Front Steering Knuckle: Testing and Inspection
Analysis of VibrationWARNING: A vehicle equipped with a (Traction-Lok) differential will always have both wheels driving. If only one wheel is raised of the floor and the rear axle is driven by the engine, the wheel on the floor could drive the vehicle of 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 in Vehicle/Testing and Inspection 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 crankshaft, the driveshaft and the rear axle pinion. Factors determining driveline angularity include ride height and engine mounts.
Driveline Angle:
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, carry out the NVH tests to determine whether the concern is caused by a condition in the axle.
Universal Joint (U-Joint) Wear
WARNING: The electrical power to the air suspension system must be shut off prior to hoisting, jacking or towing an air suspension vehicle. This can be accomplished by turning off the air suspension switch. Failure to do so can result in unexpected inflation or deflation of the air springs, which can result in shifting of the vehicle during these operations.
Place the vehicle on a frame hoist and rotate the driveshaft by hand. Check for rough operation or seized U-Joints. Install a new U-Joint if it shows signs of seizure, excessive wear or incorrect seating.
Wheel Hub or Axle Flange Bolt Circle Runout
NOTE: The brake discs must be removed to carry out all runout measurements.
1. Position the Dial Indicator Gauge with Holding Fixture perpendicular to the wheel hub or axle flange bolt, as close to the hub or flange face as possible. Zero the indicator to allow the pointer to deflect either way.
2. Rotate the hub or 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 wheel hub or axle flange bolt pattern runout. The runout must not exceed 0.38 mm (0.015 inch).
Pilot Runout
1. Position the Dial Indicator Gauge with Holding Fixture with the Clutch Housing Gauge to the pilot, as close to the hub or axle flange face as possible. Zero the indicator to allow the pointer to deflect either way.
2. Rotate the hub or 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).
Wheel Hub or Axle Flange Face Runout
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 Gauge with Holding Fixture on the wheel hub or 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 hub or 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 Pinion Flange
Check the pinion flange runout when all other checks have failed to show the cause of vibration.
One cause of excessive pinion flange runout is incorrect installation of the axle drive pinion seal. Check to see if the spring on the seal lip has been dislodged before installing a new ring gear and pinion.