BURNT INTERMEDIATE BAND DIAGNOSIS-125 TRANSMISSION

When diagnosing a burnt band and direct clutch condition, a possible cause might be a third accumulator check valve not seating properly. This allows the intermediate band to drag while the direct clutch is applied causing excessive friction.

When servicing THM 125-125C transmissions for a burnt band and direct clutch condition, order service package 8643964, which contains a new dual land third accumulator check valve and a conical spring, then refer to the following procedure.

SERVICE PROCEDURE

1. Remove the intermediate servo cover and gasket.

2. Remove the third accumulator check valve and spring.

3. Inspect the third accumulator valve bore for presence of the valve seat (Figure 1). Also, inspect for wear or damage to the seat.

4. Plug the feed and exhaust holes in the bore using petrolatum (Figure 1).

5. Replace the third accumulator check valve with a dual land check valve. Center the valve so as to seat it properly.

6. Leak test the valve seat by pouring solvent into the accumulator check valve bore. Check for a leak on the inside of the case. (A small amount of seepage is acceptable.)

7. If the valve leaks, tap the valve with a brass rod and rubber mallet, to try to re-seat the valve.

8. Re-leak test the valve seat.

9. If the valve continues to leak, it will be necessary to replace the case.

10. If the valve doesn't leak, remove the check valve and install the new conical valve spring onto the valve (small end first). Install the valve into the case bore (Figure 2).

11. Install the servo gasket and cover. (Do not use old gasket.)

All THM 125-125C transmissions being serviced for a burnt band and direct clutch condition must have the new dual land third accumulator check valve and conical spring installed.

For further causes of a burnt band and direct clutch condition, refer to Chevrolet Dealer Service Information Bulletin 81-I-52 as well as the service manual.

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.