For 1990-2009 cars

# DIAGNOSIS INFO ON THM 125C LO-REVERSE CLUTCH

TRANSMISSION MODELS: VEHICLE APPLICATIONS: ALL 1980-1989 MODELS A,J,L,N,T, CARS

#### Bulletin Covers:

Diagnosis information given for possible inoperative Lo-Reverse Clutch assembly used in the THM 125C/HYDRA-MATIC 3T40 transaxle.

Causes for an inoperative Lo-Reverse assembly are as follows:

#### In the Direct Clutch area:

o Direct Clutch Drum Centre Seal that is rolled and/or cut.

This condition would cause a cross circuit leak that would apply (drag) the Lo-Reverse clutch each time the vehicle is driven in the third gear range.

o Driven Sprocket Support Seals - check for improperly cut angles.

In Lo-Reverse Clutch area:

o Rolled and/or cut Lo-Reverse clutch piston seals. o Cup Plug Seal (improperly installed) or cut. o Cut "O" Ring Seal on Lo-Reverse Pipe. o Bent and/or Leaky Lo-Reverse Pipe. o Bent and/or Missing Lo-Reverse Pipe Bracket.

#### Part Non Conformity:

o Porosity in the #4 and #5 Check ball area of the case cover (cross channel leak during 3rd gear apply). o #6 Check ball not seated during apply. o Stuck Boost Valve. o Backing plate out of location.

Whenever a suspect LO-Reverse condition exists all of the previous items should be inspected and/or replaced if necessary.

#### SERVICE MANUAL REFERENCE:

Whenever service to the Lo-Reverse Clutch Assembly is necessary refer to the THM 125C/HYDRA-MATIC 3T40 Unit Repair Section of your Service Manual.

#### SERVICE NOTES:

The Direct Clutch in the THM 125C/HYDRA-MATIC 3T40 is only applied in 3rd gear and Reverse - the Reverse Clutch is on in the Manual Lo and Reverse gear ranges. If a Lo-Reverse condition exists the Direct Clutch assembly should be inspected and all components discussed under Bulletin Covers.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.