LOCKING DIFFERENTIAL CHATTER NEW CARRIER ASSY.PART NO.

A CONDITION MAY EXIST WHERE THE EATON 8 1/2 INCH LOCKING DIFFERENTIAL MAY EXHIBIT A CHATTER CONDITION ON ACCELERATION FROM A STOP. THIS IS MOST LIKELY TO OCCUR WHEN THE DIFFERENTIAL IS HOT, AFTER EXTENDED HIGHWAY DRIVING. THE 8 1/2 INCH EATON LOCKING DIFFERENTIAL WAS REDESIGNED INTERIM THE 1985 MODEL YEAR TO ALLEVIATE CHATTER. THE BELL END CLUTCH PACK HAS BEEN CHANGED FROM SEVEN DISCS TO FIVE THICKER DISCS. THIS CHANGE IS EFFECTIVE FOR AXLE DATE CODES OF JANUARY 22, 1985, (022) AND LATER. THE DATE CODE CAN BE FOUND STAMPED ON TOP OF THE RIGHT AXLE TUBE OUTBOARD OF THE CARRIER, PRECEDED BY FOUR ALPHA NUMERIC CHARACTERS REPRESENTING THE AXLE AND SOURCE CODES. COMPARE THE AXLE CODE STAMPED ON THE AXLE TUBE WITH THE CORPORATE AXLE CODES IN THE GM PARTS BOOK TO DETERMINE IF YOU HAVE AN 8 1/2 INCH EATON LOCKING DIFFERENTIAL. NOTE THAT AXLE CODES CHANGE FOR EACH MODEL YEAR. EXAMPLE: BN3 G 001 1 --- ----- ------- ------- AXLE CODE SOURCE CODE DATE CODE SHIFT CODE THE NEW DIFFERENTIAL CASE ASSEMBLY PART NUMBER IS 26005119, AND THE NEW FIVE DISC BELL END PLATE KIT CAN BE ORDERED USING PART NUMBER 15580825. THE FIVE AND SEVEN DISC PLATE KITS ARE INTERCHANGEABLE. IF A VEHICLE EQUIPPED WITH AN EATON 8 1/2 INCH LOCKING DIFFERENTIAL WITH A DATE CODE PRIOR TO 022, 1985, EXPERIENCES CHATTER, REPLACE THE BELL END CLUTCH PACK AS DESCRIBED IN THE SERVICE PROCEDURE BELOW. SERVICE PROCEDURE ----------------- FOLLOW THE UNIT REPAIR PROCEDURE FOR THE 8 1/2 INCH LOCKING DIFFERENTIAL FOUND ON PAGE 4B6-4 THROUGH 4B6-7 IN THE 1985 LIGHT DUTY TRUCK SERVICE MANUAL. A) REPLACE THE RIGHT HAND (BELL END) CLUTCH PACK WITH THE NEW CLUTCH PACK, P/N 15580825. NOTE: IF THE ENTIRE CARRIER ASSEMBLY REQUIRES REPLACEMENT, INSTALL THE NEW DIFFERENTIAL CASE ASSEMBLY, P/N 26005119. B) REFILL WITH THE RECOMMENDED LUBRICANT ONLY, GM PART NUMBER 1052271, OR EQUIVALENT. DO NOT ADD LIMITED SLIP ADDITIVE, GM P/N 1052358, TO THE -------------------------------------------------------- DIFFERENTIAL FLUID. THIS PRACTICE DELAYS THE ENGAGEMENT ------------------- OF THE LOCKING MECHANISM, AND CAN BE DETRIMENTAL TO THE LIFE OF THE AXLE. ****GMC/CHEV DISCLAIMER****

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.