DIAGNOSIS INFO ON THM 125C LO-REVERSE CLUTCH

MODELS/YEARS: ALL 1980-89 MODELS EQUIPPED WITH THM 125/125C/HYDRA-MATIC 3T40 TRANSAXLES (M34-MD9)

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:

Direct clutch drum center 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.

Driven sprocket support seals - check for improperly cut angles.

In Lo-Reverse Clutch area:

Rolled and/or cut lo-reverse clutch piston seals. Cup plug seal (improperly installed) or cut. Cut "O' ring seal on lo-reverse pipe. Bent and/or leaky lo-reverse pipe. Bent and/or missing lo-reverse pipe bracket.

Part Non Conformity:

Porosity in the #4 and #5 check ball area of the case cover (cross channel leak during 3rd gear apply).

#6 check ball not seated during apply.

Stuck boost valve.

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.