Turbo-Hydramatic 300, which in essence was the same thing as a Powerglide, but with non-interchangeable parts. Early versions had variable pitch and a rear pump. It was with the advent of these new automatics that the shift indicators from that time forward would read P R N D L.

      1. The latter point is correct, but the rest is not. As the text explains, the two-speed transmission used on 1964-on B-O-P A-bodies is not Powerglide, although they’re similar in many respects. Although the two-speed (which Buick called Super Turbine 300) was manufactured by Hydra-Matic Division, it was not called Hydra-Matic. (I know the source you’re looking at, and it’s incorrect.) The three-speed Turbo Hydra-Matic became optional in 1967 with the big engines only and was later supplemented by the medium-duty TH350. The two-speed remained available on low-end models into the early seventies.

        1. You are wrong the turbo 400 was built by the Buick division of GM in1964 and all divisions but Cheyenne used them in full size cars. I have a GM delve that is 3 inches thick telling how to rebuild every automatic transmission they used from 1956 to 1964 with service bullion so from Buick staring in
          1964 I used for 45 years in the transmission business

          1. At least some early TH400s and later TH350s were indeed built by Buick rather than Hydra-Matic Division, that’s true. (My assumption is that it was in part a retooling issue, since Hydra-Matic was still building substantial numbers of other designs, including Roto Hydra-Matic and limited numbers of the four-speed dual-coupling unit.) And some non-Buick users did indeed switch to TH400 for some models in 1964, although not all and not as widely as in 1965. (I assume by “Cheyenne” you mean “Chevrolet,” which first offered TH400 on B-body cars with the Turbo-Jet big blocks in mid-1965.)

            I’m familiar with the type of service manual you’re describing; I may even have referred to the same one you have. While manuals like that are handy from a technical standpoint, they aren’t ideal historical sources, which of course isn’t their function. Their technical information may be more or less correct at the time it was originally written (although it’s not altogether uncommon to find errors in that as well), but manuals like that often don’t do a great job of reflecting running production changes and the intricacies of what was offered on what model/in what combination and when are beyond their scope.

  7. anyone have a diagram of the dual path? It stopped shifting from low into second and I found a spring in the bottom of the pan. Where does it go?

    1. Sorry, I’m not qualified to give repair advice. You might try seeing if your local library has a service manual for it — I was able to find a copy of the Pontiac dual-coupling Hydra-Matic shop manual that way.

    2. Try this… as good an explanation of your problem as I’ve ever understood: https://www.youtube.com/watch?v=rLDgQg6bq7o

      1. He talks about your differential girdle spring at starting at ~1:10. It’s supposed to be hooked onto the upend of the gramys.

  8. [quote=steve dill]anyone have a diagram of the dual path? It stopped shifting from low into second and I found a spring in the bottom of the pan. Where does it go?[/quote]If you could provide a picture of the spring, I could look it up in my various manuals and give you an answer.

  9. I have a 62 Buick,Skylark,with the dualpath Tranny.the trans is in direct drive,only goes foward,no neautral,park orreverce,is thier a fix for this.

    1. Can some one HELP.
      I have a 1962 Olds Cutlass F 85, Auto Hydro Matic floor shift.
      I had the transmission rebuilt 3 times already.
      and the problem is that when the car warms to operating temp
      it starts to jerk and gos into neutral. it clears once i accelerate.
      RPMs Are normal. trans just dosnt stay in low gear when moving at 10mpg or at a stop. Thanks- Robbe California

      1. @Robert: I’m afraid I’m not at all qualified to offer repair or troubleshooting advice — sorry!

  10. this article was great. It answered my question as to why the 52 Super I just inherited doesn’t shift….that would be because it isn’t made to shift automatically….I read a blog online saying
    1952 Buick – the slowest car I ever loved….so true!

  11. anybody know where I can buy the flexible black fresh air vent tubes? Darn Mice

  12. Are the dyno-flow and power glides enter change able? With other motor?

    1. Well, there’s an old saying to the effect that you can make anything fit if you have a big enough hammer. I honestly don’t know how much trouble would be involved in interchanging them, but since they were never designed to be used behind the same engines or in the same cars, I imagine it would take some work.

      At one time, Buick Nailhead engines were popular with drag racers, so if you were asking this question in, say, 1964, there might have been aftermarket kits to mate an older Buick V-8 with a beefed-up Powerglide. (Some drag racers used Powerglide because it consumed relatively little power and they didn’t need a lower first gear.) Today, I suspect you’d have more luck finding some way to put in a Turbo Hydramatic. I’ve never looked, though.

      This is a question that would probably be best put to a performance transmission manufacturer or a shop that specializes in parts for older transmissions.

    2. No the dynaflow and the powerglide are not interchangeable. the dynaflow is about three times heavier and will not fit up to any engine that was made for the powerglide. The powerglide came in two models first being the cast iron model that was used through 1954 then the aluminum powerglide after that. both very good transmission, and easily rebuildable.

      1. The earliest Powerglide is very similar to the early Dynaflow, although I doubt they’re easily interchangeable. As the revised text explains, Powerglide had several phases: the early dual-impeller variety, used through 1952; the later iron-case version with a three-element converter, used, with various evolutionary changes, from 1953 to 1962–1963; and the late aluminum-case version. The aluminum Powerglide (for RWD cars — all Corvair Powerglide units had an aluminum case) was introduced for some models in 1962 and for others in 1963.

