DRIVE LINE STOP CLUNK-CLEAN AND LUBRICATE SLIP YOKE

SUBJECT: DRIVELINE STOP CLUNK

MODELS: 1988-91 C1, C2 LIGHT DUTY TRUCKS WITH 4L60 AND 3L80 AUTOMATIC TRANSMISSIONS

THIS BULLETIN CANCELS AND REPLACES GMC TRUCK SERVICE BULLETIN 89-T-98 (CORPORATE NUMBER 964101) DATED AUGUST, 1989 TO ADD 1990-91 MODEL YEARS AND TO UPDATE THE PART NUMBER. ALL COPIES OF 89-T-98 SHOULD BE DISCARDED.

GMC TRUCK RECOMMENDS THAT A COPY OF THIS BULLETIN ALSO BE FILED UNDER SECTION 7A-AUTOMATIC TRANSMISSION.

Normal driveline tension build-up is released following vehicle braking on some 1988-91 C1 and C2 models (with single piece propshafts and automatic transmissions) as driveline clunk when stopping. The tension build-up is the result of the driveshaft splines binding on the transmission slip yoke.

To eliminate stop clunk due to spline-yoke bind, the driveshaft splines should be lubricated with a special lubricant. This bulletin releases a new lubricant that has increased durability over the previously released lubricant.

NOTICE: This procedure should be applied to 1988-91 C1, C2 vehicles with automatic transmissions and one-piece propshafts only. When applied to other vehicles, possible transmission lube contamination could result.

SERVICE PROCEDURE

1. Remove driveshaft.

2. Clean slip yoke and inside of driveshaft spline with solvent and clean cloth.

3. Apply grease (P/N 12345879) to slip yoke spline with a brush or swab, so as to completely cover the entire spline with a light coating of grease.

4. Reinstall propshaft.

SERVICE PARTS INFORMATION

Part Number Description ---------- ------------------------------ 12345879 1 lb. can of special lubricant (should service about 50 vehicles)

Parts are currently available from GMSPO.

WARRANTY INFORMATION

For vehicles repaired under warranty use:

Labor Operation: T7995 Labor Time: 0.4 hr

NOTE: Labor Operation is coded to base vehicle coverage in the warranty system.

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.