GMC chervolet camaro 1999 Service Manual page 68

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General Information
This design causes one U-joint to cancel out the effect
of the other U-joint. The cancelled effects result in a
smooth, constant power flow from the output yoke
of the propeller shaft.
Second-order driveline vibrations occur when the
cancellation becomes unequal between the front
U-joint and the rear U-joint.
The main objective of this section is to correct the
conditions that interfere with the proper cancellation
effect of the U-joint. The most common condition,
especially where the launch shudder is concerned, is
incorrect driveline working angles (1,2). Other
factors may aggravate the condition.
Address the following factors before you attempt to
measure or correct the driveline working angles:
• Worn, failed, damaged or improperly installed
U-joint
• Worn, collapsed, or improper powertrain mounts
• Incorrect vehicle trim height adjustment for
the front suspension which aggravates the launch
shudder
• Incorrect trim height adjustment for the rear
suspension
• Trim height inspection includes trim heights that
are too low or too high.
On rear drive vehicles, the pinion nose tilts upward as
you lower the rear trim height.
If a second-order driveline vibration exists after you
correct these conditions, measure and correct
the driveline angles.
If the complaint is present only with cargo in the
vehicle, perform the measurements. with the vehicle
fully loaded. Once you correct a second-order driveline
vibration with the vehicle loaded, the vibration may
reappear with the vehicle unloaded. The reverse of this
condition is also true. You may have to reach a
compromise with the customer in this case.
Second-Order Driveline Vibration Symptoms
Second-Order driveline vibration has the following
signs and symptoms:
• The vibration is always related to vehicle speed.
• The vibration is usually torque-sensitive.
• The vibration is worse under a torque load.
Launch shudder is the most common complaint of a
second-order driveline vibration.
Launch shudder occurs during acceleration from
Q-40 km/h (0-25 mph). Launch shudder appears as a
low frequency shake, wobble, or shudder. The
driver may feel the vibrations in the seat or steering
wheel at low speeds of 0-24 km/h (0-15 mph).
The vibrations will increase in frequency as the vehicle
speed increases. Launch shudder feel~ more like
driveline roughness at higher speeds of 24-40 km/h
(15-25 mph). At speeds greater than 40 km/h (25 mph)
the vibration usually disappears.
Launch shudder vibration is equal to a second-order
vibration of the driveline. The EVA will not perceive
frequency information due to the transitory nature of
launch shudder.
Vibration Diagnosis and Correction 0-65
Driveline Working Angles
Tools Required
• J 38460 Digital Inclinometer
• J 23498-A Driveshaft Inclinometer
• J 23498 - 20 Driveshaft Inclinometer Adapter
6498
Driveline working angle does not refer to the angle of
any one shaft, but to the angle that is formed by
the intersection of two shafts.
The procedure for measuring and correcting driveline
working angles depends on whether the vehicle is
equipped with a propeller shaft consisting of one piece,
two pieces, or three pieces.
In order to verify the accuracy of the adapter, inspect
the angle of an accessible joint with the inclinometer
prior to assigning the adapter on an inaccessible joint.
One-Piece Propeller Shaft System
Raise the vehicle on a suitable hoist or on safety
stands. Ensure that the rear axle is supported at curb
height and that the wheels are free to spin. Refer
to Lifting and Jacking the Vehicle in General
Information. Place the transmission in NEUTRAL.
Ensure that the vehicle has a full tank of fuel or the
equivalent amount of weight in the rear to simulate a
full tank. The weight of 3.8 liters of gasoline
(1 gallon) is approximately 2.8 kg (6.2 lb).