GMC chervolet camaro 1999 Service Manual page 56

General Information
For example, if the complaint speed is 60 mph, the
number of increments is 12. According to the following
table, a tire with size of P235/75R15 has a value of
1.00 Hz. You can calculate the rotational speed
at 60 mph:
12 increments x 1 Hz
=
12 Hz
Tire/Speed
Revs/Sec (Hz)
Tire Size Tread at 5 MPH
P235/55R16 AL2 1.11
P215/60R16 AL2 1.10
P275/40ZR17 HW4 1.12
P245/50ZR16 AL3 1.13
P215/60R16 AL3
1.10
P245/50ZR16 HW4 1.13
Tread Types: AL2: Touring AL3: Export HW4:
Performance Tire
Sometimes, the tire/wheel vibration may be of a
higher-order. In order to compute possible higher-order
vibrations, multiply the rotational speed of the tires,
in Hertz, at the complaint speed by the order number.
If any of these matches the vibration frequency, a
vibration of that particular order is present in one of the
tire/wheel assemblies.
Steering and Suspension Assembly Vibrations
Steering and suspension assembly vibrations are
the first level of testing for low-frequency vibrations that
are sensitive to vehicle speed. The symptoms of a
steering/suspension first-order vibration are a shimmy
or a shake. This is usually felt in the steering wheel
or in the seat. Inspect the following components
for wear or damage:
• The steering tie rod ends
• The suspension ball joints
Calculating Propeller Shaft Rotation
The propeller shaft drives the tires through the rear
axle. Knowing the rotational speed of the tires enables
you to easily calculate the speed of the propeller
shaft. Therefore, you can determine the rotational
speed of the propeller shaft by multiplying the
rotational speed of the tires by the ratio of the
rear axle.
Matching Frequency to Component RPM
RPO Description Ratio
GU2 Ratio, Rear Axle 2.73
GU4 Ratio, Rear Axle 3.08
GU5
Ratio, Rear Axle 3.23
GU6 Ratio, Rear Axle 3.42
Vibration Diagnosis and Correction 0-53
1. Obtain the tire speed by performing the tire speed
calculation, described earlier in this section.
2. Determine the axle ratio using one of the following
methods:
• Cross reference the axle information from the
service information part label to the parts book.
• Cross reference the axle identification
code that is stamped on the axle to the
parts book.
• Perform the following calculation:
2.1. Make a mark on the tires and the
propeller shaft.
2.2. Rotate the tires for one complete
revolution, counting the number of
propeller shaft rotations.
For example, the propeller shaft
rotates approximately 3112 times for
every tire revolution. The axle
ratio is 3.5:1
3. In order to find the propeller shaft rotation speed,
multiply the tire speed by the rear axle ratio.
In the earlier example, at a 60 mph complaint speed:
12 Hz x 3.5 = 42 Hz
Match the frequency of the vibration from the EV A
with the rotational speed of a component {either a tire
_ or a wheel). If none of the frequencies match, do
one of the following actions:
• Recheck the data.
• Attempt to match the figures again, allowing for
1-5 mph of speedometer error.
When you have matched the speed of the component
with the frequency of the vibration, refer to the
service information that outlines the repair procedures
for that particular component.
Rotor/Drum Imbalance
Rotors and drums do not have a set tolerance.
However, rotors or drums with more than
21 g {0.75 ounce) imbalance have the potential to
cause vibration. Inspect the rotors and the drums for
imbalance using either the on-vehicle or the off-vehicle
method.
Checking Rotor/Drum Imbalance (On-Vehicle)
1. Raise and suitably support the vehicle. Refer
to Lifting and Jacking the Vehicle in General
Information.
2. Remove the rear tire and wheel. Refer to Tire and
Wheel Removal and Installation (Wheel Removal)
in Tires and Wheels.
Caution: Refer to Work Stall Test Caution in
Cautions and Notices.
3. Reinstall the wheel nuts in order to retain the
rotors/drums.
4. Run the vehicle at the complaint speed while
inspecting for the vibration.