Steering/Suspension - Interior Highway Speed Vibration
TECHNICALBulletin No.: 09-00-91-001B
Date: July 12, 2012
Subject: Shake/Vibration in Steering Wheel at Highway Speeds on Smooth Roads (Diagnose/Balance Tires/Wheels)
Models:
2008-2009 Cadillac CTS Sedan (RWD Only)
Excludes CTS-V, CTS-4 (AWD) Models
Supercede:
This bulletin is being revised to add a reference to GM approved tire force variation measurement equipment. Please discard Corporate Bulletin Number 09-00-91-001A (Section 00 - General Information).
Condition
Some customers may comment on shaking/vibration in the steering wheel while driving at highway speeds (typically between 105-121 km/h (65-75 mph) on smooth roads.
Correction
Use the following information to diagnose and correct the concern.
Notice
Do NOT align the vehicle or replace shocks for this condition. Adjusting wheel alignment or shock replacement will NOT correct a smooth road shake condition.
1. Road test the vehicle using the Electronic Vibration Analyzer (EVA) essential tool. Drive for a sufficient distance on a known, smooth road surface to duplicate the condition. Determine if the vehicle is sensitive to brake apply. If the brakes are applied lightly and the pulsation felt in the steering wheel increases, refer to the Brakes section of the service manual that deals with brake-induced pulsation.
If you can start to hear the vibration as a low boom noise (in addition to feeling it), but cannot see it, it likely has a first order (one pulse per propshaft revolution) driveline vibration. Driveline first order vibrations are high enough in frequency that most humans can start to hear them at highway speeds, but are too high to be able to be easily seen. These issues can be caused by driveline imbalance or misalignment. If the vehicle exhibits this low boom and the booming pulses in-and-out on a regular basis (like a throbbing), chances are good that the vehicle could have driveline vibration. This type of vibration is normally felt more in the "seat of the pants" than the steering wheel. There is a separate analysis for driveline vibrations. If this is the situation, refer to Corporate Bulletin Number 08-07-30-044D.
2. Next, record the Hertz (Hz) reading as displayed by the EVA onto the tire data 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. This reading confirms what the vehicle vibration frequency is prior to vehicle service and documents the amount of improvement occurring as the result of the various steps taken to repair. Completing the Steering Wheel Shake Worksheet below is required. A copy of the completed worksheet must be saved with the R.O. and a copy included with any parts returned to the Warranty Parts Center for analysis. A reading of 35 to 50 Hz indicates a first order propshaft vibration. If this is the situation, refer to Corporate Bulletin Number 08-07-30-044D. Generally, a reading of less than 20 Hz indicates a tire/wheel vibration and if this is the reading obtained, continue using this bulletin.
3. Visually inspect the tires and the wheels. Inspect for evidence of the following conditions and correct as necessary:
- Missing balance weights
- Bent rim flange
- Irregular tire wear
- Incomplete bead seating
- Tire irregularities (including pressure settings)
- Mud/ice build-up in wheel
- Stones in the tire tread
- Remove any aftermarket wheels and/or tires and restore vehicle to original condition prior to diagnosing a smooth road shake condition.
- Ensure the wheels are centered on the hub by loosening all wheel nuts and hand-tightening all nuts first by hand while shaking the wheel, then torque to specifications using a torque wrench, NOT a torque stick.
4. If corrections to any items in Step 3 were made, road test the vehicle to determine if the vehicle still exhibits the smooth road shake conditions.
If the smooth road shake/vibration still exists, continue below to diagnose wheel and tire concerns.
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
GM dealers may have various wheel balancers. If a road force measuring balancer 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.
- 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.
- 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 0.040. Readings of 0.030 inch or less are preferable for sensitive customers.
- 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
Warranty Information
For vehicles repaired under warranty, use:
Steering Wheel Shake Worksheet
When diagnosing vibration concerns, use the following worksheet in conjunction with the appropriate Vibration Analysis-Road testing procedure in the Vibration Correction sub-section in SI.
Refer to the appropriate section of SI for specifications and repair procedures that are related to the vibration concern.
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