  13. chevy had 2 auto transmissions in 61and62 1 was a turbo glide the other was –glide that changed by fluid. there was no gears in the trans. on the gear selector was P R D G G was for grade as going up a hill. what was the name of that trans?

    1. The two transmissions were Powerglide and Turboglide. Powerglide was the familiar two-speed-plus-torque-converter Chevrolet automatic, while the transmission you’re thinking of was Turboglide, which is described in the text.

      The G position was for Grade Retarder. It was intended not for climbing hills, but for descending them; it was supposed to mimic the effect of engine braking, of which the Turboglide otherwise didn’t allow very much. The Grade Retarder was not useful for acceleration or hill climbing, although some people had problems because they assumed it worked like the Low position on Powerglide, which was definitely not the case!

  14. Re read this as a refresher on the development of the automatic. Thank you again. Your site is an invaluable resource and I cannot thank you enough for doing what you do.

  15. Thank you for your clear and concise explanation of Dynaflow, and how it differs from the other two GM automatics. As we were a “Buick family,” the innate superiority of Dynaflow was never a question; it was an article of faith. I remember the feelings of incredulity and betrayal I felt when I was told for the first time that Dynaflow was “Just Powerglide with a different name,” and that Hydramatic was obviously better, because Olds and Cadillac used it. You have restored my faith in Dynaflow.

  16. We have recently inherited a 53 Roadmaster. I think it is an early model serial #26854377 because the 322 nailhead has a weighted pully instead of a rubber loaded harmonic balancer. The Dynaflow is now in the transmission shop and we are finding puzzles. According to the shop manuals the 53 should be the new twin turbine with only 1 pump and one stator. This trans has the words “twin turbine” cast into the bellhousing. But inside it has 2 pumps and 2 stators. Do we have a transitional factory job or a trans shop hybrid? Was the change made to save money (fewer parts) or to improve performance? Will our new Roady rise and fly?

  17. Fascinating info.

  18. Hi can any body help me
    I have a 1958 Buick Road Master fitted with a Dynaflow Flight Pitch
    gear box can any one tell me where i can get spares for the gear box
    and will ship them to England

    1. I’m not able to help with technical issues or buying parts — sorry!

  19. Just wanted to say this is a great article. I started out looking to find the difference between the hydra-matic dual range and the strato-flight and wound up learning a lot more.

  20. The article refers to the Hydramatic’s jerkiness. Actually, many Hydramatics were so smooth that you could not even feel the shift; you could just hear the drop in engine speed. I remember in 1959 riding in a 1949 Lincoln with Hydramatic; it accelerated quickly and so smoothly that I could not feel the shifts. The same was true with some other cars with Hydramatic in which I rode, including a 1950 Pontiac, and those were all before GM introduced the Hydramatic with the second (controlled) fluid clutch in 1956. On the other hand, I rode in a 1953 Cadillac with had very firm shifts.

    The downshift resulting from flooring the accelerator were another matter; they were always accompanied by a mechanical clunk.

    1. The issue with the original Hydra-Matic was that because its shifts were mechanically complex (particularly between second and third, which was the most complicated sequence), its smoothness depended a great deal on how well the bands were adjusted, the condition of the transmission fluid, and other maintenance- and condition-related factors. If everything was perfectly adjusted, it would be quite acceptably smooth (particularly by the fifties, by which time GM had made a lot of minor refinements). If not, it would throw off the shift timing just enough to make the shift jerky, albeit not necessarily enough to really impair the transmission’s function. I suspect a lot of owners who complained to their dealers or mechanics were told, “Ehh, they all do that.”

      Even some of the engineers who originally designed the Hydra-Matic thought it was too complicated for its own good, which is why they subsequently got into the torque converter automatics, which didn’t shift at all. The original Dynaflow was very much the antithesis of the Hydra-Matic in a lot of these respects.

    2. My experience with Hydromatic cars was that they were fairly smooth in shifting. PowerGlide cars had a very pronounced jerk when shifting. When my city purchased GM buses in the sixties, the Hydromatic was very rough when shifting with an easily heard lowering in engine sound as speed increased.

      1. The difficulty with making blanket statements in this area is that each of these transmissions was around for a long time in several quite distinct versions, not all of which felt or acted the same.

        As the text explains, early Powerglide cars did not provide any automatic shifting in Drive, relying on torque converter multiplication exclusively. Powerglide was revised in 1953 to start in first and shift automatically to second. So, early Powerglides (or Dynaflow) were smoother than even a well-adjusted early Hydra-Matic, albeit not especially quick or efficient. After that, there were early (iron-case) and later (aluminum-case) Powerglide transmissions, tuned in different ways for different engines.

        Similarly, the early (1940 to 1955) and late (1956-1964 dual-coupling) Hydra-Matics were significantly different mechanically — albeit still related — and felt quite different.

        So, while it may sound pedantic, it’s important to qualify statements like, “X was smoother/rougher than Y.”

      2. Those GM buses had a 1 speed automatic Allison transmission. Great roaring noises as the variable torque converter changed pitch and allowed the bus to gradually accelerate to 25 mph, then an almighty clonk as the torque converter was locked-up with a mmm-uhh-mmm vibration that gradually settled down as the engine bounced up and down on its mounts. Crude or what! Engine note and speed decreased at point of lockup.

