The 3-speed General Motors 3T40, also known as the TH125 or M34, automatic transmission debuted in 1979, was installed on front-wheel-drive models. It was also known as the transmission found in older Opels. In 1982, a new version with a torque converter, designated the TH125C or MD9, was released.
Specifications
| Type | automatic transmission |
| Number of gears | 3 |
| Type of drive | front |
| Engine volume, l | up to 3.1 |
| Torque output, Nm | up to 258 |
| Recommended oil | ATF Dexron VI |
| Oil capacity, liter | 8.5 |
| Partial replacement, liter | 3.8 |
| Maintenance | every 80 000 km |
| Gearbox lifespan, km | ~400 000 km |
| Weight, kg | 58 |
Gear ratios GM 3T40
Using the example of a 1986 Opel Ascona with a 1.6 liter engine:
| Main | 3.74 |
| 1st | 2.84 |
| 2nd | 1.60 |
| 3rd | 1.00 |
| Reverse | 2.07 |
Using
The transmission was installed on:
- Buick Century 5 in 1981 – 1996;
- Buick Skyhawk 2 in 1981 – 1989;
- Buick Skylark 4 in 1979 – 1985;
- Cadillac Cimarron 1 in 1981 – 1988;
- Chevrolet Beretta 1 in 1987 – 1996;
- Chevrolet Cavalier 1 in 1981 – 1987;
- Chevrolet Cavalier 2 in 1987 – 1994;
- Chevrolet Cavalier 3 in 1994 – 2001;
- Chevrolet Celebrity 1 in 1981 – 1990;
- Chevrolet Citation 1 in 1979 – 1985;
- Chevrolet Corsica 1 in 1986 – 1996;
- Chevrolet Lumina 1 in 1989 – 1994;
- Chevrolet Lumina APV 1 (GMT199) in 1989 – 1996;
- Daewoo Cielo 1 in 1994 – 2002;
- Daewoo LeMans 1 in 1986 – 1994;
- Daewoo Racer 1 in 1986 – 1994;
- Daewoo Racer 2 in 1994 – 1997;
- Isuzu Aska 1 (JJ) in 1983 – 1989;
- Oldsmobile Ciera 1 in 1981 – 1996;
- Oldsmobile Firenza 1 in 1982 – 1988;
- Oldsmobile Omega 3 in 1979 – 1984;
- Oldsmobile Silhouette 1 (GMT199) in 1989 – 1996;
- Opel Ascona C (J82) in 1981 – 1988;
- Pontiac Fiero 1 in 1983 – 1988;
- Pontiac Grand Prix 6 in 1987 – 1996;
- Pontiac Phoenix 2 in 1979 – 1984;
- Pontiac Sunfire 1 in 1994 – 2001;
- Pontiac Sunbird 2 in 1981 – 1987;
- Pontiac Sunbird 3 in 1988 – 1994;
- Pontiac Trans Sport 1 (GMT199) in 1990 – 1996.
Disadvantages of the GM 3T40 gearbox
- This is a simple, very reliable, and durable automatic transmission;
- The main thing is to carefully monitor for oil leaks, which occur regularly;
- Damaged wiring or electrical connectors are also a common cause of failure;
- At high mileage, chain stretching and sometimes even breaks are common;
- It’s worth noting that the service life of an automatic transmission depends heavily on the combination with an R4 or V6 engine.
