INFORMATION ON SERVICING THE NEW BRAKE SYSTEM

REVISION: 07/21/94

THIS BULLETIN IS BEING REVISED TO CORRECT THE VIN BREAKPOINTS.

SUBJECT: INFORMATION ON SERVICING THE NEW C3500HD BRAKE SYSTEM

MODELS: 1994 CHEVROLET AND GMC TRUCK C3500HD MODELS BUILT STARTING WITH THE FOLLOWING VIN BREAKPOINTS:

CHEVROLET 1GBKC34F9RJ107933 GMC TRUCK 1GDKC34FXRJ514540

A NEW BRAKE SYSTEM WENT INTO PRODUCTION ON C3500HD MODELS BEGINNING WITH THE ABOVE MENTIONED BREAKPOINTS. THE CHANGES WERE MADE TO IMPROVE BRAKE WEAR CHARACTERISTICS OF THE VEHICLE. CHANGES TO THE BRAKES INCLUDE NEW FRONT AND REAR ANCHOR PLATES, NEW FRONT HUBS, NEW BRAKE ROTORS, AND A 130 PERCENT INCREASE IN BRAKE PAD VOLUME OVER THE PREVIOUS RIVETED CONSTRUCTION BRAKE PADS.

NOTICE: THE NEW BRAKE PARTS ARE NOT INTERCHANGEABLE WITH THE OLDER BRAKES EXCEPT FOR COMPLETE ASSEMBLIES. A SERVICE KIT IS BEING DEVELOPED TO ADDRESS SERVICE CONCERNS ON MODELS BUILT PRIOR TO THE VIN BREAKPOINT.

WHEN SERVICING THE BRAKES ON A C3500HD MODEL BUILT AFTER THE VIN BREAKPOINT GIVEN ABOVE, THE FOLLOWING INFORMATION WILL BE HELPFUL.

- THERE IS NO ANTI-RATTLE SPRING ON THE NEW BRAKE PADS. DO NOT ATTEMPT TO USE THE OLD BRAKE PAD ANTI-RATTLE SPRING ON THE NEW BRAKE PADS AS THE INNER PAD MAY BIND IN THE ANCHOR PLATE RESULTING IN INCREASED WEAR OF THE INNER PAD.

- THERE IS NO WEAR SENSOR ON THE NEW BRAKE PADS. BRAKE PAD WEAR SHOULD BE CHECKED AT REGULAR INTERVALS.

- A NEW CALIPER LOCK (P/N 15501013) AND CALIPER SPRING (P/N 15501010) ARE NOW USED TO RETAIN THE CALIPER. THE OLD CALIPER LOCK AND CALIPER SPRING DO NOT PROPERLY FIT THE NEW CALIPER ANCHOR PLATE.

- AEROSHELL #5 GREASE SHOULD BE APPLIED TO THE CALIPER V-WAYS AND ANCHOR PLATE GUIDE WAY SURFACES AT REGULAR MAINTENANCE INTERVALS. AEROSHELL #5 GREASE CAN BE OBTAINED AT LOCAL SHELL DISTRIBUTORS.

WE BELIEVE THIS SOURCE AND THEIR PRODUCT TO BE RELIABLE. THERE MAY BE ADDITIONAL MANUFACTURERS OF SUCH PRODUCTS. GENERAL MOTORS DOES NOT ENDORSE, INDICATE ANY PREFERENCE FOR OR ASSUME ANY RESPONSIBILITY FOR THE PRODUCTS FROM THESE FIRMS OR FOR ANY SUCH ITEMS WHICH MAY BE AVAILABLE FROM OTHER SOURCES.

- DO NOT USE "NEVER SEIZE" TYPE PRODUCTS ON THE CALIPER V-WAYS AND ANCHOR PLATE GUIDE WAY SURFACES. THESE PRODUCTS ARE NOT LUBRICANTS AND RESULT IN HIGH CALIPER SLIDE FORCES WHICH CAN CAUSE INCREASED WEAR OF THE BRAKE PADS.

- WHEN INSTALLING NEW BRAKE PADS ONTO THE CALIPER, THE FOLLOWING CRIMPING PROCEDURE SHOULD BE FOLLOWED IN ORDER TO PROPERLY SECURE THE OUTER BRAKE PAD TO THE CALIPER. WHEN PROPERLY INSTALLED, THERE SHOULD BE NO LOOSENESS OF THE BRAKE PAD IN THE CALIPER. 1. PLACE THE NEW BRAKE PAD IN A VISE AS SHOWN IN FIGURE 1.

2. COMPRESS THE VISE AS NECESSARY IN ORDER TO OBTAIN A SECURE FIT BETWEEN THE OUTER BRAKE PAD AND THE CALIPER (FIGURE 2).

3. INSTALL THE OUTER BRAKE PAD ONTO THE CALIPER. IF NECESSARY, USE A C-CLAMP TO INSTALL THE PAD ONTO THE CALIPER. DO NOT ALLOW THE C-CLAMP TO COME INTO CONTACT WITH THE LINING, RATHER, INSERT A USED BRAKE PAD BETWEEN THE C-CLAMP AND THE NEW BRAKE PAD LINING (FIGURE 3).

4. IF NECESSARY, FILE THE LEADING EDGE OF THE BRAKE PAD TANG AS SHOWN IN FIGURE 4 TO AID IN INSTALLING THE BRAKE PAD TO THE CALIPER.

NOTICE: IF THE OUTER BRAKE PAD IS NOT SECURELY INSTALLED ONTO THE CALIPER, A BRAKE RATTLE CONDITION MAY RESULT.

- THE FRONT AND REAR BRAKE ROTOR DISCARD THICKNESSES HAVE BEEN REVISED AS FOLLOWS:

MINIMUM REFINISHING ORIGINAL THICKNESS THICKNESS DISCARD THICKNESS 36.26 - 36.64 MM 35.1 MM 34.7 MM (1.428 - 1.443 IN.) (1.382 IN.) (1.366 IN.)

- ATTACHING FASTENERS AND TORQUE SPECIFICATIONS HAVE CHANGED ON SEVERAL FASTENERS. THE CORRECT TORQUE SPECIFICATIONS FOR ALL THE FASTENERS ARE AS FOLLOWS:

CALIPER LOCK MOUNTING BOLT 20 N.M (15 LBS. FT.) FRONT ANCHOR PLATE TO KNUCKLE NUT 257 N.M (190 LBS. FT.) FRONT SPLASH SHIELD BOLT 16.5 N.M (12 LBS. FT.) FRONT ROTOR TO HUB BOLT 237 N.M (175 LBS. FT.) REAR ANCHOR PLATE TO AXLE FLANGE NUT 105 N.M (78 LBS. FT.)

FIGURES: 4

CAPTIONS: FIGURE 1 - CRIMPING THE OUTER BRAKE PAD FIGURE 2 - OUTER BRAKE PAD PROPERLY SECURED TO THE CALIPER FIGURE 3 - INSTALLING THE OUTER BRAKE PAD FIGURE 4 - FILING THE LEADING EDGE OF THE OUTER BRAKE PAD TANG

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.

COPYRIGHT 1994 GENERAL MOTORS CORPORATION. ALL RIGHTS RESERVED.