It can be identified by "375-THM" cast into the tailhousing. All THM400 units had a 32 spline output shaft with the exception of the THM375 that used a 27 spline output.Ī Hydra-Matic 3L80 transmission, produced between 19, at the Ypsilanti Automotive Heritage MuseumĪ variant of the THM400 known as a THM375 is a THM400 with a mid length 27 spline output shaft that mates to the smaller THM350 27 spline drive shaft yoke. Other units to include the 2 prong connectors had an internal pressure switch that was used to control spark timing retard. The switch pitch is not the only THM400 that utilizes an external 2 prong connector. This transmission (among other THMs) is identified by the "Park R N D L2 L1" selector quadrant. GM used a Switch Pitch torque converter in the Buick twin turbine Dynaflow transmission between 1955–1963 and the Super Turbine 300 two speed transmissions used by Oldsmobile, Pontiac (Pontiac's ST300 didn't have a switch pitch), and Buick divisions between 19. Externally the switch pitch version has two electrical connections, where the non-switch pitch THM400 has only one. These can be identified outside the vehicle (with the torque converter removed) by a narrow front pump spline. Many of the Buick, Cadillac, and Oldsmobile THM400s produced between 19 were equipped with a "Switch-Pitch" torque converter with a variable-pitch stator, which is sought after by collectors and drag racers. The following year, application expanded to Oldsmobile and Pontiac and to some full-sized Chevrolets. First introduced for the 1964 model year under the name "Turbo Hydra-Matic" in Cadillacs and "Super Turbine" in Buicks. The THM400 can be visually identified by an oil pan number four shown at General Motors Transmission Pans. Super Turbine 400 / THM400 / THM375 / 3L80 / 3L80HD Turbo-Hydramatic 400 Transmission Starting in the early 1980s, the Turbo-Hydramatic was gradually supplanted by four-speed automatics, some of which continue to use the "Hydramatic" trade name.Īlthough the Turbo Hydra-Matic name alludes to the original Hydra-Matic developed by General Motors' Cadillac division in the late 1930s, the two transmissions were not mechanically related. By 1973, THM units had replaced all of GM's other automatic transmissions including Chevrolet's Powerglide, Buick's Super Turbine 300, and Oldsmobile's Jetaway. The Buick version, which followed shortly thereafter, was known as the Super-Turbine 400. In its original incarnation as the Turbo-Hydramatic 400, it was first used in the 1964 model year in Cadillacs.
#Gm turbo 350 transmission diagram series#
The Turbo-Hydramatic or Turbo Hydra-Matic (THM) series was developed to replace both the original Hydra-Matic models and the Buick Dynaflow.
#Gm turbo 350 transmission diagram plus#
These transmissions mate a three-element turbine torque converter to a Simpson planetary geartrain, providing three forward speeds plus reverse. Turbo-Hydramatic or Turbo Hydra-Matic is the registered tradename for a family of automatic transmissions developed and produced by General Motors. 3-speed longitudinal automatic transmission
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