FLEX PLATE CRACKING-REPLACE FLYWHEEL HOUSING/FLEX PLATE

SUBJECT: FLEX PLATE CRACKING (REPLACE FLYWHEEL HOUSING/FLEX PLATE)

VEHICLES AFFECTED: 1991 C5H-6H-7H B6 W/ALLISON AT545 A/T WITH 6.0L, 7.0L GAS ENGINE

Some 1991 medium duty trucks/buses equipped with 6.OL or 7.OL 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, which is non-concentric and can cause runout which exceeds 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

For B6: From TO -------- -------- GMC MV500001 MV501905

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, Flywheel 2

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.