LOCKING REAR AXLE CHATTER (MAINT./WARRANTY INFO.)

SUBJECT: LOCKING REAR AXLE CHATTER

MODELS: ALL LIGHT DUTY TRUCKS EQUIPPED WITH LOCKING REAR AXLES, RPO G80

THIS BULLETIN CANCELS AND REPLACES GMC TRUCK SERVICE BULLETIN 90-4B-30 (CORPORATE NUMBER 964201) DATED JANUARY, 1990 TO ADD WARRANTY INFORMATION. ALL COPIES OF 90-4B-30 SHOULD BE DISCARDED.

Some light duty trucks equipped with locking rear axles (G80) may exhibit rear axle chatter, especially when turning a corner from a stop.

This condition of alternate engagement and disengagement of the clutches in the differential assembly is usually caused by contaminated axle lubricant.

To correct this condition, drain and refill the rear axle with SAE 80W-90 GL5 (P/N 1052271). The use of any additive in locking rear axles (G80) is not recommended. Rear axle additives are designed for use in limited slip differentials which are normally installed in cars. All light duty trucks equipped with RPO G80 make use of a locking differential and the use of additives will delay the engagement of the locking mechanism and may decrease axle life.

VEHICLES/COMPONENTS INVOLVED: ----------------------------- Some light duty trucks equipped with locking rear axles, RPO G80.

SERVICE PARTS INFORMATION:

Part Number Description ------------ ------------------------ 1052271 Lubricant, Rear Axle (24 oz.) See Appropriate Gasket, Rear Axle Housing Parts Manual Cover

Parts are currently available through GMSPO.

WARRANTY INFORMATION:

As specified in Light Duty Truck Maintenance Schedules, locking rear axle fluid drain and refill is required owner maintenance at the first engine oil change. Failure to drain and refill the rear axle as specified may contribute to a later axle chatter condition. Refer to the appropriate Light Duty Truck Maintenance Schedule or service manual, section 0B, for further details on change intervals.

For those vehicles repaired under warranty, which have had the axle fluid changed at the first oil change and have experienced rear axle chatter use:

Labor Operation: F2010, Locking Differential - Flush

Labor Time: 0.9 hr. (All Models)

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.