DRIVELINE VIBRATION CAUSED BY BENT TRANSMISSION OUTPUT SHAFT. Chevrolet Chevy P RV/Van/Commercial Chassis 1995

SUBJECT: DRIVELINE VIBRATION CAUSED BY BENT TRANSMISSION OUTPUT SHAFT (REPLACE TRANSMISSION)

MODELS: 1992-95 CHEVROLET AND GMC TRUCK P3 MODELS WITH NV4500, 5 SPEED MANUAL TRANSMISSION (RPO'S MT8 + MW3) AND HYDRAULIC 4-WHEEL DISC BRAKES (RPO JF9)

********************************************************************** GM OF CANADA DEALERS REQUIRE GM ZONE OFFICE DISTRICT SERVICE MANAGER APPROVAL PRIOR TO REPLACEMENT OF MAJOR COMPONENTS LISTED IN THIS PRODUCT SERVICE BULLETIN. **********************************************************************

CONDITION:

DRIVELINE VIBRATION WHICH OCCURS AT THE SAME FREQUENCY AS THE 1ST ORDER OF DRIVELINE ROTATION AND INCREASES WITH VEHICLE SPEED. IF THE VIBRATION IS GREAT ENOUGH, IT CAN CRACK THE CLUTCH HOUSING.

CAUSE:

ONE CAUSE MAY BE A BENT TRANSMISSION OUTPUT SHAFT. THIS SHAFT CAN BE BENT BY APPLICATION OF THE PARK BRAKE WHILE THE VEHICLE IS IN MOTION. BRAKE APPLICATION CAN BE THE RESULT OF A MISADJUSTED PARK BRAKE OR USE OF THE PARK BRAKE AS A SERVICE BRAKE.

CORRECTION:

IF THE OUTPUT SHAFT IS FOUND TO HAVE MORE THAN .005" (.127 MM) OF RUN OUT, THE TRANSMISSION SHOULD BE REPLACED. THE REPLACEMENT TRANSMISSION LISTED BELOW HAS AN ADDITIONAL OUTPUT SHAFT SUPPORT BUSHING TO PREVENT OUTPUT SHAFT BENDING.

SERVICE PROCEDURE

DIAGNOSIS TIPS:

-THE VIBRATION WILL INCREASE WITH VEHICLE SPEED. -IF USING AN ELECTRONIC VIBRATION ANALYSIS TOOL (EVA), THE VIBRATION WILL BE EQUAL TO THE FIRST ORDER OF DRIVELINE ROTATION. IF IT IS NOT, THE VIBRATION IS NOT CAUSED BY A BENT TRANSMISSION OUTPUT SHAFT OR A DRIVELINE CONDITION. REFER TO THE APPROPRIATE SERVICE MANUAL SECTION 0C - VIBRATION DIAGNOSIS FOR FURTHER INFORMATION ON IDENTIFYING AND CORRECTING THE VIBRATION. -SIGNIFICANT VIBRATION CAN CAUSE A CRACKED CLUTCH HOUSING.

FOLLOW THE PROCEDURE BELOW TO DETERMINE IF THE VIBRATION IS CAUSED BY A BENT TRANSMISSION OUTPUT SHAFT OR SOME OTHER CONDITION. FOR DETAILED INSTRUCTION ON COMPONENT PART REMOVAL AND INSTALLATION REFER TO THE APPROPRIATE SERVICE MANUAL.

1. RAISE THE VEHICLE ON A HOIST AND REMOVE THE PROP SHAFT. 2. REMOVE THE YOKE/DRUM ASSEMBLY FROM THE TRANSMISSION OUTPUT SHAFT.

IMPORTANT: DO NOT REMOVE THE DRUM FROM THE YOKE. THESE PARTS ARE BALANCED AS AN ASSEMBLY AND SHOULD NOT BE DISASSEMBLED.

3. REMOVE THE PARK BRAKE ASSEMBLY FROM THE TRANSMISSION. 4. RE-INSTALL THE YOKE/DRUM ASSEMBLY PART WAY. LEAVE PART OF THE MACHINED SURFACE OF THE YOKE EXPOSED AND TAKE A DIAL INDICATOR READING OF OUTPUT SHAFT RUN OUT (FIGURES 1 AND 2). -IF THE RUN OUT EXCEEDS .005" (.127 MM) THE SHAFT IS BENT AND THE TRANSMISSION SHOULD BE REPLACED. IF IT DOES NOT, THE VIBRATION IS NOT CAUSED BY A BENT TRANSMISSION OUTPUT SHAFT. REFER TO THE APPROPRIATE SERVICE MANUAL SECTION 0C - VIBRATION DIAGNOSIS FOR FURTHER INFORMATION ON IDENTIFYING AND CORRECTING THE VIBRATION.

