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The Turbo-Hydramatic or Turbo Hydra-Matic (THM) series was developed to replace both the original Hydra-Matic models and the Buick Dynaflow. In its original incarnation as the Turbo-Hydramatic 400, it was first used in the 1964 model year in Cadillacs. The Buick version, which followed shortly thereafter, was known as the Super-Turbine 400.
Introduced in 1964, Turbo-Hydramatic use quickly spread across all GM divisions, and they became referred to simply as Hydramatics (like GM's original automatic of totally different design), except for the Super Turbine 400 model. By the 1970s, Turbo-Hydramatic variants had replaced all of GM's early automatic transmission designs. In Argentina ...
It was the 4-speed electronically commanded evolution of the 3-speed Turbo-Hydramatic 400, first produced in October 1963. 4L80-Es were optioned only in Chevrolet/GMC pickups, vans, and commercial vehicles, and the Hummer H1.
The TH400 was phased out for the 1980 models, when the A-727 replaced the TH-400 as the only automatic transmission option for both the SJ Wagoneer/Cherokee wagons and the J-10/J-20 trucks. Internally similar to the Chrysler A-727, the case was one-piece, cast with an AMC pattern bellhousing (not interchangeable with a Chrysler pattern A-727).
Cast-iron Hydra-Matic production ceased at Willow Run after the 1962 model year, and Controlled-Coupling Hydramatic ceased in early 1964, allowing retooling time for the Turbo Hydra-Matic 400, which debuted in the 1964 Cadillac models in mid-year, with Pontiac Division's Star Chief and Bonneville models being the last to use the Controlled ...
One feature of the Dynaflow, the variable-pitch torque converter stator, colloquially the "Switch-Pitch", lived on in versions of the Turbo-Hydramatic (Super Turbine 400) fitted to full-size Buicks, full-size Oldsmobiles and Cadillacs built from 1965 to 1967, as well as the Buick Super Turbine 300 and Oldsmobile Jetaway from 1964 to 1967.
The THM-400 is torque converter based, similar in design to the Chrysler Torqueflite and Ford Cruise-O-Matic transmissions. Despite the Turbo Hydramatic 400 still bearing the "Hydramatic" name, it shared no design components with either of the older fluid-coupling based Roto or Super-Hydramatics.
In 1969, the three-speed Turbo Hydramatic 350 (THM350) was introduced as a light-duty companion to the Turbo-Hydramatic 400, and made available on virtually all Chevrolet cars and trucks with six-cylinder or small and medium-sized V8 engines, as well as intermediate sized cars of other GM divisions. [2]