TH400 History

The THM400 can be visually identified by an oil pan number four shown at Transmission Pans. It was first introduced for the 1964 model year under the name "Turbo Hydra-Matic" in Cadillacs.^[3] and "Super Turbine" in Buicks.^[4] The following year, application expanded to Oldsmobile and Pontiac and to some full-sized Chevrolets. Many of the Buick, Cadillac, and Oldsmobile THM400s produced between 1964-67 were equipped with a Switch-Pitch torque converter variable-pitch stator, which is sought after by collectors and drag racers. These can be identified outside the vehicle (with the torque converter removed) by a narrow front pump spline. Externally the switch pitch version has two electrical connections, where the non-switch pitch THM400 has only one. 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, and Buick divisions between 1964-1967.