        I blame those buses, their braying, outlandishly noisy two-stroke GM diesels and the pathetic transmission for ruining the quiet of our city at night when introduced. Went to London for grad work in 1969, and it was obvious that a AEC 4 stroke diesel packing all of 120 hp and four speed preselector gearbox not only got a double-decker bus going from stop much quicker than a GM bus, it was at least 10 times quieter doing it.

        Speaking from my point-of-view as a mechanical engineer. In those days as a student I had to ride buses and had a keen interest as to why the GM was so unrefined and the engine so noisy. No domestic competition would be my guess.

        1. Noisy or not, I loved those old roaring GM buses, when in “hydraulic drive” mode. That mode would seem to be not very fuel-efficient; a 4-speed pre-selector as you mention, should indeed have been more fuel-efficient (as well as quicker, as you mention). I have read that a later version of this Allison transmission arrangement actually had a second gear, making for a true two-speed, plus lockup in high. I cannot confirm that, though.

  21. I’ve heard a story about the Hydra-Matic, as follows:

    Supposedly Rolls-Royce acquired a Hydra-Matic for evaluation. They liked it but thought one particular part had too rough a finish. When they fabricated a smoother-finished version of the part and incorporated it into the reassembled Hydra-Matic, the transmission didn’t work. True, or urban legend?

    1. I’ve heard that story in regard to the Turbo Hydramatic (not the original), which Rolls-Royce also built. The way I’ve heard it is more that they tightened up the tolerances, which didn’t necessarily work out well. I don’t know if it’s true or not, but it’s not implausible. There’s an analogy to be made with pistols, where getting everything “tuned” to tight tolerances improves accuracy, but makes the action less tolerant of dirt or debris. (This is why police and military sidearms are not built like target pistols.)

      1. I am reasonably certain that while Rolls Royce licensed & built in England the original HydraMatic, it imported the Turbo HydraMatic 400 from GM in the states.

        1. You’re correct; my previous comment was based on a point I was only half-remembering. They did import them, but asked for higher-than-standard tolerances.

  22. Thank you for this very complete summary. I have been curious about these transmissions for quite some time, and this is quite helpful. Your research is impressive, as is the writing.

  23. The main problem with reliability of the Slim Jim was the weakness of the front oil pump cover; they cracked. An improved pump with webbing on the cover was designed to replace failed units. RHM 375 Model 10’s made at Willow Run ceased in 1962. The THM 350 signalled the beginning of a long slide toward mediocrity by GM.

    1. I have to wonder if the Roto Hydra-Matic’s various weaknesses, including the propensity for leaks and the issue you describe, were exacerbated by the very high operating pressures. As mentioned, the RHM’s operating pressures were substantially higher than the earlier dual-coupling HM’s, which is a lot of added stress to put on what was still fundamentally an adaptation of the earlier transmission.

      I’m not sure how your last statement follows. The THM350, which didn’t arrive until five years or so after the RHM expired, was effectively a replacement for the Powerglide and Super Turbine two-speed automatics, and in that sense were an improvement in most respects. (There have been some harsh criticisms of the later TH200, but that’s a different story.) Since most rivals had long since offered three-speed automatics for most engines, the TH350 was also arguably overdue. It wasn’t quite as heavy-duty as the TH400, but it wasn’t designed to be, trading off some torque capacity for lighter internals and lower power consumption.

    2. I would disagree; I had very good luck with the THM350 in my 1973 Nova 350; it reached 185,000 miles, with no issues other than some fluid leakage. Shifting was still quick and firm. I have not heard of a lot of issues with this tranny.

      1. The lighter TH200 has gotten a pretty bad rep, but I’ve never heard anything particularly bad about the TH350.

  24. I had a 1949 buick super with dynaflow, four door. It averaged about 8 mpg. It took everything I earned as a super market clerk to keep the transmission running, most repairs were $300 to $400.

  25. Studebaker developed their own automatic and introduced it in 1950. Ford wanted to license it, but Studebaker turned them down. Studebaker started using the Borg Warner later, when manufacturing costs of theirs got too expensive. If I recall, a European manufacturer bought the tooling, and used it in their own cars?

    1. I believe the Studebaker automatic became the basis of the Borg-Warner DG, which was used on a number of British and European cars of the ’50s.

  26. Thanks so much for the great overview.

  27. Great job like the article ? would you have any info on the olds roto hydromatic . I have a 62 any m having some small issues
    Thank you Mike

    1. I’m not able to help with any kind of troubleshooting or repairs, sorry!

  28. Thanks again for a great resource. I find myself returning to it for a periodic refresher when a relevant vehicle appears. (Today’s is a 1961 Buick.)

    1. Thanks, Ed! I’m actually in the process of updating this article as I recently did with the Hydra-Matic story, to fix some minor factual glitches, clarify the technical details (which is a major project, let me tell you), and add some new info.

  29. All this effort and expense just so drivers don’t have to clutch and shift? Turns out major beneficiaries of automatic transmissions are texters. Who cause many of the accidents on the road now!

