REAR BRAKE SELF ADJUSTERS INOP INSPECT & ADJUST AS NEEDED

AUTOMATIC SLACK ADJUSTERS ARE DESIGNED TO AUTOMATICALLY ADJUST THE FOUNDATION BRAKE SYSTEM TO COMPENSATE FOR NORMAL BRAKE LINING WEAR. BY SELF ADJUSTING, DESIGNED BRAKE PERFORMANCE IS ALWAYS MAINTAINED. IT HAS BEEN DETERMINED THAT ON SOME VEHICLES BUILT PRIOR TO VIN BREAKPOINTS LISTED BELOW, THE SLACK ADJUSTERS MAY NOT HAVE BEEN SET UP PROPERLY AT ASSEMBLY, CAUSING A POTENTIAL OF SLACK ADJUSTERS NOT MAINT TAINING ADJUSTMENT.

CHEVROLET (MEDIUM DUTY) 1GBM7B1Y4JV102239 GMC (MEDIUM DUTY) 1GTK7D1F7JV502670 (HEAVY DUTY) 1GDT9C4Z7JV601273 VEHICLES MANUFACTURED WITH AUTOMATIC SLACK ADJUSTERS AND UNABLE TO MAINTAIN PROPER BRAKE ADJUSTMENT SHOULD BE INSPECTED TO DETERMINE IF THE CLEVIS SET-UP DIMENSION IS AS SPECIFIED IN TABLE 2. IF ACTUAL MEASUREMENTS ARE DIFFERENT, THEN A BRAKE ADJUSTMENT IS REQUIRED AS DESCRIBED BELOW.

. NOTICE: THE CLEVIS SET-UP DIMENSIONS AS SHOWN IN TABLE 2 DIFFER FROM THE DIMENSIONS GIVEN IN THE MEDIUM AND HEAVY DUTY SERVICE MANUALS. THE DIMENSIONS GIVEN IN THE SERVICE MANUALS SHOULD BE DISREGARDED.

SERVICE PROCEDURE

REFER TO THE MEDIUM DUTY SERVICE MANUAL X-8733 OR THE HEAVY DUTY SERVICE MANUAL X-8734, SECTION 5, FOR FURTHER REMOVAL OR INSTALLATION INSTRUCTIONS ON AIR BRAKE COMPONENTS.

MEASURE THE CLEVIS SET-UP DIMENSION AT ALL WHEEL LOCATIONS EQUIPPED WITH AUTOMATIC SLACK ADJUSTERS.

. BLOCK THE VEHICLE WHEELS.

. CHARGE AIR SYSTEM TO 120 PSI.

. MEASURE THE DISTANCE FROM THE CENTER OF THE SLACK ADJUSTER CLEVIS PIN TO THE FACE OF THE BRAKE CHAMBER WITH THE BRAKES IN THE UNAPPLIED POSITION (FIGURE NO. 1). IT IS IMPORTANT THAT THIS MEASUREMENT BE TAKEN FROM BRAKE CHAMBER FACE AND NOT FROM THE BRAKE CHAMBER MOUNTING BRACKET. THIS CLEVIS SET-UP DIMENSION SHOULD BE AS SPECIFIED IN TABLE 2.

. IF THE CLEVIS SET UP DIMENSION IS INCORRECT, LOOSEN THE SLACK ADJUSTER JAM NUT (32) AND COLLAR (22) (FIGURE 1) ON THE PUSHROD UNTIL THE CLEVIS SET-UP DIMENSION IS ACHIEVED. IF THE PUSHROD IS TOO LONG (PROTRUDES THROUGH COLLAR MORE THAN .125 IN), A CLEVIS ADJUSTMENT CANNOT BE MADE WITHOUT THE PUSHROD CONTACTING THE SLACK ADJUSTER, THEREFORE, THE PUSHROD MUST BE SHORTENED. THIS WILL REQUIRE REMOVAL OF THE SPRING BRAKE CHAMBER IF SO EQUIPPED. REFER TO SECTION 5B2, AIR FOUNDATION BRAKES, OF THE MEDIUM DUTY SERVICE MANUAL X-8733 OR THE HEAVY DUTY SERVICE MANUAL, X-8734, FOR CHAMBER REMOVAL INSTRUCTIONS.

. THE PUSHROD LENGTH, AS MEASURED FROM THE BRAKE CHAMBER TO THE END OF THE PUSHROD WITH CHAMBER FULLY RELEASED, MUST BE 38.1 MM (1.50 IN). CUT PUSHROD TO THIS DIMENSION.

. REINSTALL BRAKE CHAMBER ON THE VEHICLE AND ADJUST THE CLEVIS TO THE DIMENSION IN TABLE 2. TIGHTEN THE JAM NUT (32) AGAINST THE COLLAR (22).

NOTICE: DO NOT TURN THE MANUAL ADJUSTING NUT CLOCKWISE WITHOUT REMOVING THE PRESSURE RELIEF SCREW. DAMAGE WILL OCCUR TO THE PAWL SPRING AND ADJUSTING PAWL.

LABOR TIME:

SLACK ADJUSTER INSPECTION AND ADJUSTMENT

SINGLE REAR AXLE UNITS .5 HR (INCLUDING FRONT) TANDEM REAR AXLE UNITS .7 HR (INCLUDING FRONT) SHORTEN PUSH ROD .4 HR PER CHAMBER

TABLE 2 CLEVIS SET-UP DIMENSION -----------------------

FRONT AXLES

MEASUREMENT BRAKE SIZE + SLACK-ADJUSTER (FIGURE 1) AXLE MANUFACTURER MANUFACTURER + MM IN TYPE ------- ------------ --------------- -------------

7,000 LBS 15 X 4 ROCKWELL - AUTO 70 2 3/4 ROCKWELL

7,500 LBS 15 X 5 ROCKWELL - AUTO 70 2 3/4 ROCKWELL

9,000 LBS 15 X 4 ROCKWELL - AUTO 154 6 ROCKWELL

12,000 LBS 15 X 4 ROCKWELL - AUTO 154 6 (F120) ROCKWELL

12,000 LBS 15 X 4 ROCKWELL - AUTO 70 2 3/4 (FF941) ROCKWELL

12,000 LBS 16 X 5 X 5 ROCKWELL - AUTO 70 2 3/4 ROCKWELL

20,000 LBS 16.5 X 5/6 ROCKWELL - AUTO 70 2 3/4 ROCKWELL

REAR AXLES

ALL AXLES 16.5 DIA ROCKWELL - AUTO 68 2 11/16 ROCKWELL

16.5 DIA ROCKWELL-AUTO 72 2 13/16 EATON

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.