G8 V6-3.6L (2008)
Correction
Correction
Road Testing
In order to provide the best diagnostic information, a road test with an EVA (Electronic Vibration Analyzer) or equivalent should be conducted.
Convenient locations for the magnetic transducer are the steering column, the driver front seat track and the trunk floor pan over the rear of the
propshaft. You should record your readings in each location between 50-70 mph (80-112 km/h). Each of the bold section headings above contain
additional information and diagnostic tips.
Important
Be sure tire pressure is set to the placard values.
The following sections offers possible vibration sources (in order of the least intrusive service procedure), how to identify them and the proper
corrections for each. The standardized GM Vibration Analysis Worksheet is included at the end of this bulletin to aid you in recording pertinent data.
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Road test the vehicle using the Electronic Vibration Analyzer (EVA) essential tool while driving 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 SI that deals with brake-induced pulsation.
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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 10 miles (16 km) at 45 mph (72 km/h) 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.
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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.
Wheel and Tire Assembly Balance & Road Force Variation
1. Visually inspect the tires and the wheels. Inspect for evidence of the following conditions and correct as necessary:
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Missing balance weights
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Bent rim flange
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Irregular tire wear
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Incomplete bead seating
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Tire irregularities (including pressure settings)
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Mud/ice build-up in wheel
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Stones in the tire tread
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Remove any aftermarket wheels and/or tires and restore vehicle to original condition prior to diagnosing a smooth road shake condition
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Ensure 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
2. If corrections to any items 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. 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 may 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. A guideline here is 18 lbs (8 kg)
or less (12 lbs (5 kg) or less are preferable for sensitive customers).
2. After confirming the wheel balance; install 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
