GMC Chevrolet Camaro 1998 Service Manual page 62

0·50 Vibration Diagnosis and Correction
In most cases, damage to or wear of the following
components is to blame for the shake:
• The tires
• The wheels
• The brake rotors (vehicle-speed sensitive)
• The steering tie rod ends
• Tt,e suspension ball joints
• The engine (engine-speed sensitive)
Roughness
Roughness is a vibration with a slightly higher
frequency than the shake, usually 20-50 Hz.
Roughness is similar to the feeling you get from
holding a jigsaw.
/ Buzz
Buzz is slightly higher in frequency:
50-100
Hz. A
buzz is similar to the feel of an electric razor. You may
feel it in your hands through the steering wheel, in
the feet through the floor, or in the seat. Inspect the
following components for a possible cause:
• The exhaust system
• The A/C compressor
• The engine
Tingling
This is the highest frequency that can still be felt.
Tingling may sometimes produce a PINS AND
NEEDLES sensation. Customers may say the vibration
puts their hands or feet TO SLEEP.
Vibrations That Make Noise
Boom
Boom is a low frequency interior noise of 20-60 Hz.
Sometimes the customer complains of a 'pressure
in their ears. Examples of similar noises include
a bowling ball rolling down an alley, deep thunder, or
a bass drum.
A customer may use the following words to
describe boom:
• Droning
• Growling
• Moaning
• Roaring
• Rumbling
• Humming
Boom may not be accompanied by a perceptible
vibration (roughness).
General Information
Moan or Drone
Moan or drone is a sustained tone at a low frequency
of 60-120 Hz, somewhat higher than boom.
Examples of similar noises include a bumble bee, or
blowing air across the top of a soda bottle. Examples
of words to describe moan or drone are humming,
buzzing, resonance. Moan or drone may be
accompanied by a perceptible buzzing vibration.
Inspect the following systems:
• The powertrain mounts
• The exhaust system.
Howl
Howl isp noise at mid-range frequency of
120-300 Hz. This sounds like the wind howling.
Whine
Whine is a prolonged, high-pitched sound in the
300-500 Hz range, and is usually related to the
meshing gears or gear noise. Similar sounds include
mosquitoes, turbine engines, and vacuum cleaners.
Matching Frequency to Component Speed
At this point in the diagnosis, the vibration has been
duplicated, designated as abnormal, identified as being
related to engine speed or vehicle speed, an.d
assigned a frequency from the EVA or categorized
into a symptom group based on how it feels or sounds.
Automotive vibrations are usually related to the
rotating speed of a coniponent. The speed of these
components wjll be calculated using either an
engine speed or vehicle speed method. The engine
rpm readings taken (;iuring the road test will be used in
diagnosing vibrations that are engine speed sensitive.
If the vibration is vehicle speed sensitive, the
rotational speed of the tires needs to be determined.
As long as the vehicle is operated at a constant speed,
the tires will operate at a constant speed. These
speed is measured in rotations or cycles per second.
The reading is then compared to the frequency of
the vibration, which is also measured in cycles
per second.
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