PREMATURE BRAKE WEAR (REPLACE BRAKE PADS & ROTORS). Chevrolet Chevy MD Bus Chassis (B Model) 1992

SUBJECT: "PREMATURE" BRAKE WEAR (REPLACE BRAKE PADS AND ROTORS)

MODELS: 1990-96 CHEVROLET AND GMC MEDIUM DUTY TRUCKS WITH BENDIX HYDRAULIC BRAKES (RPO JE3) EXCLUDING FOUR PISTON REAR CALIPERS (RPO JNC), 8,100 LB. FRONT AXLE (RPO FL1) AND/OR 15,000 LB. REAR AXLE (RPOS H08 + H10)

CONDITION:

SOME CUSTOMERS MAY COMMENT ABOUT LESS THAN EXPECTED BRAKE PAD LIFE.

BRAKE PAD LIFE IS AFFECTED BY BRAKE USAGE, DUTY CYCLE, VEHICLE LOADING, DRIVER TRANSMISSION SHIFT HABITS AND DRIVING HABITS.

CORRECTION:

IN AN EFFORT TO PROVIDE THE CUSTOMER WITH INCREASED BRAKE PAD LIFE, A NEW THICKER BRAKE PAD AND THINNER ROTOR IS STANDARD FOR THE 1997 PRODUCTION YEAR. THE PAD'S THICKNESS IS INCREASED BY 2.03MM (0.080") AND THE ROTOR THICKNESS DECREASED BY 2.54 MM (0.100").

THE THICKNESS OF THE NEW ROTOR WEAR SURFACE REMAINS APPROXIMATELY THE SAME BUT THE INNER "FINNED" SECTION IS DECREASED IN SIZE MAKING THE 1997 ROTOR THINNER THAN PREVIOUS MODEL YEAR ROTORS.

IMPORTANT: THE NEW THINNER ROTOR/THICKER PAD DESIGN CANNOT BE USED ON TRUCKS EQUIPPED WITH THE OPTIONAL FOUR PISTON REAR DISC BRAKES (RPO JNC), THE 8,100 LB. FRONT (RPO JNC) AND/OR 15,000 LB. REAR (RPOS H08 OR H10) AXLES.

THIS CHANGE ONLY APPLIES TO VEHICLES EQUIPPED WITH BENDIX HYDRAULIC DISC BRAKES WITH THE DUAL 2.875 INCH CALIPER PISTON BORES IN THE AXLE COMBINATIONS LISTED BELOW.

NEW AND PAST MODEL ROTORS CAN BE IDENTIFIED BY THEIR THICKNESS. USING A MICROMETER, MEASURE THICKNESS ABOUT 25 MM (1 INCH) FROM THE EDGE OF THE ROTOR. NEW 1997 ROTORS SHOULD MEASURE ABOUT 36.45 MM (1.435 "). NEW PAST MODEL ROTORS SHOULD MEASURE ABOUT 39 MM (1.535").

AFTER THE DESIGN NEW ROTORS ARE WORN, IT MAY BE DIFFICULT TELLING THE DIFFERENCE BETWEEN THEM AND A PAST MODEL ROTOR. A MINIMUM DISCARD THICKNESS IS STAMPED INTO THE NEW ROTORS AS WELL AS THE PAST MODEL ROTORS, AND MAY PROVIDE THE NECESSARY INFORMATION NEEDED TO DISTINGUISH THE TWO. NEW 1997 BRAKE PADS SHOULD MEASURE AS SHOWN IN THE CHART BELOW.

IMPORTANT: INSTALL ONLY 1997 MODEL YEAR ROTORS AND PADS ON 1997 TRUCKS. WHEN USING THE NEW DESIGN ROTORS AND PADS ON 1996 AND OLDER TRUCKS, THEY MUST BE INSTALLED IN SETS. DO NOT INTERMIX PARTS.

SERVICE PROCEDURE:

REPLACE THE BRAKE ROTORS AND PADS FOLLOWING THE PROCEDURE DESCRIBED IN SECTION 5B1 OF THE APPROPRIATE YEAR AND MODEL SERVICE MANUAL.

PARTS INFORMATION:

AXLE CURRENT NOMINAL NEW DISCARD CAPACITY ROTOR # THICKNESS THICKNESS

FRONT 9/11/12K 12547785 1.435 IN. 1.320 IN. REAR 19K 12386718* 1.435 IN. 1.320 IN. REAR 21K 12386716 1.435 IN. 1.315 IN.

AXLE FORMER NOMINAL NEW DISCARD CAPACITY ROTOR # THICKNESS THICKNESS

FRONT 9/11/12K 15619970 1.535 IN. 1.420 IN. REAR 19K 15619970 1.535 IN. 1.420 IN. REAR 21K 15619626 1.535 IN. 1.415 IN.

CURRENT NOMINAL PAD KIT # THICKNESS

12547536 OUTER .916 IN. INNER 1.108 IN.

FORMER NOMINAL PAD KIT # THICKNESS

12544299 OUTER .876 IN. INNER 1.068 IN.

* SAME AS 12547785 EXCEPT IT HAS TAPPED HOLES FOR MOUNTING AN ABS RING.

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OP DESCRIPTION LABOR TIME SEE MEDIUM DUTY ROTOR REPLACE USE PUBLISHED LABOR TIME GUIDE PADS REPLACE LABOR OPERATION TIME

IMPORTANT: LABOR OPERATION IS CODED TO BASE VEHICLE COVERAGE IN THE WARRANTY SYSTEM.

FIGURES: 0

CAPTIONS: 0

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.