GMC Chevrolet Camaro 1998 Service Manual page 100

0-88 Vibration Diagnosis and Correction
95586
Vibration can also produce noise. As an example,
consider a vehicle that has an exhaust pipe
GROUNDED to the frame. The source of the vibration
is the engine firing impulses traveling through the
exhaust. The transfer path is a grounded or bound-up
exhaust hanger. The responder is the frame. The
floor panel vibrates, acting as a large speaker, which
produces noise. The best repair would be to
eliminate the transfer path. Aligning the exhaust
system and correcting the grounded condition at the
frame would eliminate the transfer path.
Basic Vibration Terminology
The following are the two primary components of
vibration diagnosis:
• The physical properties of objects
• The object's properties of conducting mechanical
energy
The repetitive up and down or back and forth
movement of a component cause most customer
vibration complaints. The following are the common
components that vibrate:
• The steering wheel
• The seat cushion
• The frame
• The 1/P
Vibration diagnosis involves the following simple
stepwise outline:
1 . Measure the repetitive motion and assign a value
to the measurement in cycles per second or
cycles per minute.
2. Relate the frequency back on terms of the
rotational speed of a component that is operating
at the same rate or speed.
3. Inspect and test the components for conditions
that cause vibration.
General Information
For example, performing the following steps will help
demonstrate the vibration theory:
95587
1. Clamp a yardstick to the edge of a table, leaving
about 50 cm (20 in) hanging over the edge of
the table.
2. Pull down on the edge of the stick and release
while observing the movement of the stick.
The motion of the stick occurs in repetitive cycles. The
cycle begins at midpoint, continues through the
lowest extreme of travel, then back past the midpoint,
through the upper extreme of travel, and back to
the midpoint where the cycle begins again.
The cycle occurs over and over again at the same
rate, or frequency. In this case, about 10 cycles in
one minute. If we measure the frequency to reflect
the number of complete cycles that the yardstick
made in one minute, the measure would be
10 cycles x 60 seconds= 600 cycles per minute (cpm).
We have also found a specific amount. of motion, or
amplitude, in the total travel of the yardstick from
the very top to the very bottom. Redo the experiment
as follows:
1 . Reclamp the yardstick to the edge of a table,
leaving about 25 cm (1 O in) hanging over the
edge of the table.
2. Pull down on the edge of the stick and release
while observing the movement of the stick.
The stick vibrates at a much faster frequency:
30 cycles per second (1800 cycles per minute).
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