    1. Given the timeframes of the respective inventions, I would said that definitely constitutes an unanticipated side benefit…

  30. I believe that the first automotive use of planetary gears was in the Model T. As I recall, you would press down on one pedal to get the car going (1st gear), then move the gear lever and let the pedal up for high gear. It wouldn’t have taken much to use a servo to make these motions and a combination speed and throttle position sensor to determine when to make them. That could have been an early two speed automatic. The original Hydra-Matic is just a more sophisticated, four-speed version with a fluid coupling, isn’t it?

    1. That is how a Model T transmission worked, although it was not the first automotive application for epicyclic transmissions; a number of other cars, including Cadillac, used planetary gears before the Model T was introduced. (I’m always leery of pointing to anything as The First just because it’s often wrong unless you add a lot of qualifiers — a surprising number of innovations were tried or at least considered decades earlier than you might expect, even if manufacturing or machining technology wasn’t up to making it work.)

      It is certainly true that Henry Ford remained a stubborn proponent of planetary gears, which he continued developing for tractor use even after he was persuaded to allow a conventional gearbox in the Model A. (One of the engineers who worked closely with him in that, Howard Simpson, went on to design and patent the “Simpson gearset,” licensed by many other manufacturers including GM and Mercedes-Benz.) However, the Model T certainly wasn’t automatic and it would have needed some other control mechanism to execute shifts without driver intervention.

      As Part 1 of the Hydra-Matic article touches on, there were various efforts to do that, many of which used planetary gears because the brakes and clutches could be controlled hydraulically, electromagnetically, or by some other remote mechanism. So, there is a parallel, but it only goes so far and there were a lot of steps in between.

  31. Minor glitches: The TH 400 was used by Buick AND CADILLAC in 1964. The variable-pitch stator was not used on the TH 400 in ’64, but was available on some Olds, Buick, and I guess Cadillac vehicles from ’65–’67. Ironically, the variable-stator design was used on the “big” engines in the more-expensive cars; the small-blocks and six-poppers needed the torque boost more than the big-blocks.

    For the record, the ’64 TH 400 uses a substantially-different valve body and in-case fluid channels than the ’65-newer TH 400. The valve body of the front-wheel-drive version (the TH 425) uses the ’64-style system. Therefore, a “shift kit” for a 65-newer TH 400 won’t fit a ’64 TH 400 or the TH 425, but a shift kit for a TH 425 will work in a ’64 TH 400.

    The TH 350 was actually a joint development of Chevrolet and Buick engineers, both divisions looking for replacement of the two-speed transmissions they were currently using (Powerglide and Super-Turbine 300) with the resulting “350” produced by the Hydra-Matic Division.

    1. Thanks for the notes — I’m aware of both of the errors you note and they’ll be fixed in the extensive revamp of this article on which I’m currently working. (See the most recent post for details.) I won’t be getting into a detailed discussion of Turbo Hydra-Matic in the revised version, which is already monstrously long and has been eating my brain for months.

      TH400 wasn’t offered on all 1964 Cadillacs, incidentally; it was initially available only on De Ville, Eldorado, and Fleetwood Series Sixty. I wasn’t aware that the TH425 used the original valve body pattern, though. (I know generally how the TH425 is laid out, but I can’t say I’ve ever looked at its hydraulic control layout.)

      1. Okay, the revision is now complete and those corrections are now reflected in the text.

  32. Great, great job Aaron! That was awesome, and I was glad to help

  33. I think I can appreciate how big an undertaking revising this article has been. Hats off to you Aaron, for possibly the best explanation of early GM automatics expressed in laymans terms.
    GM didn’t swallow its pride and licence the Simpson system and tried to develop practical cost effective alternatives in its various divisions until the ’60s. Seems a classic case of corporate wilful blindness until we remember hindsight is the only exact science.
    In 1966 “Motoring Which?” the UK’s equivalent to “Consumer Reports” published a test of three 1.5 liter automatic British sedans, a Ford, a Hillman, and a Vauxhall. Vauxhall is the UK subsidiary of GM. The Vauxhall had a GM two speed transmission, the others both used a Borg Warner 35 three speed. They noted that they all had slightly worse performance and fuel economy than their stick versions, but the Vauxhall also had a big gap in its performance between 35-50 mph just when it was most needed. It was likened to driving a stick four speed using only second and top gears. The article also mentioned “Consumer Reports” had harsh words for GM cars using two speed transmissions, I’m guessing Ford, Chrysler, and AMC had all switched to three speed transmissions by then?.

    1. By 1966, I think Ford’s two-speed Fordomatic may still have been available for the cheapest U.S. Falcon models — I would have to double-check, as it may have been dropped after 1965 — but otherwise the other U.S. automakers all had smaller three-speed units for their low-end cars by then. (The light-duty TorqueFlite was one of the big pluses of Chrysler’s compact Plymouth Valiant and Dodge Dart, in my view.)

