Vibrations That Make Noise; Matching Frequency To Component Rpm - GMC chevrolet camaro 2000 Service Manual

0:-48 Vibration Diagnosis and Correction
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
your 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 vibration frequency that you can
feel. Tingling may sometimes produce a pins and
needles sensation. Customers may say the vibration
creates numbness in their hands or feet.
Vibrations That Make Noise
Boom
Boom is a low frequency interior noise of 20-60 Hz.
Sometimes the customers complain 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
e
Rumbling
O
Humming
Boom may be accompanied by a perceptible vibration
(roughness).
Moan or Drone
Moan or dron'e 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. A customer
may use the following words to describe moan
or drone:
" Humming
e
Buzzing
" Resonance
Moan or drone may be accompanied by a perceptible
buzzing vibration. Inspect the following systems:
" The powertrain mounts
., The exhaust system
General Information
Howl
Howl is a noise at mid-range frequency of
120-300 Hz. This so.unds like the wind howling.
Whine
Whine is a prolonged, high-pitched sound in the
300-500 Hz range. Whine is usually related to the
meshing gears or gear noise. Similar sounds include
mosquitoes, turbine engines, and vacuum cleaners.
Matching Frequency to Component RPM
At this point in the diagnosis, the vibration has
gone through the following analysis:
• The vibration has been duplicated.
• The vibration has been designated as abnormal.
• The vibration has been related either to engine
speed or to vehicle speed.
• The vibration has been assigned a frequency from
the EV A or identified based on its feel or its sound.
Automotive vibrations are usually related to the rotating
speed of a component. Calculate the speed of these
components using either an engine speed method or a
vehicle speed method. Use the engine RPM readings
taken during the road test in order to diagnose the
vibrations that are sensitive to engine speed.
If the vibration is sensitive to vehicle speed, determine
I
the rotational speed of the tires. As long as you \
operate the vehicle at a constant speed, the tires will
operate at a constant speed. This 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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