Driveline Working Angles Adjustment: Notes

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Rear axle wind-up may cause launch shudder even when all of the working angles are within specifications. Rear axle wind-up occurs when heavy torque during acceleration causes the pinion nose to point upward. In order to compensate for axle wind-up, tip the pinion nose downward. Install the axle shims incrementally, performing a road test after each shim. Add shims until the road test indicates that the shudder is eliminated.

Wedge shims of different sizes are available through the parts' system and independent suppliers for the purpose of shimming the rear axle angle. Wedge shims are available in 2, 3, and 4 degrees.

CAUTION: Never attempt to shim a rear axle using anything except shims that are designed for this purpose. Failure to do so will result in the shims falling out and a loss of vehicle control and that could cause personal injury.

Fig 1: Installing Shims Between Leaf Spring And Spring Seat

Courtesy of GENERAL MOTORS CORP.

Choose a wedge shim based on the Measuring Propeller Shaft Angle Procedure.
Remove the U-bolt. Refer to Leaf Spring Replacement in Rear Suspension.
Install the shims (5) in order to increase or decrease the angle of the rear axle pinion. Install the shims between the leaf spring (3) and the spring seat (2).
Important

After installing the shims, ensure that the U-bolt has 2 or 3 threads above the nut. Ensure also that the center bolt, located in the spring seat, is long enough to seat in the locator hole. If these 2 conditions do not exist, use longer U-bolts and center bolts. Longer U-bolts and center bolts are available through local spring shops.
Install the U-bolt. Refer to Leaf Spring Replacement in Rear Suspension.