      The general attitude of GM engineers in this era was that a two-speed torque converter automatic was a perfectly reasonable substitute for a three-speed manual transmission while being simpler, lighter, and cheaper than a three- or four-speed automatic. The latter was of course perfectly true and the former was at least a supportable position. I also suspect some of the transmission engineers were soured a bit by experience with the small three-speed Hydra-Matic, which was little better than a decent two-speed automatic. (The transition from the smaller three-speed unit in the 1961–1963 Y-body Oldsmobile F-85 to the two-speed Super Turbine 300/Jetaway in the 1964+ A-body equivalent was certainly no great loss and probably an improvement in some respects.) On the other hand, by the mid-sixties, very, very few Americans still bought three-speed manual transmissions and it was certainly clear that a good three-speed torque converter automatic was considerably better than the best two-speed. It was also a bigger deal for non-U.S. cars and the later U.S. ventures into the “subcompact” [sic] realm, since having 3 or more liters’ displacement to fall back on masks an assortment of deficiencies.

      I don’t think GM was willfully blind so much as having a fair bit of (understandable) inertia. As this article should hopefully make very clear, GM had invested an absolutely staggering amount of money in automatic transmission development and engineering, accumulating a towering stack of basic patents. The tooling alone was a king’s ransom — in the early fifties, Detroit Transmission built more Hydra-Matics each year than the entire contemporary British auto industry built cars, and that wasn’t even GM’s only automatic! So, a reluctance to completely reinvent the wheel or to unnecessarily license outside technology isn’t difficult to understand. (To be clear, what GM licensed from Simpson and Simpson’s estate was a specific arrangement of planetary gears, not a complete transmission. Part of the reason that arrangement ended up being so widely licensed was that Simpson, like Pol Ravigneaux a decade or so before, had patented many different variations that there was no getting around them.)

      1. I’d forgotten three speed manual transmissions were still commonplace in the USA in the timeframe we are discussing. A two speed automatic makes a lot more sense then.
        I wasn’t suggesting GM was willfully blind, but had missed a trick in not adopting the Wilson system (or at least parts of it).
        As you say, GM spent vast amounts developing their transmissions. I wonder how much it cost Chrysler Corp to licence and develop their transmissions, which I think were superior to any other automatic transmission available at the time.

        1. To be clear, what’s commonly called a “Simpson gearset” really just refers to any compound planetary unit sharing a single sun gear, just as a Ravigneaux gearset is a compound planetary unit sharing a planet carrier and at least one planet gear. There were actually multiple variations of each, most of which Howard Simpson and Pol Ravigneaux dutifully also patented. While each of those layouts has certain advantages, particularly as regards packaging and cost, the invention, as was, didn’t encompass how the gears were selected and chosen. In fact, while there were a bunch of automatic transmissions that used these gear layouts, including Chrysler’s TorqueFlite and GM’s Turbo Hydra-Matic, each was quite a bit different. So, the credit for the functional effectiveness of TorqueFlite or Turbo Hydra-Matic really goes to the Chrysler and GM engineers who developed them. I’ve never seen anything to suggest how much any of the companies paid to license Simpson’s gearset patents, although there were so many users that if there was any kind of per-transmission royalty, Simpson and his estate would have made out quite handsomely.

          Developing an automatic transmission was a very costly business in general, I have no doubt, but in Chrysler’s case, they developed fewer of them — the original PowerFlite two-speed torque converter automatic, the early iron case TorqueFlite, and then lighter aluminum TorqueFlite units with a variety of evolutionary changes — and used them across all the automotive models. GM, by contrast, had three distinct transmission families (Hydra-Matic, Dynaflow, and Powerglide) that each went through several generations and iterations, each notably different, but with a lot of what a software designer might call legacy features. (The outliers there were Turboglide and Flight Pitch Dynaflow, which were not “clean-sheet” designs in a conceptual sense, but shared little with Powerglide and earlier Dynaflow transmissions mechanically and later contributed various ideas and some components to subsequent versions.)

          The three-speed manual transmission occupied a very peculiar space in the American automotive firmament in the sixties and seventies, being simultaneously ubiquitous and rather uncommon. It was notionally standard on a great many cars into the late seventies, but you’d hardly ever see one. The real rationale for its existence, so far as I can tell, was to allow a greater retail markup on the automatic transmissions (or four-speed manual transmissions) most people actually bought. By this point, no one pretended that Cadillac or Imperial buyers would have a manual gearbox, even the carriage-trade versions, but the three-speed was still nominally standard equipment on some quite improbable big sedans.

  34. Great job Aaron, you’ve outdone yourself. I enjoy coming to this site to expand my knowledge. It’s a fantastic resource indeed. I also enjoy your clarifications on “Curb Side Classics” and can faithfully know that any input you offer will be well reasoned and researched. You offer a great service to like minded Auto Industry nuts.

  35. Wow! My brain has tech-overload.I’m going to have to re-read the article in sections to have any hope of absorbing all the new information. Fantastic job on the revision, Aaron, it was well worth the wait. Thanks for the monumental effort!

  36. Great article! One point of contention is some of the THM-400 transmissions fitted to Chevrolets did have the “switch-the-pitch” feature I remember working on a 67 Impala station wagon, with the 327″ engine and THM 400 which had the pitch angle switch on the throttle linkage. This was in the early 1970’s and this appeared to be an O.E. Installation on a stock automobile.

