GMC chervolet camaro 1999 Service Manual page 67

0-64 Vibration Diagnosis and Correction
Anything that effects the pinion gear and how the
pinion gear contacts the rotating ring gear may
contribute to a first-order, torque-sensitive driveline
vibration. The only way to correct the condition
is to replace the faulty components. In most cases,
you must replace the ring and pinion gear set and the
related bearings. In some cases, you must replace
the axle housing. Complete a close-up visual
inspection for damage or unusual wear in order to
measure or identify the specific faulty component.
It is possible to isolate an internal axle vibration. Install
a known good axle assembly from a stock unit.
Verify that the known good axle assembly does not
have a vibration problem.
Once you correct the internal axle problem, road test
the vehicle. Inspect the vehicle for vibration.
Balance the driveline, as necessary, in order to
eliminate any remaining vibration.
Diagnosing Second-Order Driveline
Vibration
Second-Order Driveline Vibration Theory
182178
A faulty universal joint (U-joint) may cause a vibration
that occurs twice for each rotation of the propeller
shaft. This type of vibration is called a second-order
vibration. ·
Second-order driveline vibrations are independent of
runout or balance of a driveline component.
The following description of basic U-joint theory will
help you to understand where second-order driveline
vibrations originate and why they occur.
• As the propeller shaft rotates, the U-joint speeds
up and slows down twice for each rotation of
the propeller shaft.
• The acceleration and deceleration of the U-joint is
not visible. If there is vibration in the U-joint, the
acceleration and deceleration will be audible
and tactile.
General Information
• Compare the U-joint in a vehicle to a universal-type
socket. When a universal-type socket is used to
tighten a bolt, the socket will bind and release as (
the socket turns toward 90 degrees. The bind and
release occurs twice for each revolution of the
socket,
• The U-joint in a vehicle works in the same way as
the universal-type socket. The bind and release
effect is directly proportional to the angle that the
U-joint operates: the greater the angle, the greater
the effect.
• Because the transmission output speed is constant,
the binding and releasing of the U-joint is better
described as an acceleration and deceleration
which occurs twice for each revolution of the
propeller shaft.
• If the propeller shaft is running slowly, the
accelerating and decelerating effect is visible. The
acceleration and deceleration may create a
vibration due to the fluctuations in force that are
generated at high speeds.
Canceled Out Driveline Angles
Legend
(1) Front Working Angle
(2) Rear Working Angle
182180
Engineers design drivelines in order to compensate for
the accelerations and decelerations in order to
produce a smooth, constant flow of power, as
listed below:
• The transmission drives the front yoke of the
propeller shaft at a smooth and constant speed.
• The first U-joint causes the power to fluctuate
twice for each revolution of the propeller shaft.
• The second U-joint, oriented 90 degrees from the
first U-joint, causes the power to fluctuate
opposite that of the first U-joint.
• As the first U-joint slows down, the second U-joint
speeds up.
(