THE FOLLOWING PARTS SHOULD BE INSPECTED AND REPLACED AS NEEDED BEFORE INSTALLING A NEW TRANSMISSION: -CLUTCH HOUSING FOR CRACKS OR DAMAGE -CLUTCH DISC HUB AREA FOR CRACKS OR DAMAGE -PARK BRAKE SHOES FOR LUBE OIL CONTAMINATION.

THE FOLLOWING PARTS MUST BE REPLACED WHEN INSTALLING THE NEW TRANSMISSION: -CLUTCH PILOT BEARING. -SHIFT LEVER. -SHIFT KNOB (TRANSFER THE LOCKING NUT FROM THE OLD LEVER ASSEMBLY). -CLUTCH PIPE CLIP (NEW PART, DIESEL ONLY) (FIGURE 3).

IMPORTANT: INSPECT THE ORIGINAL PARK BRAKE DRUM/YOKE. IF THE PARK BRAKE DRUM IS CAST IRON, A NEW STEEL DRUM/YOKE ASSEMBLY IS REQUIRED.

PARK BRAKE ADJUSTMENT PROCEDURE:

1. ADJUST STAR WHEEL ON THE INSIDE OF BRAKE BY REMOVING THE PLUG ON THE WEB OF THE BACKING PLATE AND INSERTING AN ADJUSTING TOOL OR SCREWDRIVER. 2. ADJUST UNTIL DRUM DOES NOT TURN 3. BACK OFF ADJUSTMENT 2 TO 4 NOTCHES. 4. DRUM SHOULD TURN FREELY WITH A MAXIMUM OF LIGHT DRAG.

THE FOLLOWING FASTENER TIGHTENING SPECIFICATIONS SHOULD BE USED: -CLUTCH PRESSURE PLATE-TO-FLYWHEEL BOLTS 41 N.M (30 LBS. FT.) -CLUTCH HOUSING-TO-ENGINE BOLTS 39 N.M (29 LBS. FT.) -TRANSMISSION-TO-CLUTCH HOUSING BOLTS 100 N.M (74 LBS. FT.) -PARK BRAKE ASSEMBLY-TO-TRANSMISSION BOLTS 41 N.M (30 LBS. FT.) -YOKE-TO-OUTPUT SHAFT BOLT 87 N.M (65 LBS. FT.)

NOTICE: THIS TRANSMISSION REQUIRES A SPECIAL SYNTHETIC TRANSMISSION LUBRICANT. DO NOT SUBSTITUTE ANY OTHER LUBRICANT AS INTERNAL TRANSMISSION DAMAGE MAY RESULT. TRANSMISSION CAPACITY IS 3.78L (4 QUARTS). THE TRANSMISSION IS SHIPPED FROM GMSPO PRE-FILLED WITH FLUID. IF ADDITIONAL FLUID IS REQUIRED, A 1 QUART CONTAINER IS AVAILABLE AS P/N 12346190.

IMPORTANT: THIS TRANSMISSION HAS SLIGHTLY DIFFERENT GEAR RATIOS THAN THOSE BUILT BEFORE 2/17/94. TRANSMISSIONS BUILT BEFORE THIS DATE CAN BE IDENTIFIED BY A THREE DIGIT BROADCAST CODE. TRANSMISSIONS BUILT AFTER THIS DATE CAN BE IDENTIFIED BY A FOUR DIGIT BROADCAST CODE. A GEAR RATIO COMPARISON IS LISTED BELOW:

1ST 2ND 3RD 4TH 5TH REV OLD RATIO 6.34 3.44 1.71 1.00 0.73 6.34 NEW RATIO 5.61 3.04 1.67 1.00 0.75 5.61

THIS GEAR RATIO CHANGE ALSO AFFECTS PTO USAGE. PTO'S INSTALLED ON OLD RATIO TRANSMISSIONS CANNOT BE USED ON NEW RATIO TRANSMISSIONS.

PARTS INFORMATION

P/N DESCRIPTION QTY 15716115 TRANSMISSION ASSEMBLY 1 14061685 CLUTCH PILOT BEARING 1 15970951 SHIFT LEVER 1 15982540 SHIFT KNOB 1 15988085 CLUTCH PIPE CLIP (DIESEL ONLY) 1

THE FOLLOWING PART IS NEEDED ONLY IF THE ORIGINAL PARK BRAKE DRUM IS CAST IRON.

15704452 PARK BRAKE DRUM/YOKE 1

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OP DESCRIPTION LABOR TIME T2130 INSPECT FOR RUN OUT USING DIAL INDICATOR 0.8 HRS K2720 TRANSMISSION ASSEMBLY - REPLACE 2.8 HRS

FIGURES: 3

CAPTIONS: FIGURE 1 - MEASURING OUTPUT SHAFT RUN OUT FIGURE 2 - DRUM/YOKE ASSEMBLY, LOCATIONS FOR MEASURING RUN OUT FIGURE 3 - DIESEL CLUTCH PIPE CLIP

Object Number: 90433 Size: MF

Object Number: 88854 Size: MF

Object Number: 82718 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.