    1. Hmm. To be honest, I had thought until this afternoon that TH400 wasn’t offered with the 327 at all — a number of vintage car magazines complained about that, in fact — but I found one brochure that indicated the 327/THM combination was indeed optional on the ’67 Impala and Caprice. (It may have been a midyear or late introduction.) I’ve never seen any indication that the TH400 fitted to the big Turbo-Jet engines (396/427) had the variable-pitch stator, but it’s possible the ones used with the 327 did. If so, it was likely short-lived, as the switch-pitch stator was dropped for 1968. However, a 327 with switch-pitch THM actually sounds like a pretty nice combination. It would be much more flexible than Powerglide, that’s for sure!

      (I tried very hard not to get sucked into a more involved discussion of Turbo Hydra-Matic in this article for what I imagine will be obvious reasons, but I wanted to mention the variable-pitch stator because it was really one of the only Dynaflow/Twin Turbine/Turbine Drive features to survive into the later era.)

  37. I was under the impression that Chevrolet division never used the variable-pitch stator design, but regarding the 327/THM combo for big Chevrolets – it seems likely. Olds offered the THM 400 as an option on it’s small-block (330/350) powered 88 models for sure in ’67 & ’68, not positive about ’65-66. Both my ’67 Delmont 88 330 and my ’68 Delmont 88 350 came with THM400’s rather than the usual Jetaway 2-speed (ST300). The ’67 is a variable-pitch model, the ’68 is fixed. In normal operation, I don’t really see a pronounced performance advantage to the variable-pitch stator.

    1. The other divisions’ experience isn’t necessarily suggestive regarding TH400 availability. Buick, for example, offered it on the smaller-engine LeSabre (with the 300 cu. in. engine) as early as 1964, whereas the loosely comparable Oldsmobile Jetstar 88 was available only with the two-speed in ’64 and you could still get Jetaway on a base-engine Delta 88 until 1969. Chevrolet didn’t offer Turbo Hydra-Matic at all until mid-1965 and until 1967, it was only available on full-size cars with the 396 or 427. I think part of the rationale was that TH400 was bulkier and consumed more power than Powerglide (hence the later TH350), although the 327 obviously could have benefited from an extra gear.

      When Oldsmobile dropped the variable-pitch stator for 1968, they also gave both Jetaway and TH400 higher-ratio torque converters, so there really isn’t much difference in all-out performance. The point of the variable-pitch stator vanes was to keep the converter “tight” in gentle driving while still providing extra multiplication for fast starts or quick bursts of acceleration, even if you were over the maximum kickdown speed. With the kind used on Turbo Hydra-Matic and Jetaway/Super Turbine 300, it also limited creep on a closed throttle. (The old Buick and Turboglide stators variable couldn’t do that because the stator servo valve was triggered by throttle movement rather than electrically.) So, it was about flexibility more than anything else.

  38. Terrific article with this latest revision!

    The first car I can remember was a ’56 Oldsmobile and by the time I was 8 years old or so my dad had described to me how the “fill and flush” coupling worked in cushioning the shifts. Anytime we were driving I kept track of which was in use. Walking to school I would hum to myself as I walked, imitating the engine speed ramping up in each gear, pretending to be a car with Hydramatic.
    The Oldsmobile was replaced by a Buick LeSabre. We ended up buying the “400” version in order to avoid the two speed automatic. The “switch the pitch” stator was what got Dad’s attention in this car (even if its actual operation wasn’t very noticeable).
    Stuff like this is what motivated me to become a mechanical engineer.

    Thanks for all of your work. It brings back good memories.

    1. Thanks, Chris. I can see that the Controlled Coupling Hydra-Matic would be sort of a crash course in mechanical engineering, since it has a little of just about everything. Bands! Couplings! All kinds of clutches — disc, multi-disc, cone, and sprag! If it had a torque converter and a lockup clutch, it would be a veritable omnibus of early automatic transmission ideas. (If they’d used Walter Herndon’s lockup clutch concept, it wouldn’t have been a complete lockup in the sense of a modern torque converter; it would just have locked out the smaller coupling.)

      What I love — and GM accountants presumably did not love — about the second-generation Hydra-Matic is that it incorporated a bunch of changes that make its basic operation smoother and mechanically simpler, but each change then required a bunch of belts-and-braces stuff to make up for the minor drawbacks created by the simplification, such the need to still use separate overrun brakes so as to not end up freewheeling down every steep hill. It’s a useful reminder that just because something is cleverer doesn’t necessarily mean it’s better.

