Turbo-Hydramatic 125
motor vehicle
The Turbo-Hydramatic 125 (modern designation 3T40) was the first in a line of automatic transmissions from General Motors designed for transverse engine application. Introduced in 1980 in the X-body and T-body (FWD) platform vehicles the units were used across all of GMs divisions worldwide, and was augmented by later automatic four speed transaxles, starting with the 44T-4 (4T60) which bore no internal functional resemblance to the original design 3 speed transaxle other than its basic chain driven 180-degree rotated version of its longitudinally mounted Stromberg THM 180 incarnation.
Turbo-Hydramatic 125
The 3-speed Turbo-Hydramatic 125 was introduced in 1980 and produced through 2001. 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. After the 1995 introduction of the electronically controlled 4T40-E 4-speed, the 3T40 was gradually phased out.
Applications:
1982–1996 A-body
1980–1985 X-body
1982–2001 J-body
1990-1993 W-body
1987–1996 L body
1980-1991 T-body (FWD)/T80
1990–1995 U-body vans (with LG6 engine)
1984-1988 Pontiac Fiero
Turbo-Hydramatic 125 C
This was a later model of the 125 that debuted for 1982 and included a torque converter clutch or TCC. The TCC acts similar to a clutch in a manual transmission vehicle, in that at speeds above 35 MPH a combination of engine vacuum- and temperature-sensing valves, and a dedicated brake switch - and in later models an ECU - activated a solenoid which engaged a clutch physically locking the impeller and turbine inside the torque converter together causing engine power to be transferred directly to the transaxle. The C in Turbo-Hydramatic 125 C denoted the use of a TCC. The solenoid that controls this is notorious for failure due to overheated plastic componentry, and problems indicated by an engine stall when stopping from speeds greater than 45 MPH. This occurs because the clutch does not disengage, and as the affected vehicle's speed nears zero miles per hour, the engine is forced to decelerate to zero rpm.
Turbo-Hydramatic 125 C AWD
For the 1988 model year, the Pontiac Division of GM utilized a THM 125C modified to accommodate a full-time All-Wheel-Drive planetary gear transfer case and output housing to send 40% of the output torque to the rear wheels in the 3.1 liter powered 6000STE. While a similar design was used for the later 4T65E, the three speed design was utilized for only three model years, after which all-wheel drive was discontinued as an option for the car line.
Turbo-Hydramatic 440-T4
The model THM440T4 indicates Turbo HydraMatic Model 440, Transversely Mounted, 4 Speed Fully Automatic transaxle (complete new design as an in-place upgrade from THM 125/125C).
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