GM Turbo-Hydramatic 425

Turbo-Hydramatic 425 was an automatic transmission developed and produced by General Motors. The THM425 was based on the design of the THM400, with most parts being identical and some others interchangeable with minor modifications. In the THM 425, the internal parts spin the opposite direction; for example, the helical angle of the planetary gears is "reversed" and the one-way clutches freewheel in the opposite direction. The THM425 was developed for the 1966 Oldsmobile Toronado and the 1967 Cadillac Eldorado. After the 1978 model year, both lines replaced the THM425 with a lighter-duty transmission known as the THM325. Starting in 1979, all longitudinal engine front-wheel drive vehicles used the THM325.