    2. And here I thought I was the only kid (early ’50s) to imitate a Hydramatic!

  39. Great information.
    Drawing on personal experiences from cars my friends and I owned when we were young men two speed automatics, mostly powerglides, were something we wanted to get rid of if we could afford it. I had a ’65 Pontiac Laurentian (283-2 speed) ’64 Chev Impala SS (283-2 speed) and a “68 Camaro ( 327-2 speed).
    I put a Turbo 350 in the Camaro later and it was a nice addition.
    I know the racecar guys like them but we had full size ’60’s sedans with 283’s and 235’s, not 800-2000 horsepower racecars.
    To this day ( I’m 60) I would rather have a manual than automatic transmision I think because of powerglides.
    In the late ’80’s I learned about Variable Pitch converters some Turbo 400s had, bought the pieces from Kenne-Bell, converted my ’80 GMC ( 350, later 454) heavy half and ’74 Olds (455) Delta 88 convertible over to them. I also added the 2.75 low first gear kit to the Olds also because I’m married to the 2.73 rear gears ( 9 3/8 ring gear diamter) so I’m looking for mutiplication wherever I can get it.
    With the warmer than stock cam (268 Comp Cams) It gives me way better traffic drivability than I had before, particularly when towing a trailer on holidays.
    According to a book I once had, it claimed the fixed pitch 400 converter stator angle is 24 degrees if my memory serves me correctly. I think the Variable Pitch swings between around 18-26 degrees. I have to get another book to be more accurate. I have a variable pitch stator and if you put it through its motions you can see how it would give different stall angles, all you have to do is compare it to boat or aircraft propellers.
    According to my information a fixed pitch 400 converter gives up to 2:00-1 multiplication and variable pitch goes up to 2.5:-1. That helps in a heavy car with tall rear gears.
    Over the years i’ve been to a few “burger stand or shopping mall car shows” and described the variable pitch converter system the guy has on his car and he generally has no idea what i’m talking about.
    Some years of Oldsmobiles (the ones I’m most familiar with) had a switch in the speedometer cable and was in high pitch until a certain speed and some had it in their throttle linkage.
    If one is not careful when they have their transmission rebuilt the variable pitch stuff is not put back in and fixed pitch stuff substituted.
    Transmission repairmen, if not familiar with it tend to think it’s an earlier fluid coupling and primitive garbage from the days before “real” transmissions were made. They”re usually pushing a modified TH700R4 which, in my humble opinion, is not designed for a big motor in a heavy vehicle.
    That being said, the decendant, the 4L60E, is doing just fine in my stock ’96 Impala SS and that 700 would have been a huge improvement in our old ’60’s cars.
    However, some know exactly what that VP is, and if the owner has no idea what he has and someone they know wants one, it’s gone.
    This happens to the factory low first gear kits that are in motorhomes and heavier trucks too.
    The variable pitch really shines when you run more cam or a turbocharger, in high stall they let the engine get above 2500 rpm before they stall and let the engine wind up, making more power.
    In high stall it’s too high to have all the time and in low stall it would leave you wanting more in stop and go traffic, particularly when towing something, but together a nice blend.
    They, along with 2.75 or 3.00:-1 low first gear and overdrive kits were the darlings of the motorhome crowd until heavy versions on the overdrive automatics came along. Those in the know had them, guess where some of them pieces came from. Not everyone in this world has scruples.
    GM made two sizes, the mid size “A bodies” had 10 inch and full size sedans had 12 1/2 inch.
    The big fixed and variable pitch torque converters were the same size and the stators interchanged but the varibable pitch ones were referred to as 12 1/2 inch and the fixed pitch ones as 13 inch.
    I was told the reason was that’s how GM differentiated between the two.
    Several things that I have read over the years described the phasing out of the variable pitch according to GM was it was “a feature that only engineering types seemed to understand plus some customers complained about the whirring noise they made”. And,” with the new large displacement engines coming out it is unecessary”.
    Why spend money on a feature something very few people understand?
    With an overdrive kit, and a variable pitch a TH400 becomes a 12 speed. Not a cheap proposition though.
    Thank you and enjoy.

    1. Thanks for your thoughts, Wayne. The pitch angles of the TH400 variable-pitch stator were 32° and 51°, at least as GM measured them. Fixed-pitch TH400 converters actually varied quite a bit in stall ratio depending on the application, from 2.00 to about 2.50:1 for street applications, whereas the standard variable-pitch units were 1.8/2.2. The switch-pitch stator didn’t necessarily mean greater maximum multiplication. As you note, the main advantage is that you have the higher stall speed when you need it and aren’t stuck with high-stall converter blues the rest of the time.

  40. A monumental amount of work involved in this revision. A labor of love really. Congratulations on unraveling the details in all these GM transmissions, and presenting the results so clearly.

    My further kudos in your even responses to comments where old wives’ tales and “my friend the transmission overhauler tells me you’re wrong” comments seem intent to belittle you. Haven’t seen anyone conclusively prove you incorrect, possibly because you know about 10 times more than they do, and I’m speaking as a retired mechanical engineer who’s had people who just don’t understand that they don’t understand try to sell me a line of magic dreamed up in their heads! It’s how myths and legends are born. AWD systems seem to be completely misunderstood by just about everyone but the engineers who designed them, for example. Especially that particular group of people known as Marketing and their adjunct advertising copywriters.

    If one goes back a bit further to the brief time interval between synchromesh and the first Hydramatic, my speculation for the real reason an automatic transmission was needed was because so little effort was ever applied to designing a half-decent shift linkage and low clutch effort. That’s why people hated driving those clunkers – they were awkward to say the least. Try a ’49 Pontiac three-on-the-tree. Blech.

    So when we youngsters got to drive Austins and euro Fords in the 1950s and heaven! the first Volvo 4 speed manual, the ease of use was outstanding compared to the US stuff. No longer was shifting a chore, it was fun, column or floor shifter. I mean Chev thought the Powerglide more important to introduce than replacing the oil dippers on their six cylinder engine and giving it proper full pressure lubrication, so designing an ergonomic manual shifter was obviously beyond them. Strange attitude to me other than dreams of golden showers of dollars raining upon them for presenting no-shift motoring at a premium.

