|Class||3-speed transverse automatic transmission|
The Turbo-Hydramatic 125 was the first in a line of automatic transmissions from General Motors designed for transverse engine application. Introduced in 1980, the line evolved into today's 4T40/45/65/80 line.
This was a later model of the 125 that debuted for 1982, and included an ECU controlled solenoid that would engage the torque converter into "lock up" where engine power was transferred directly to the transaxle. The C comes from the use of a torque converter clutch (TCC). The solenoid that controls this is notorious for failure, their failure is indicated by an engine stall when braking from speeds greater than 55 MPH. This occurs because the clutch does not disengage and the engine cannot produce enough output to keep the vehicle in motion.
A breakdown of THM440T4 is: Turbo HydraMatic Model 440 - Transversely Mounted - 4 Speed Fully Automatic transmission
A 4-speed version of the 125 was created for the 1985/1986 GM C platform (FWD)/GM H platform (FWD) cars, the Turbo-Hydramatic 440-T4. Many parts were identical to the 125, though it was generally stronger and included an overdrive fourth gear. This transmission was first used in GM's 1985 Buick Park Avenue, Oldsmobile 98, and Cadillac Deville. In 1986, after switching to FWD, the Buick LeSabre, Oldsmobile Delta 88, and later, the Pontiac Bonneville also used this transmission. A special strengthened F-7 version was also used for the 1987–1992 Cadillac Allanté and 1989-1990 Pontiac Turbo Grand Prix.
One unique feature of this transmission is its use of both a modulator valve and a throttle valve (TV) cable. Most transmissions either use one or the other to control shift points and shift smoothness. On the Turbo 440-T4, the TV cable exclusively controls the shift points, while the modulator valve controls the shift feel. This feature makes it very easy for a home, "shadetree" mechanic to adjust the transmission shift points with minimum effect on the shift feel.
The 440-T4 was originally slated to be used with downsized C body cars for 1984, however, issues with failures led to introduction being delayed until 1984 for the 1985 model year.
The 440-T4 was later renamed the 4T60.
A heavy-duty version, the 4T60 HD was used for the 1989-1990 Pontiac Turbo Grand Prix.