ALLISON A/T FRT. PUMP SEAL LEAKAGE-REVISED PART RELEASED

SUBJECT: ALLISON A/T FRONT PUMP SEAL LEAKAGE

VEHICLES AFFECTED: 1987-88 C5, C6, C7, B6, P6, S7 W/ALLISON AT545 TRANS (MF1) AND 6.OL/7.OL GAS ENG (VIN CODE B AND E)

Some 1987-88 medium duty trucks/buses equipped with 6.0L or 7.0L gasoline engines and AT545 Allison Automatic Transmissions, may experience oil leakage at the transmission front pump seal. This condition may be the result of an improperly manufactured engine flex plate, which causes the torque converter to move too far rearward (towards the transmission) and the pump oil seal to run on the unmachined surface of the torque converter. When this occurs, the seal may become damaged and leak fluid (Figure 1).

Effective May 16, 1988, all subject vehicle engines are manufactured with properly manufactured flex plates. The engine manufacturing date can be determined by the engine code, located on a machined boss just behind the engine water pump (Figure 2).

All out of specification material at CANSPO has been purged effective May 16, 1988. Inspected service stock can be identified by a color code painted on the face of flex plate. Listed below are the two color codes used, which is determined by the engine size.

ENGINE COLOR CODE ------ ---------- 6.0L (366) Black "X"

7.0L (427) White "X"

If a leaking or damaged transmission front pump seal is encountered, the engine flex plate must be replaced since there is no way to easily determine if the plate is within specifications. The replacement plate received from CANSPO should be color coded as indicated above.

NOTE: All Allison Transmission repairs, including transmission seal replacement must be performed by an authorized Allison overhaul dealer or distributor.

Repair Procedure:

There are several options available, depending on individual dealership capabilities and warranty authority:

1. If GMC Truck/Chevrolet Dealer is an authorized Allison Automatic Transmission overhaul Dealer:

A. Remove transmission and replace engine flex plate (refer to Medium Duty Service Manual, Section 7A, for transmission removal and installation instructions).

B. Remove and reinstall front transmission seal. When existing seal is removed, inspect for oil pump seal cavity scoring due to the seal spinning. (Refer to Allison Automatic Transmission Manual AT540 Series, Section 6, for installation instructions).

2. If GMC Truck/Chevrolet Dealer is not an authorized Allison Automatic Transmission Overhaul Dealer, two alternative courses of action may be taken:

A. 1. Contact local authorized Allison Automatic Transmission Overhaul Dealer or distributor to have engine flex plate and transmission oil seal replaced, and oil pump cavity checked for scoring.

-OR-

B. 1. Remove transmission from truck and replace engine flex plate.

2. Contact local authorized Allison Automatic Transmission Overhaul Dealer or distributor to have front transmission oil seal repaired and oil pump seal cavity inspected for scoring due to the seal spinning.

3. Reinstall repaired transmission.

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.