    Even early to mid ’60s 4 speeders needed a manly-man to shift their obdurate levers. No snickety-snick there. The Corvair 4 speed was an outright laugh compared to the Volvo, but in those days the scorn heaped on “tiny” foreign cars meant Americans in general somehow believed that foreign ideas came from the dark ages and were no good. Same in Canada where I live and lived through endless Ford versus Chev arguments in both high school and college where nothing was ever settled.

    All that personal reflection aside, I must reiterate you’ve put forward a first class effort here and deserve much praise. It’ll probably become a reference work.

    1. Thanks, Bill. It’s certainly true that the shift linkages of domestic cars had a lot to do with the preference for automatic. Three-on-the-tree is mildly amusing to the modern driver as a novelty, but a regular dose of it — particularly with a non-synchronized (or indifferently synchronized) transmission — would be a strong argument for Powerglide. As for the sixties four-speeds, I assume part of the problem was that they were intended primarily for racing homologation or drag racing, rather than something your average consumer might buy (a thesis strongly supported by the fact that a four-speed typically cost as much as or more than automatic).

      On the other hand, there’s a strong argument to be made that automatic transmission is a natural evolutionary development of automotive technology, just like, say, automatic spark advance (another development that was still fairly recent when Hydra-Matic first came on the scene). Even with excellent modern five- and six-speed gearboxes, effective synchros, and low-effort clutches, it’s hard for me to argue that manual shifting is a lot of work of a kind many drivers are perfectly happy not bothering with. The strongest arguments for it, aside from it being a moderately entertaining diversion, are that it makes the most out of smaller engines without a lot of torque and that it spares you the exasperation of delegating a complicated chore to an automated subordinate of often questionable judgment, both of which have become progressively weaker as engine and transmission technology improve. (I say this, mind, as someone who has never owned a car with automatic transmission and who had to learn to drive on a manual gearbox.) So, I can understand, though not really defend, why Detroit engineers treated manual transmissions as a legacy system only being (grudgingly) retained for buyers too cheap to pony up the extra $200-ish.

      (What’s harder to understand, frankly, is that GM let O.K. Kelley and his guys keep churning out different automatic transmission designs of several very different flavors for an astonishingly long time before they finally decided to consolidate around yet another, mostly unrelated design!)

  41. I WANT TO INSTALL EXTERNAL AIR COOLING COILS TO A BUICK DUAL PATH TRANSMISSION
    (1961 to 1963). I cannot find any information on this. I need to know if it can be done and if so what ports on the transmission do I use?

    1. I’m afraid I’m not qualified to advise you on modifying your transmission, especially not in the way you describe. Sorry!

  42. One problem with the original Hydramatic transmissions made prior to the Dual-range Hydramatics, which came out in 1952, is how drivers were able to get engine braking when there was no way to downshift a hydramatic car from fourth to third gears. So if you going down a long, steep hill at about 55 mph there was no way to get engine braking with the original Hydramatic. My father had a 1954 Buick with Dynaflow and you could manually downshift from High to Low at 55 mph or slower and get engine braking going down a hill. The Dynaflow was a super smooth transmission and with torque converter technology I think was a very underrated transmission compared to the Hydramatic. It was also very reliable and we had the 54 Buick for 13 years with no problems with the Dynaflow.

    1. Dynaflow versus Hydra-Matic was really a fascinating philosophical debate, especially when you consider that they were conceived by many of the same people. Hydra-Matic was efficient and, at least in Dual-Range and later forms, versatile, but it was also complicated and fussy. Dynaflow was seamless, but, especially with the earlier ones, you really had to use Low a lot to get the best out of it. It’s very interesting to me that GM spent so much developing these two wildly different transmission concepts.

  43. hello i am changing cooler on my dads 58 olds holiday hydra-matic jetaway “slimjim” and would like to know what size threads are in cooler boss on tranny

    1. Derik,

      As I keep saying, I am not able to advise people on repairs, modifications, or restoration — you will need to find a shop manual for that information. The good news is that you may be able to find one online (try the Old Car Manual Project) or at your local public library.

      To avoid confusion, I will note that the 1958 Oldsmobile Hydra-Matic is NOT the transmission popularly known as “Slim Jim,” but the earlier and considerably bulkier dual-coupling four-speed unit, also known as the Controlled Coupling Hydra-Matic.

  44. Hello Mr Severson, could you tell me more about the engineer Gilbert Kenneth Hause? Thank you so much.

    1. I’m afraid I have no biographical information on him other than that he was part of Kelley’s corporate Engineering Staff transmission group in the late ’50s and was involved in the development of the triple turbine automatics and Dual-Path Turbine Drive, as well as some variations of those transmissions that never made it to production.

      1. Thank you for your response. Unfortunately, I’ve also asked to the GM Heritage center and I didn’t obtain more informations.

        1. What you might try is doing a patent search on his name. While that won’t provide you with much in the way of biographical detail, patent disclosures include the inventor’s city and state of residence at the time of filing. Reviewing an engineer or inventor’s patent history can sometimes give you a decent idea of their career progression. For instance, if Hause left GM to work for another company, the assignee data for subsequent patent filings might tell you where he went and provide a general timeframe.

          1. Thanks for your advise! In particular, I wanted to know the early years of his career. Apparently, he worked to GM in late thirties. He was specialized in the engineering relative to the hydraulic systems including the disk brakes, pumps and and indeed the transmissions.

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