HIGHWAY SPEED VIBRATION

REVISION: 06/25/96

THIS BULLETIN IS BEING REVISED TO ADD THE 1995-96 MODEL YEARS AND TO UPDATE THE "CORRECTION" INFORMATION. ARTWORK HAS ALSO BEEN ADDED. PLEASE DISCARD CORPORATE BULLETIN NUMBER 43-35-04 (SECTION 3 - STEERING/SUSPENSION). ********************************************************************

SUBJECT: HIGHWAY SPEED VIBRATION (CHECK TIRES, BRAKE DRUMS, FRAME MOUNTS, BALANCE, ADD FLOOR BRACE)

MODELS: 1994-96 BUICK CENTURY 1994-96 OLDSMOBILE CUTLASS CIERA

CONDITION:

SOME OWNERS MAY COMMENT THAT THE VEHICLE VIBRATES AT HIGHWAY SPEEDS (70-75 MPH) WITHOUT BRAKE APPLY.

CAUSE:

THE FOLLOWING IS A LIST OF POSSIBLE CAUSES FOR THIS VIBRATION. THEY ARE LISTED IN THE ORDER THAT THEY SHOULD BE ADDRESSED:

1. TIRE AND WHEEL IMBALANCE 2. BRAKE DRUM IMBALANCE 3. FLOOR PAN BRACE INSTALLATION 4. WHEELS 5. REAR HUBS 6. TIRES

CORRECTION:

TO CORRECT THIS CONDITION, THE FOLLOWING PROCEDURE SHOULD BE FOLLOWED:

1. TIRE/WHEEL ASSEMBLY: CHECK FOR PROPER BALANCE USING AN OFF-CAR DYNAMIC BALANCER. CORRECT IF REQUIRED.

2. BRAKE DRUMS: CHECK BALANCE ON BOTH BRAKE DRUMS WHILE THE REAR TIRES ARE OFF THE CAR.

A. MOUNT BRAKE DRUM ON A TIRE/WHEEL BALANCE MACHINE.

B. SET THE BALANCER TO THE STATIC MODE, 15" WHEEL DIAMETER, 3" RIM WIDTH, AND CORRECT DISTANCE TO THE INSIDE RIM FLANGE.

C. IF THE STATIC IMBALANCE IS GREATER THAN OR EQUAL TO 0.4 OZ., REPLACE THE DRUM(S), P/N 18020817.

3. FLOOR PAN BRACES:

A. FABRICATE 2 BRACES PER ATTACHED SKETCHES (FIGURES 1 AND 2).

B. PAINT BRACES FOR CORROSION PROTECTION.

C. REMOVE RIGHT FRONT AND BOTH REAR SHIELD BOLTS. DISCARD BOTH REAR SHIELD BOLTS.

D. TRIM REAR EXHAUST HEAT SHIELDS IN AREA OF BRACE MOUNTS AS REQUIRED TO EXPOSE OUTER TWO (2) HOLES IN "U" CHANNEL.

E. NOTCH LOWER RIGHT FRONT SHIELD FOR BRACE AS SHOWN.

F. INSTALL FRONT BRACE AS SHOWN IN FIGURE 3. LEAVE BOLTS LOOSE. USE 10 MM X 18 MM X 1.5 MM (3/8" X 3/4") BOLTS. YOU MUST USE A FLANGED HEX NUT TO PREVENT FALLING THROUGH THE SLOT. USE A FLAT WASHER UNDER EACH BOLT HEAD. REINSTALL RIGHT FRONT EXHAUST SHIELD BOLT LOOSELY.

G. INSTALL REAR BRACE AS SHOWN IN FIGURE 3. ALIGN BOTH BRACES AND THE EXHAUST SHIELDS. USE 8 MM X 18 MM X 1.25 MM (5/16" X 3/4") BOLTS. USE THE CORRESPONDING HEX NUTS ON THIS BRACE. FLANGED NUTS WILL NOT FIT. USE A FLAT WASHER UNDER EACH BOLT HEAD.

