Turbo-Hydramatic 125

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Turbo-Hydramatic 125
Manufacturer General Motors
Production 1974–2002
Successor 4T40-E/4T45-E
4T65-E
4T80-E
Class 3-speed transverse automatic transmission
Related Turbo-Hydramatic

The Turbo-Hydramatic 125 was the first in a line of automatic transmissions from General Motors designed for transverse engine application. Introduced in 1974, the line evolved into today's 4T40/45/65/80 line.

Contents

[edit] Turbo-Hydramatic 125

The 3-speed Turbo-Hydramatic 125 was introduced in 1980 and produced through 2002. It carried over some parts from the light-duty Turbo-Hydramatic 200 and 350, but was generally a new design.

The 125 was renamed 3T40 later, following GM's new naming convention. The 4T40-E replaced it starting in 1995.

Applications:

[edit] Turbo-Hydramatic 125 C

This was a later model of the 125 that included an ECU controlled solenoid that would engage the torque converter into "lock up" where engine power was transferred directly to the axle. 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.

However, despite problems with the TCCs (which may be easily disconnected by a vehicle owner), THM 125 and 125C transmission have proven to be extremely durable over the lifetime of a vehicle.

[edit] Turbo-Hydramatic 440-T4

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.

One unique feature of this transmission is its use of both a modulator valve and a throttle valve (TV) cable. Most transmission 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 affect on the shift feel.

The 440-T4 was later renamed the 4T60.

The electronically-controlled 4T60-E was introduced in 1991. It would become the basis of the GM 4T65 transmission, still used today.

A heavy-duty version, the 4T60 HD was used for the 1989-1990 Pontiac Turbo Grand Prix.

Applications:

  • 4T60
    • 1988-1994 W platform
    • 1985-1993 H/C platform
    • 1985-1993 A platform
    • 1988-1990 Buick Riviera/Reatta
    • 1985-1990 Cadillac models
  • 4T60-HD
    • 1989-1990 Turbo Grand Prix
  • 4T60-E
    • 1997-1999 Buick Century
    • 1994-1996 A platform
    • 1991-1999 W platform (some models)
    • 1991-1993 Cadillac models
    • 1991-1997 H/C platform
    • 1990-1992 Oldsmobile Toronado
    • 1990-1993 Buick Reatta
    • 1990-1993 and 1996 Buick Riviera
    • 1994-1996 Corsica/Beretta
  • F-7

[edit] See also