The TH400 transmission was GM's first design of automatic transmission in the Turbo-Hydramatic product line. It was first introduced in select 1964 models then rolled out completly the following year in 1965. Early 1964-1967 model Turbo 400 transmissions were equipped with a switch-pitch torque converters with variable-pitch stator. These model TH400s can be identified outside of the transmission, when the torque converter is off, by looking for a narrow front pump spline. Switch-pitch Turbo 400s also had two electrical connectors where the non-switch-pitch Turbo 400s only have one electrical connector.
GM had adpated the TH400 to be able to work with a large number of vehicles between its almost 30-year lifespan. The majority of internal components are interchangeable.