In-Shop Test & Repair Procedures
IN-SHOP TEST PROCEDURES
A road test is recommended, however, in-shop testing can be performed if road conditions prevent road testing. The following is recommended for in-shop testing:
1. Check the tire pressures and adjust according to tire placard or operator's manual.
2. Check front end alignment and adjust as required.
3. Raise vehicle by #1 crossmember until front wheels are off of floor. Place safety stands under right and left side near the tie-down brackets. Lower the vehicle onto the jack stands.
CAUTION: FOR SAFETY, APPLY PARKING BRAKE FIRMLY AND BLOCK REAR WHEELS.
5. Start the engine and run the front wheels up to the speed of the steering wheel shimmy, as indicated in the Diagnosis section of this bulletin. Verify the steering wheel shimmy and note the severity.
CAUTION: WHEN IN-SHOP TESTING IS CONTINUED FOR A LONG PERIOD OF TIME, BOTH FRONT WHEELS MAY NOT ROTATE AT THE SAME SPEED DUE TO RISING TEMPERATURES OF THE DIFFERENTIAL GEAR LUBRICANT. IF THIS OCCURS, STOP THE TESTING UNTIL THE LUBRICANT COOLS.
REPAIR PROCEDURES
I. Procedures When Using "On Car Type Wheel & Tire Balancer"
A. Check radial and lateral runout of tires and wheels. Also check tires for tread or sidewall damage. Refer to appropriate service manual for runout specifications.
If runout is excessive, rotate the out-of-spec tire and wheel to the rear.
Check tire pressure and runout on the tire (s) moved to the front. Match mounting of the tires may be necessary to bring the runout into specifications.
NOTE: THE WHEELS SHOULD ALWAYS BE TORQUED TO SPECIFICATIONS USING A HAND OPERATED TORQUE WRENCH. DO NOT USE AN IMPACT WRENCH.
B. Balance the front tire and wheel assemblies using the "on-car balancer."
It is recommended that balance be within 1/4 oz. or 10g.
C. Verify the condition by running the vehicle using the procedures listed under "In-Shop Test Procedures."
II. Procedures When Using "Off-Car
Type Wheel & Tire Balancer"
Procedures for "on-car balancing" are recommended since steering shimmy is due to the total of all imbalance conditions of the rotating components such as tires, wheels, hubs, and disc rotors. The following car balancing can be performed when "on-car balancing" equipment is not available.
A. Check radial and lateral runout of tires and wheels. Also check tires for tread or sidewall damage. Refer to appropriate service manual for runout specifications.
B. If runout is excessive, rotate the out-of-spec tire and wheel to rear. Check tire pressures and runout on the tire(s) and wheel(s) removed from the rear.
Match mounting may be necessary to bring the tire runout into specifications.
NOTE: THE WHEELS SHOULD ALWAYS BE TORQUED TO SPECIFICATION USING A HAND OPERATED TORQUE WRENCH. DO NOT USE AN IMPACT WRENCH.
C. Balance the tire and wheel assemblies to within 1/4 oz. or 10g.
Computer-type balancing equipment is required and the wheels must be piloted on the balancer using a lug mount-type adapter.
D. Verify the condition by running the vehicle as described in the "In-Shop Test Procedures" or road test.
NOTE: IT MAY BE NECESSARY TO FINE TUNE THE BALANCE OF THE WHEEL AND TIRE ASSEMBLIES AFTER THEY ARE REINSTALLED ON THE VEHICLE. THIS MAY BE NECESSARY DUE TO MINOR IMBALANCE OF OTHER ROTATING COMPONENTS.
III. The following repair should be performed if the vehicle
continues to exhibit the steering wheel shimmy after the balancing operations have been performed.
Parts Required: 4 - Strut Bar Bushings PN MB349027
FIGURE 2:
New strut bar bushings have been designed "stiffer" to reduce strut bar and lower control arm movement. The softer (original) bushings may not dampen road/tire inputs sufficiently.
A. Obtain four (4) new style strut bar bushings.
B. Replace strut bar bushings with new style. Be sure the largest end of the bushings are installed against the strut bar bracket (Figure 2). Refer to appropriate service manual for detailed procedures.
C. Check front wheel alignment adjust as required.
D. Verify that the condition has been corrected by road testing the vehicle.
IV. The above listed repair procedures should eliminate the
steering wheel oscillation (shimmy) condition. In the event the condition is not corrected to the customer's satisfaction, contact the Zone representative for assistance.
POLICY: Reimbursable within the provisions of the warranty
PASSENGER CAR LABOR OPERATION TIME SCHEDULE:
TIME ALLOWANCE: Refer to Labor Operation Time Schedule for all operations except front end alignment.
If front end alignment is required as a result of this bulletin procedure, use the following labor operation number:
Labor Operation No. 02-00-01-90 . . . . . . . . . . 0.8 Hrs.
FAILURE CODE: 2X - Vibration or Chatter