Classifying The Vibration - GMC Chevrolet Camaro 1998 Service Manual

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General Information
Additional Tests
You can perform one or more of the following tests for
unique vibration complaints such as those that are
torque/load sensitive, in addition to vehicle-speed or
engine-speed sensitive:
• Steering Input Test
• Standing Start Acceleration Test
Steering Input Test
This test is intended to determine how much the
wheel bearings and other suspension components
contribute to the vibration, especially those relating to
noises such as growl, grinding, and roaring.
Caution: Refer to Road Test Caution in Cautions
and Notices.
1. Drive through slow sweeping turns with the
vehicle at the vibration speed (mph) in one
direction, then in the other.
2. If the vibration gets worse or goes away, inspect
the following components as possible causes of
the vibration:
• The wheel bearings
• The hubs
• The tire tread
Standing Start Acceleration
{Launch Shudder) Test
The purpose of this test is to duplicate a vibration
called launch shudder. In some cases, a powertrain
mount or an exhaust ground-out may also be
suspected, depending on the symptoms.
Caution: Refer to Road Test Caution in Cautions
and Notices.
1 . Observe the necessary safety precautions.
2. With the vehicle at a complete stop and in gear,
remove your toot from the brake pedal.
3. Accelerate to 48-64 km/h (30-40 mph) while
looking tor vibrations that match the customer's
description.
Other possible causes of launch shudder include the
following conditions:
• Incorrect trim height. Refer to Trim Height
Specifications
• A worn or damaged drive axle CV joint.
• A ground-out engine/transmission mount.
• Faulty exhaust hangers and mounts.
Vibration Diagnosis and Correction 0-49
Classifying the Vibration
The next step after road testing the vehicle is to
identify the frequency of the duplicated and abnormal
vibration. Use the EVA in order to measure the
frequency. If the EVA is not available, the frequency
can be categorized into groups according to how
the vibration feels or sounds. The majority of vibrations
will fit into one of the following categories.
• Vibrations that can be felt:
- Shake
- Roughness
- Buzz
- Tingling
• Vibrations that make noise:
- Boom
- Moan and groan
- Howl
- Whine
Vibrations That Can Be Felt
Shake
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The shake is a low frequency vibration, typically
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5-20 Hz. The shake is sometimes seen in the steering
wheel, the seat, or the console. The best description
is the feeling from an out-of-round or unbalanced
tire. Customers may refer to shake in one of
the following terms:
• Shimmy
• Wobble
• Shudder
• Waddle
• Hop