REVISED LEVER - HEIGHT SENSING PROPORTION VALVE-SERVICE PROC.. GMC Truck GMC C Pickup

REVISION: 07/30/96

THIS BULLETIN IS BEING REVISED TO ADD 1992-94 MODEL YEARS. PREVIOUS DIVISIONAL PUBLICATION NUMBERS WERE: CHEVROLET 91-374-3D GMC 91-5-128 GM OF CANADA 91-5-138 **********************************************************************

SUBJECT: REVISED LEVER ON HEIGHT SENSING PROPORTIONING VALVE (SERVICE PROCEDURE)

MODELS: 1991-94 CHEVROLET AND GMC C 3500 HEAVY DUTY MODELS

1991-94 C 3500 HD SERIES ARE EQUIPPED WITH A REAR SUSPENSION HEIGHT SENSING DEVICE WHICH OPTIMIZES THE BRAKE PROPORTIONING VALVE SETTING FOR THE LOAD THE VEHICLE IS CARRYING. THE HEIGHT SENSING SYSTEM "FINE TUNES" THE BRAKE BALANCE IN VEHICLES SUBJECTED TO A RANGE OF LOADING CONDITIONS.

OCCASIONALLY, VEHICLE MODIFICATIONS BY BODY BUILDERS OR OWNERS INFLUENCE THE HEIGHT SENSING DEVICE. IF A VEHICLE HAS HAD REAR SUSPENSION MODIFICATIONS WHICH AFFECT ITS TRIM HEIGHT OR SPRING RATE, AND THE DRIVER COMMENTS ABOUT THE BRAKE MODULATION CHARACTERISTICS OF THE VEHICLE, IT IS RECOMMENDED THAT THE HEIGHT SENSING SYSTEM BE REVISED AS DESCRIBED BELOW:

SERVICE PROCEDURE (FIGURES 1-4):

1. REMOVE LOAD VALVE LEVER ASSEMBLY (FIGURE 1).

2. REMOVE AND DISCARD VALVE UPPER MOUNT BOLT.

3. MODIFY LOAD VALVE LEVER BY CUTTING THE ARM ATTACHED TO THE VALVE 4" FROM THE END AS SHOWN IN FIGURE 2.

4. DRILL A 3/8" DIAMETER HOLE 2.570" FROM THE CENTER OF THE EXISTING ATTACHMENT HOLE AS SHOWN IN FIGURE 2.

5. INSTALL A 8MM X 1.25" X 3.0" FULL THREAD BOLT IN THE UPPER VALVE MOUNT BOLT HOLE.

6. INSTALL MODIFIED LEVER ARM TO VALVE SHAFT USING THE ORIGINAL HOLE AND INSERT THE THREADED BOLT IN THE NEW HOLE (FIGURE 3).

IMPORTANT: THE FLAT SURFACE ON THE SHAFT OF THE VALVE SHOULD BE VERTICAL AND FACING THE REAR OF THE VEHICLE WHEN THE MODIFIED LEVER ARM IS INSTALLED (FIGURE 4).

7. DOUBLE NUT THE THREADED BOLT WITH TWO SELF LOCKING NUTS AS SHOWN IN FIGURE 3.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY USE:

LABOR OPERATION: H0776

LABOR TIME: 0.3 HR.

FIGURES: 4

Object Number: 86819 Size: FS

Object Number: 87450 Size: FS

Object Number: 87905 Size: FS

Object Number: 86415 Size: FS

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.