FLEX PLATE CRACKING-REPLACE FLYWHEEL HOUSING/FLEX PLATE

SUBJECT: ALLISON AUTOMATIC TRANSMISSION FLYWHEEL (FLEX PLATE) CRACKING

MODELS: 1991 C5H/C6H/C7H/B6/P5/P6/S7 WITH ALLISON AT545 TRANSMISSION (MFI) AND 6.0L/7.0L GAS ENGINE (VIN CODE M,P)

Some 1991 medium duty trucks equipped with 6.0L or 7.0L gasoline engines and AT545 Allison Automatic Transmissions, may experience flex plates that crack around bolt circle at crankshaft causing noise. This condition may be the result of an improperly manufactured flywheel housing, that is non-concentric and can cause runout exceeding GM specifications. When this occurs, both the engine flywheel housing and the flex plate MUST BE replaced.

VEHICLES INVOLVED:

Effective June 17, 1991, all subject vehicles are manufactured with properly manufactured engine flywheel housings. The vehicles involved were produced between the following VIN breakpoints.

For C5H, C6H, AND C7H From TO ----------- ------- -------- GMC MJ500018 MJ520954 Chevrolet MJ100114 MJ110420

For B6 From TO ------- -------- --------- GMC MV500001 MV501905 Chevrolet MV100001 MV103725

SERVICE PROCEDURE:

Refer to Section 6A-8 (Flywheel Replacement) of the appropriate 1991 service manual for flex plate and flywheel housing service information.

SERVICE PARTS INFORMATION:

Part Number Description Quantity -------- ------------------ -------- 15647398 Housing, Flywheel 1 10114196 Flywheel (Flex Plate) 1 462619 Retainer, heel 2

Parts are expected to be available on 9-2-91. Until then normal part orders will not be accepted by GMSPO. Only verifiable emergency VIP orders will be accepted. SPO will make every effort to obtain parts. All parts will be placed on 400 control to waive VIP surcharges. However, the part will be shipped premium transportation at dealer's expense. All other order types will be canceled as incorrectly ordered while the 400 control is in place.

WARRANTY INFORMATION:

For vehicles repaired under warranty use: Labor Operation: K7040 Labor Time: 3.7 hrs. Add: 0.4 hr. with PTO

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.