H. TIGHTEN ALL BRACE BOLTS AND USE GM GOODWRENCH #272 THREADLOCKER, P/N 12345382, OR EQUIVALENT, ON ALL THREADS.

NOTICE: ON 1996 MODELS ONLY - THE REAR 02 SENSOR WIRE IS ROUTED ON THE RIGHT UNDER THE EXHAUST SHIELDS. MAKE SURE THE WIRE IS NOT CUT WHEN TRIMMING THE SHIELDS AND THAT THE WIRE IS PROPERLY ROUTED WHEN FINISHED.

4. WHEELS: WHEEL RUNOUT (BOTH RADIAL AND LATERAL) SHOULD BE MEASURED PER THE PROCEDURE IN SERVICE MANUAL, SECTION 3E.

RUNOUT SPECIFICATIONS

STEEL WHEEL

RADIAL RUNOUT - 1.02 MM (0.040") LATERAL RUNOUT - 1.14 MM (0.045")

ALUMINUM WHEEL

RADIAL RUNOUT - 0.76 MM (0.030") LATERAL RUNOUT - 0.76 MM (0.030")

IMPORTANT: IT IS UNUSUAL TO FIND AN ALUMINUM WHEEL THAT HAS EXCESSIVE RUNOUT BECAUSE ALUMINUM WHEELS ARE MACHINED.

5. REAR HUB RUNOUT: ON A FEW VEHICLES, REAR HUBS HAVE BEEN FOUND WITH AN EXCESSIVE AMOUNT OF BOLT CIRCLE RUNOUT WHICH RESULTS IN A SECONDARY "DRONE" TYPE NOISE/VIBRATION COMING FROM THE REAR OF THE VEHICLE. TO CHECK FOR THIS, USE THE FOLLOWING PROCEDURE:

A. MOUNT WHEEL ON HUB AND MEASURE RADIAL RUNOUT.

B. REMOVE WHEEL AND ROTATE 2 STUD POSITIONS AND REMOUNT AND REMEASURE RUNOUT.

C. IF THE DIFFERENCE IN THE 2 RUNOUT READINGS IS GREATER THAN .23 MM (.009"), REPLACE THE HUB.

6. TIRE/WHEEL ASSEMBLY: CHECK THE TIRE/WHEEL ASSEMBLY FOR "FREE RADIAL RUNOUT". THE PROCEDURE FOR DOING THIS IS AS FOLLOWS:

A. MOUNT THE TIRE/WHEEL ASSEMBLY ON BALANCER.

B. WRAP TAPE AROUND THE CIRCUMFERENCE OF THE TIRE AT THE CENTER OF THE TREAD.

C. CHECK THE RADIAL RUNOUT ON THE TAPE WITH A DIAL INDICATOR. THE RADIAL RUNOUT SHOULD NOT EXCEED 12.7 MM (0.050") OR 15.0 MM (0.060") IF DONE ON THE VEHICLE.

EVALUATE VEHICLE FOR SPECIFIC VIBRATION AT 70-75 MPH.

IF VIBRATION IS STILL A CONCERN, REPLACE TIRES WITH MICHELIN XZ4 TIRES. IF A TIRE AND/OR WHEEL IS REPLACED, MAKE SURE IT IS BALANCED.

PARTS AVAILABILITY:

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OPERATION NUMBER DESCRIPTION LABOR TIME =============== =========== ==========

E0203 BALANCE 4 WHEELS USE PUBLISHED LABOR TIME

E0420 WHEEL REPLACE (1) USE PUBLISHED LABOR TIME

E0421 TIRE REPLACE (1) USE PUBLISHED LABOR TIME

E0201 BALANCE BRAKE DRUM (2) USE PUBLISHED LABOR TIME

A9300 FLOOR PAN REPAIR 0.6 HR (BRACE INSTALLATION)

FIGURES: 03 ATTACHMENTS: 00

FIGURE 1: FRONT BRACE MATERIAL: MILD STEEL

FIGURE 2: REAR BRACE MATERIAL: MILD STEEL

FIGURE 3: 2 BRACES INSTALLED LEGEND: 1. TRIM SHIELD TO EXPOSE BOLT HOLES IN CHANNEL - 2 PLACES. 2. THIS VIEW SEEN UNDER VEHICLE LOOKING FORWARD. 3. THIS VIEW SEEN LOOKING REARWARD AT FRONT BRACE. NOTCH METAL SHIELD FOR BRACE CLEARANCE.

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 1996 GENERAL MOTORS CORPORATION. ALL RIGHTS RESERVED.