GM 125C (3T40) – ATSG (Automatic Transmission Service Group)
GM 125C (3T40) – ATSG (Automatic Transmission Service Group) PDF free online
This Repair Manual contains the general description, diagnosis and overhaul procedures necessary to repair, overhaul or service the THM 125C (3T40) transaxle. In addition to this booklet for the assembly and disassembly procedures, the Green “THM 125C Update Handbook” available from ATSG is also necessary to inform you of the many engineering changes that have occured over the years.
The THM 125C transaxle represents the addition of a converter clutch to the THM 125 transaxle that was introduced in 1980. The Torque Converter Clutch was added to increase fuel economy by eliminating the fluid coupling of the transmission at road load conditions, replacing it with a direct mechanical connection.
The torque converter smoothly couples the engine to the planetary gear system through three multiple disc clutch packs, one roller clutch and one band, to produce three forward speeds and reverse. Changing of the gear ratios and application of the converter clutch is controlled automatically.
Applications GM 125C (3T40):
- 1982–1996 A-body
- 1980–1985 X-body
- 1982–2002 J-body
- 1990-1993 W-body
- 1987–1996 L body
- 1990–1995 U-body vans (with LG6 engine)
- 1984-1988 Pontiac Fiero
- MAINTENANCE AND ADJUSTMENTS
- ON CAR SERVICE
- DIAGNOSIS AND REPAIR
- VALVE BODY
- TECHNICAL BULLETINS