Early models
The General Motors Automatic Safety Transmission (AST) was a semi-automatic transmission released in 1937. The first mass-produced fully-automatic transmission developed for passenger automobile use was the GM Hydra-Matic introduced in the autumn of 1939 as a (very likely subsidized) $57 option for the 1940 Oldsmobile. [1] The Hydra-Matic was then offered by Cadillac starting with its 1941 models, and by Pontiac for 1948. It enjoyed wide success. Also for 1948, Buick introduced its Dynaflow automatic transmission, and for 1950, Chevrolet offered the Powerglide automatic. This meant that, by 1950, GM marques offered three automatic transmissions at a time when most of its competitors still offered none.
Throughout the 1950s, all GM Marques continued developing automatic transmission designs, both jointly and independently. Early models included:
- 1937–1939 GM Automatic Safety Transmission (AST) — Offered by Oldsmobile for 1938-1939, and by Buick in 1938 only. This was a semi-automatic transmission that required the driver to use a clutch to get the car moving, but once underway, the AST shifted itself. The clutch was only needed if the driver needed to use the gear selector lever, for example, to shift into reverse.
- 1940–1967 GM Hydra-Matic — The first automotive automatic transmission, a 4-speed unit, introduced for 1940 by Oldsmobile, and ultimately also offered by Pontiac and Cadillac. Except for its name, it bore no relation to the later GM Turbo Hydramatic, 3-speed automatic transmission that was introduced in 1964.
- 1947–1952 Buick Dynaflow — The first Buick automatic transmission, a 2-speed unit, introduced for 1948. It was designed for smoothness and shifted without any perceptible gear changes, somewhat similar to modern continuously-variable transmissions. For this reason, vintage car enthusiasts today sometimes call it "Buick's 2-speed CVT."
- 1950–1973 Chevrolet Powerglide — The first Chevrolet automatic transmission, a 2-speed unit, introduced for 1950 and offered on both passenger cars as well as Chevrolet and GMC trucks. The Powerglide automatic transmission was also offered at different times by Pontiac, Holden, Vauxhall and Opel passenger cars.
- 1953-1955 Buick Twin-Turbine Dynaflow — For 1953, Buick introduced the 2-speed Twin-Turbine Dynaflow, a redesigned Dynaflow automatic transmission employing two turbines and a single stator for improved responsiveness and efficiency.
- 1956-1957 Buick Twin-Turbine 2 Dynaflow — For 1956, Buick offered the 2-speed Twin-Turbine 2 Dynaflow, a second redesign of the Dynaflow automatic transmission. The Twin-Turbine Dynaflow included turbines and a variable-pitch stator that changed pitch angle based on accelerator position for better responsiveness.
- 1956-1964 GM Dual-Coupling/Controlled-Coupling Hydra-Matic — For 1956, GM offered the first substantial redesign of the 4-speed Hydra-Matic automatic transmission. Along with numerous technical improvements, this new Hydra-Matic automatic transmission also included a Park position, something previous Hydra-Matic units did not offer (drivers locked the transmission by shifting into Reverse and turning the ignition switch off). This new Hydra-Matic was also called the Cadillac 315/P315 Hydra-Matic, the Oldsmobile Jetaway/StratoFlight, and the Pontiac Super Hydra-Matic.
- 1957-1961 Chevrolet Turboglide — For 1957, Chevrolet offered a new kind of automatic transmission that employed a constant-torque design that offered imperceptible shifts. The 3-speed Turboglide was not popular, as buyers thought it felt odd. It had poor reliability until a 1959 redesign (which helped, but came too late). The Turboglide was only offered on V8 models. The Corvette only offered the Powerglide automatic at this time.
- 1958-1959 Buick Flight Pitch Dynaflow/Triple Turbine — This was the third redesign of the Buick Dynaflow automatic transmission, a 3-speed automatic transmission that featured three turbines. It bore more than a passing resemblance to the Chevrolet Turboglide, even though Chevrolet and Buick worked separately on their transmission designs. It was called the "Flight Pitch Dynaflow" in 1958, and for 1959 it became the "Triple Turbine," as Buick moved away from the "Dynaflow" name. Beset with many teething pains, this transmission was only offered for 1958 and 1959.
- 1961-1963 Buick Dual-Path Turbine Drive. This 2-speed automatic transmission was used by Buick after it discontinued the Triple Turbine automatic.
- 1961-1964 GM Roto Hydramatic — A compact, 3-speed automatic transmission based on the GM Hydra-Matic. It was used at different times by Oldsmobile, Pontiac, Holden, Vauxhall and Opel on various models.
- 1962-1972 Pontiac TempestTorque — This was a 2-speed automatic transmission that was based on the Chevrolet Powerglide.
- 1964-1969 GM Super Turbine 300 — This 2-speed automatic transmission was a lower cost unit that was used on some Buick models as the "ST-300," some Oldsmobile models as the "Jetaway," and some Pontiac cars as simply the "Automatic."
- 1968-1971 Chevrolet Torque-Drive — Offered for a few years by Chevrolet, this was a two-speed semi-automatic transmission based on the Powerglide. There was no clutch, but drivers had to use the column-mounted shift lever to shift between low and high gears. Only available with 6-cylinder engines, the Torque-Drive didn't cost much less than the Powerglide, and did not sell well.
Turbo-Hydramatic 3-speed Automatics
Introduced in 1964, the GM Turbo-Hydramatic was an entirely new 3-speed automatic that featured a torque converter, as opposed to the standard fluid coupling that the original Hydra-Matic used. Buick, Cadillac, Oldsmobile, and Pontiac began offering the Turbo-Hydramatic fairly quickly after its introduction. By contrast, Chevrolet took much longer to replace the aging two speed Powerglide with the three speed Turbo-Hydramatic in its lineup, at first not offering the Turbo-Hydramatic at all, then only offering it on the most costly and powerful V8 engines on full size models, then finally offering it with all engines on full- and midsized models ... but not in the compact Nova. It finally took until 1973 before Chevrolet finally phased out the by then badly outdated Powerglide automatic transmission, long after the other GM divisions discontinued their old automatic units.
Across the GM divisions, the Turbo-Hydramatic was called simply the "Hydramatic," with a few exceptions, such as Buick's use of the term "Super Turbine 400." In Argentina, the Turbo Hydra-Matic was marketed as the "Chevromatic" in the 1970s. Starting in the early 1980s, the Turbo-Hydramatic was gradually supplanted by four-speed automatics, some of which continued to use the "Hydramatic" trade name.
Originally a medium-duty longitudinal rear-wheel drive design, other variants were later developed, including both light-duty and heavy-duty RWD versions, and both longitudinal and transverse front-wheel drive versions.
