DIAGNOSIS INFO ON THM 125C LO-REVERSE CLUTCH

Model and Year 1980-89 A, J, L CARS WITH 125C HYDRA-MATIC 3T40 TRANSAXLES

TO: ALL CHEVROLET DEALERS

This bulletin provides diagnosis information for possible inoperative Lo-Reverse Clutch assemblies 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 Seals (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.

Parts 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.

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.