Analysis of Vibration

WARNING: A VEHICLE EQUIPPED WITH A TRACTION-LOK DIFFERENTIAL WILL ALWAYS HAVE BOTH WHEELS DRIVING. IF ONLY ONE WHEEL IS RAISED OFF THE FLOOR AND THE REAR AXLE IS DRIVEN BY THE ENGINE, THE WHEEL ON THE FLOOR COULD DRIVE THE VEHICLE OFF THE STAND OR JACK. BE SURE BOTH REAR WHEELS ARE OFF THE FLOOR.

Few vibration conditions are caused by the rear axle. On a vibration concern, follow the diagnosis procedure unless there is a good reason to suspect the axle.

TIRES

WARNING: DO NOT BALANCE THE WHEELS AND TIRES WHILE THEY ARE MOUNTED ON THE VEHICLE. POSSIBLE TIRE DISINTEGRATION/DIFFERENTIAL FAILURE COULD RESULT, CAUSING PERSONAL INJURY EXTENSIVE COMPONENT DAMAGE. USE AN OFF VEHICLE WHEEL AND TIRE BALANCER ONLY.

Most vibration in the rear end is caused by tires or driveline angle.

Vibration is a concern with modem, high-mileage tires if they are not "true" both radially and laterally. They are more susceptible to vibration around the limits of radial and lateral runout of the tire and wheel assembly. They also require more accurate balancing. Wheel and tire runout checks, truing and balancing are normally done before axle inspection.

DRIVELINE ANGLE





Driveline angularity is the angular relationship between the engine crankshaft, the driveshaft, and the rear axle pinion. Factors determining driveline angularity include ride height, rear spring, and engine mounts.

An incorrect driveline (pinion) angle can often be detected by the driving condition in which the vibration occurs.
- A vibration during coastdown from 72 to 56 km/h (45 to 35 mph) is often caused by an excessive U-joint angle at the axle (pinion nose downward).
- A vibration during acceleration, from 56 to 72 km/h (35 to 45 mph) may indicate an excessive U-joint angle at the axle (pinion nose upward).

When these conditions exist, check the driveline angles.

If the tires and driveline angle are not the cause, perform the NVH tests to determine whether the concern is caused by a condition in the axle.

UNIVERSAL JOINT (U-JOINT) WEAR
Place the vehicle on a frame hoist and rotate the driveshaft by hand. Check for rough operation or seized U-joints. Replace the U-joint if it shows signs of seizure, excessive wear, or improper seating.

AXLE FLANGE BOLT CIRCLE RUNOUT-SEMI-FLOATING AXLE

NOTE: The brake drums must be removed to perform all runout measurements.





1. Position the Dial Indicator with Bracketry perpendicular to the axle flange bolt, as close to the flange face as possible. Zero the indicator to allow the pointer to deflect either way.
2. Rotate the flange until the next bolt is contacted. Record the measurement and continue until each bolt is checked. The difference between the maximum and minimum contact readings will be the total axle flange bolt pattern runout. The runout must not exceed 0.39 mm (0.015 inch).

PILOT RUNOUT-SEMI-FLOATING AXLE





1. Position the Dial Indicator with Bracketry with the Clutch Housing Alignment Adapter to the pilot, as close to the axle flange face as possible. Zero the indicator to allow the pointer to deflect either way.
2. Rotate the flange one full turn and note the maximum and minimum readings. The difference between the maximum and minimum readings will be the total pilot runout. Pilot runout must not exceed 0.15 mm (0.006 inch).

AXLE FLANGE FACE RUNOUT-SEMI-FLOATING AXLE

NOTE: If the axle shaft assembly is removed, check runout of the shaft itself. The forged (unmachined) part of the shaft is allowed to have as much as 3.0 mm (0.120 inch) runout. This alone will not cause a vibration condition.





1. Position the Dial Indicator with Bracketry on the axle flange face, as close to the outer edge as possible. Zero the indicator to allow the pointer to deflect either way.
2. Rotate the flange one full turn and note the maximum and minimum readings. The difference between the maximum and minimum readings will be the total face runout. The runout must not exceed 0.127 mm (0.005 inch).

DRIVE PINION STEM AND COMPANION FLANGE
Check the companion flange runout when all other checks have failed to show the cause of vibration.

One cause of excessive companion flange runout is improper installation of the axle drive pinion seal.

Check to see if the spring on the seal lip has been dislodged before replacing the ring gear and pinion.

COUPLING SHAFT CENTER BEARING ALIGNMENT -158 AND 176 INCH WHEELBASE
Vehicle noise and vibration can be caused by a dislocated/failed driveshaft center bearing support rubber insulator, a contaminated driveshaft center bearing support or excessive compression of the rubber insulator.

BEARING SHIMMING
Drive-away shudder is the predominant symptom associated with driveline angles condition on vehicles with two-piece driveshafts. Drive-away shudder can usually be corrected by shimming down the driveshaft center bearing bracket.

If the drive-away shudder cannot be corrected by shimming down the driveshaft center bearing bracket, check the driveline angles.