CLUTCH DRIVEN PLATE CRACKS (BORG & BECK 13 IN. CLUTCH ASS. GMC Truck GMC MD Conventional 97.5" 1988

************************************ THIS IS A GMC TRUCK DCS MESSAGE ************************************

SUBJECT: CLUTCH DRIVEN PLATE CRACKS BORG AND BECK 13" CLUTCH, ASSEMBLY P/N 14081001 ----------------------------------------------- MODELS: 1986-88 B6, C5, C6, C7, P4, P6 WITH 350/366 GAS ENGINES

CLUTCH DRIVEN PLATE CRACKING ON THE ABOVE MODELS MAY BE ATTRIBUTED TO TWO FACTORS:

A. EXCESSIVE CLUTCH HOUSING RUNOUT B. CLUTCH DRIVEN PLATE SPRING WINDOW OPENINGS

CLUTCH HOUSING RUNOUT HAS BEEN DETERMINED TO BE THE SIGNIFICANT FACTOR CONTRIBUTING TO DRIVEN PLATE FRACTURE. IT IS RECOMMENDED THE CLUTCH HOUSING BE MEASURED FOR RUNOUT AS FOLLOWS:

1. FLYWHEEL HOUSE BORE (PILOT) - MEASURE THE INSIDE OF THE HOUSING BY DIAL INDICATING FROM THE CRANKSHAFT HUB. TOTAL RUNOUT SHOULD NOT EXCEED .020" FOR BOTH SAE 1 AND 2 HOUSINGS.

2. ENGINE FLYWHEEL HOUSING FACE RUNOUT - MEASURE THE FACE OF THE HOUSING INDICATING FROM THE CRANKSHAFT HUB. TOTAL RUNOUT SHOULD NOT EXCEED .010" FOR BOTH HOUSINGS.

3. FLYWHEEL FACE RUNOUT - MEASURING FROM THE HOUSING TO THE EDGE OF THE FLYWHEEL SURFACE, TOTAL RUNOUT SHOULD NOT EXCEED .0005" FOR EACH INCH OF FLYWHEEL DIAMETER. FOR A 14" FLYWHEEL, MAX RUNOUT (WOBBLE) IS .007".

SPECIAL ATTENTION SHOULD BE PAID TO ALL MOUNTING SURFACES FOR ANY IRREGULARITIES CONTRIBUTING TO MISALIGNMENT. FAILURE TO CHECK THE ABOVE RUNOUTS MAY RESULT IN COMEBACKS.

THE CLUTCH DISC MANUFACTURER, BORG AND BECK, HAS CHANGED ITS DESIGN BY INCREASING THE CORNER RADIUS OF THE PLATE DAMPENER SPRING WINDOWS. ASSEMBLIES DATE CODED OCTOBER, 1986, AND LATER HAVE AN INCREASED SPRING WINDOW CORNER RADII. A THREE DIGIT CODE STAMPED BETWEEN THE WINDOWS IDENTIFIES THE BUILD DATE, IE., OCTOBER 1, 1986, WOULD APPEAR AS "1", "K", "6".

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.