GMC Chevrolet Camaro 1998 Service Manual page 80

0-68 Vibration Diagnosis and Correction
Correcting On-Vehicle Imbalance
On-vehicle imbalance may result from components
other than the tire and wheel assemblies having
imbalance. An on-vehicle high-speed balance or
replacement of suspected components may be
necessary in order to correct the condition.
Rotors do not have a set tolerance. However, rotors
with more than 0.75 ounce imbalance have the
potential to cause vibration. The rotors can be
inspected for imbalance using either the on-vehicle or
the off-vehicle method as described below:
Checking Rotor Imbalance (On-Vehicle)
1. Support the vehicle rear axle on a suitable hoist.
Refer to Lifting and Jacking the Vehicle
2.
Remove the rear tire and wheel assemblies. Refer
to Wheel Removal
3. Reinstall the wheel nuts in order to retain the
rotors.
Caution: Refer to Work Stall Test Caution in
Cautions and Notlces.
4. Take the necessary precautions.
5. Run the vehicle at the complaint speed while
inspecting for vibration.
6. If the vibration still exists, perform the
following steps:
6.1 . Remove the rotors.
6.2. Run the vehicle back to speed.
7. If the vibration is eliminated, perform the
following steps:
7.1. Remove the rotors one at a time.
7.2. Perform the vibration test for each rotor.
7.3. Replace the rotor causing the imbalance.
7.4. Inspect the balance of the new rotor.
Checking Rotor Imbalance (Off-Vehicle)
1 . Measure the diameter and the width of the rotor.
2. Mount the rotor on a balancer in the same
manner as a wheel.
Important: The rotors can only be inspected for static
imbalance. Ignore the dynamic imbalance reading.
3. Inspect for static imbalance.
On-Vehicle Balancing Procedure
The vibration problem may not be correctable with the
components removed from the vehicle. An on-vehicle
high-speed balancer may be required in order to
balance the tire and wheel assemblies while
still mounted on the vehicle. On-vehicle balancing will
balance the hubs and the rotors simultaneously,
and will compensate for any residual runout
encountered as a result of mounting the tire and
wheel assemblies on the vehicle as opposed
to off-vehicle balancing.
General Information
Follow the on-vehicle balancer manufacturer operator's
manual for specific instructions while keeping the
following tips in mind:
Balancing Tips
• Do not remove the off-vehicle balancing weights.
The purpose of on-vehicle balance is to FINE
TUNE the assembly balance already achieved, not
to start over again.
• If the on-vehicle balance calls for more
than 1 ounce of additional weight, split the weight
between the inboard and outboard flanges of
the wheel, so as not to upset the dynamic balance
of the assembly that was achieved in the
off-vehicle balance.
• An EV A vibration sensor placed on the fender of
the vehicle during the on-vehicle balance is an
excellent indicator of the amplitude of the vibration,
and the effect that the balance has on the
vibration.
• Evaluate the vibration after the on-vehicle balance
in order to determine if the vibration condition has
been resolved.
Radial Force Variation
1
176971
Radial force variation is the difference in the stiffness
of a tire as the tire rotates and contacts the road.
The tire and wheel assemblies have some variation
due to splices in the tire plies. These splices do
not cause a problem unless the force variation is
excessive. These STIFF SPOTS in the tire (1)
can deflect the tire and wheel assembly upward as the
assembly contacts the road.
If the tire has only one stiff spot, the spot will deflect
the spindle once per each revolution of the tire
and wheel assembly, thus causing a first-order
tire/wheel vibration. If the tire has two stiff spots, the
spots cause a second-order vibration. First- and
second-order tire/wheel vibrations are the most
common to occur as a result of radial force variation.
Third-, fourth-, or higher orders are possible but
rarely occur.