LAUNCH SHUDDER AT 0-15 MPH (REPHASING PROPELLER SHAFT). GMC Truck GMC Suburban

REVISION 09/27/93

SUBJECT: LAUNCH SHUDDER (INSTALL ADDITIONAL MOUNT)

THIS BULLETIN IS BEING REVISED TO ADD THE 1993 MODEL YEAR, ADD K2 TRUCKS, AND CHANGE THE CORRECTION, SERVICE PROCEDURE AND WARRANTY INFORMATION SECTIONS. PLEASE DISCARD PREVIOUS DIVISIONAL PUBLICATIONS:

DIV BULLETIN # PUBLISH DATE

GMC TRUCK 92-4A-38 JANUARY 1992 CHEVROLET 92-72-6A JANUARY 1992 GM OF CANADA 92-4-101 MARCH 1992 ---------------------------------------------------------------------

MODELS: 1988-93 K1,2 EXTENDED CAB WITH 8 FOOT BOX (MODELS K10953, K20953)

CONDITION:

SOME OWNERS MAY COMMENT THAT THEIR VEHICLE EXPERIENCES A LAUNCH SHUDDER CONDITION. THIS CONDITION USUALLY OCCURS FROM 0 THROUGH ABOUT 10 MPH AND IS USUALLY MORE NOTICEABLE DURING HARD ACCELERATION, WHEN THE VEHICLE IS HEAVILY LOADED OR WHEN TOWING.

CAUSE:

THIS CONDITION IS CAUSED BY THE PROPELLER SHAFT U-JOINTS WORKING AT HIGH TORQUE AND ANGLE UNDER ACCELERATION AND RESULTS IN A SHUDDER OR VIBRATION.

CORRECTION:

THIS CONDITION MAY BE CORRECTED BY INSTALLING A MOUNT BETWEEN THE TRANSFER CASE EXTENSION AND THE TORSION BAR SUPPORT CROSSMEMBER.

SERVICE PROCEDURE: (FIGURE 1)

1.RAISE VEHICLE ON HOIST. 2.INSTALL THE RUBBER INSULATOR AROUND THE TRANSFER CASE EXTENSION AND SLIDE THE RETAINER OVER THE RUBBER INSULATOR. 3.LOOSELY BOLT THE RETAINER TO THE BRACKET. THE RETAINER SHOULD BE BOLTED TO THE FORWARD BRACKET HOLES FOR A 4L60 OR 4L60-E TRANSMISSION AND THE REARWARD BRACKET HOLES FOR A 3L80 OR 4L80-E TRANSMISSION. 4.MARK THE LEFT-TO-RIGHT HOLE LOCATIONS BY ALIGNING THE BRACKET FLAT AGAINST THE REAR SIDE AND PARALLEL WITH THE BOTTOM EDGE OF THE TORSION BAR SUPPORT CROSSMEMBER. 5.DRILL A 13MM (1/2") HOLE THROUGH BOTH LOCATIONS AND BOTH FACES OF THE TORSION BAR SUPPORT CROSSMEMBER.

IMPORTANT: THE HOLES THROUGH THE TORSION BAR SUPPORT CROSSMEMBER MUST BE PARALLEL AND EQUALLY SPACED THROUGH BOTH FACES. IF THEY AREN'T, IT MAY BE DIFFICULT TO INSTALL THE SPACER.

6.PLACE THE SPACER INSIDE THE TORSION BAR CROSSMEMBER, ALIGN THE FASTENER HOLES (TWO PLACES) AND INSERT TWO BOLTS THROUGH FROM THE FRONT OF THE TORSION BAR CROSSMEMBER. 7.INSTALL THE BRACKET TO THE TORSION BAR SUPPORT CROSSMEMBER USING THE TWO INSTALLED BOLTS. ALIGN THE BRACKET PARALLEL WITH THE CROSSMEMBER AND INSTALL THE WASHERS AND NUTS. TORQUE THE BRACKET-TO-CROSSMEMBER FASTENERS TO 70 N.M (52 LBS. FT.). 8.TORQUE THE RETAINER-TO-BRACKET FASTENERS TO 45 N.M (33 LBS. FT.).

IMPORTANT: BE SURE THE METAL RETAINER AND BRACKET DO NOT TOUCH THE TRANSFER CASE. METAL-TO-METAL CONTACT WILL CREATE A GROUND-OUT CONDITION AND MAY CAUSE NOISE OR VIBRATION.

SERVICE PARTS INFORMATION

P/N DESCRIPTION QTY

15963562 RETAINER 1 15963563 INSULATOR 1 11508897 BOLT (RTNR-BRKT) 2 15974622 BRACKET 1 11515781 BOLT (BRKT-SUPT) 2 15650964 WASHER (BRKT-SUPT) 2 11515750 NUT (BRKT-SUPT) 2 15958234 SPACER 1

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OP LABOR TIME T7356 0.4 HRS

FIGURES: 1

Object Number: 85234 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.