CTS RWD V6-3.6L (2008)
Tire and Wheel Diagnosis
1. Set the tire pressure to the placard values.
2. Road test the vehicle with the Electronic Vibration Analyzer (EVA) essential tool for a sufficient distance on a known, smooth road surface to
duplicate the condition. Record the Hertz (Hz) reading as displayed by the EVA onto the Steering Shake Worksheet found at the end of this
bulletin. This should be done after a tire break-in period of at least 16 km (10 mi) at 72 km/h (45 mph) or greater, in order to eliminate any
possible tire flat-spotting. Generally, a reading of less than 20 Hz indicates a tire/wheel vibration.
3. If flat-spotting is the cause, provide the explanation that this has occurred due to the vehicle being parked for long periods of time and that the
nature of the tire is to take a set. Refer to Corporate Bulletin Number 03-03-10-007E: Information on Tire/Wheel Characteristics (Vibration,
Balance, Shake, Flat Spotting) of GM Original Equipment Tires.
4. If the road test indicates a shake/vibration exists, check the imbalance of each tire/wheel assembly on a known, calibrated, off-car dynamic
balancer. If any assembly calls for more than 1/4 ounce on either rim flange, remove all balance weights and rebalance to as close to zero as
possible. If you can see the vibration (along with feeling it) in the steering wheel (driving straight without your hands on the wheel), it is very
likely to be a tire/wheel first order (one pulse per revolution) disturbance. First order disturbances can be caused by imbalance as well as
non-uniformities in tires, wheels or hubs. This first order frequency is too low for a human to hear, but if the amplitude is high enough, it can be
seen.
Important
Some GM dealers may have a Hunter GSP9700 Road Force Balancer or a Coats XR1850 Runout Balancer. If a Hunter GSP9700
machine is available, it may also be used to measure the radial force variation of the tire/wheel assembly. Refer to first bulleted item
under #1 in the next section.
5. After confirming the wheel balance, install the wheel and tire assembly on the vehicle per service procedures with the specified tightening process.
If any changes were made, road test the vehicle again.
If the smooth road shake/vibration still exists, continue below to measure wheel runout and assembly radial force variation.
Measuring Wheel Runout and Assembly Radial Force Variation
Important
The completed worksheet at the end of this bulletin must be attached to the hard copy of the repair order.
1. Measure radial force variation and radial runout.
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If a road force/balancing machine is used, record the radial force variation (RFV) on the worksheet at the end of this bulletin. If one or more of
the tire/wheel assemblies reads more than 18 lbs, match mount the tire to the wheel to get below 18 lbs. Readings of 12 lbs or less are
preferable for sensitive customers. If the machine is not available and the EVA data suggests there is an issue, swap the tire and wheel
assemblies from the front to the back, including the lowest RFV assembly to the front left corner. Re-check on the EVA and if the problem still
exists, test another vehicle to find tires that do not exhibit the same frequency and swap those tires onto the subject vehicle.
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If a runout/balancing machine is used, record the radial runout of the tire/wheel assemblies on the worksheet at the end of this bulletin. If one
or more of the tire/wheel assemblies are more than.040, match mount the tire to the wheel to get below.040. Readings of.030 inch or less are
preferable for sensitive customers.
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If the RFV or runout cannot be reduced to an acceptable level, replace the affected tire(s) under the guidelines of the GM Tire Warranty.
2. Place tires with lowest RFV on the front of the vehicle.
3. Road test the vehicle to determine if the shake/vibration has been eliminated.
If the smooth road shake/vibration still exists, continue below with additional possible corrections.
Additional Possible Corrections
1. Measure the radial runout of the brake rotors to determine if one (or more) have elevated runout measurements. If the lateral run out (LRO)
measurement is 0.050 mm (0.002 in) or LESS, no correction is necessary. If this measurement is greater, refer to Corporate Bulletin Number
00-05-22-002L (Disc Brake Warranty Service and Procedures) for additional information on correcting rotor runout conditions.
2. If all other service options have been exhausted and no solution has been acceptable, revised front lower control arms are available for this vehicle.
The replacement front lower control arm assemblies contain tuned bushings which desensitize the steering to slight vibrations. Refer to Front
Lower Control Arm replacement procedures in SI.
After this repair is completed, road test the vehicle to assure the vibration has been eliminated.
Notice
Replacement front control arms should NOT be installed unless all other corrective actions have been exhausted, objectionable levels of vibration
still exist AND the worksheet below is completed.
3. Additional information on vibration correction is available by contacting GM Technical Assistance if additional measures are required.
Parts Information
