Wheel Hub: Testing and Inspection
Inspection and VerificationCertain axle noise or vibration symptoms are also common to the engine, transmission, wheel bearings, tires and other parts of the vehicle. For this reason, be sure that the cause of the concern is in the axle before disassembling, adjusting or repairing the axle. Refer to Vehicle/Testing and Inspection.
Certain driveshaft vibration symptoms are common to the front engine accessory drive (FEAD), the engine, transmission or tires. Be sure the cause of the concern is the driveshaft before repairing or installing a new driveshaft.
Noise Acceptability
NOTE: A gear-driven unit will produce a certain amount of noise. Some noise is acceptable and audible at certain speeds or under various driving conditions such as a newly paved blacktop road. Slight noise is not detrimental to the operation of the axle and is considered normal.
With a limited slip differential axle, slight chatter or groaning noise on slow turns after extended highway driving is considered acceptable and has no detrimental effect on the locking axle function.
Universal Joint (U-Joint) Inspection
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.
Analysis of Leakage
Clean up the leaking area enough to identify the exact source. An axle leak can be caused by:
^ Axle lubricant level is too high
^ Worn or damaged axle shaft hub seals or differential seals
^ Differential housing or cover is cracked
^ Pinion seal is worn or damaged
^ Pinion flange is scored or damaged
^ Axle cover is not sealed
^ Vent is plugged, loose or missing
Repair the axle as necessary. Make sure the axle lubricant is at the correct level.
Axle Vent
NOTE: If a plugged vent cannot be cleared, install a new one.
A plugged vent will cause excessive seal lip wear due to internal pressure buildup. If a leak occurs, check the vent. Make sure the vent hose is not kinked. Remove the hose from the vent nipple and clear the hose of any foreign material.
While the hose is removed, pass a length of mechanic's wire or a small-diameter Allen wrench in and out of the vent to clean it. Connect the hose when done.
Pinion Flange Seal
Leaks at the axle drive pinion seal originate for these reasons:
^ Contamination
^ Seal was not correctly installed
^ Poor quality axle surface(s)
Any damage to the seal bore (dings, dents, gouges or other imperfections) will distort the seal casing and allow leakage past the outer edge of the axle drive pinion seal.
The axle drive pinion seal can be torn, cut or gouged if it is not installed carefully. The spring that holds the axle drive pinion seal against the pinion flange may be knocked out and allow leakage past the lip.
The rubber lips can occasionally become hard (like plastic) with cracks at the oil lip contact point. The contact point on the pinion flange may blacken, indicating excessive heat. Marks, nicks, gouges or rough surface texture on the seal journal of the pinion flange will also cause leaks.
Install a new pinion flange if any of these conditions exist.
Metal chips or sand trapped at the sealing lip can also cause oil leaks. This can cause a wear groove on the pinion flange and heavy pinion seal wear.
When a seal leak occurs, install a new seal and check the vent and the vent hose to make sure they are clean and free of foreign material.
Axle Shaft Seals
Axle shaft oil seals are susceptible to the same kinds of damage as axle drive pinion seals if incorrectly installed. The seal bore must be clean and the lip handled carefully to avoid cutting or tearing it. The axle shaft journal surface must be free of nicks, gouges and rough surface texture.
Analysis of Vibration
WARNING: A vehicle equipped with a limited slip 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 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 can 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 or imbalance.
Vibration is a concern with modern, 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. On a vibration concern, follow the diagnostic procedure in Vehicle/Testing and Inspection. They also require more accurate balancing. Wheel and tire runout checks, truing and balancing are normally done before axle inspection.
Driveline Angle
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, carry out the NVH tests to determine whether the concern is caused by a condition in the axle. Refer to Vehicle/Testing and Inspection.
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. Install a new U-joint if it shows signs of seizure, excessive wear or incorrect seating.
Axle Flange Bolt Circle Runout - Semi-Floating Axle
NOTE: The brake discs or drums must be removed to carry out all runout measurements.
1. Position the Dial Indicator Gauge with Holding Fixture 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 0.13 mm (0.005 inch.)
Pilot Runout - Semi-Floating Axle
1. Position the Dial Indicator Gauge with Holding Fixture with the Clutch Housing Gauge 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 0.076 mm (0.003 inch).
Axle Flange Face Runout - Semi-Floating Axle
1. Position the Dial Indicator Gauge with Holding Fixture 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 0.13 mm (0.005 inch).
3. Full float axles in E-350 and E-450 models have hubs, which have the same 0.13 mm (0.005 inch) limit on the flange lateral runout.
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 determine if the spring on the seal lip has been dislodged before installing a new 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 angle conditions on vehicles with 2-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.
Axle Noise
NOTE: Before disassembling the axle to diagnose and correct gear noise, eliminate the tires, exhaust, trim items, roof racks, axle shafts and wheel bearings as possible causes. Follow the diagnostic procedures in Vehicle/Testing and Inspection.
The noises described as follows usually have specific causes that can be diagnosed by observation as the unit is disassembled. The initial clue is the type of noise heard during the road test.
Gear Howl and Whine
Howling or whining of the ring gear and pinion is due to an incorrect gear pattern, gear damage or incorrect bearing preload.
Bearing Whine
Bearing whine is a high-pitched sound similar to a whistle. It is usually caused by worn/damaged pinion bearings, which are operating at driveshaft speed. Bearing noise occurs at all driving speeds. This distinguishes it from gear whine, which usually comes and goes as speed changes.
As noted, pinion bearings make a high-pitched, whistling noise, usually at all speeds. If, however, there is only one pinion bearing that is worn/damaged, the noise may vary in different driving phases. New pinion bearings must not be installed unless they are scored or damaged or there is a specific pinion bearing noise. A worn/damaged bearing will normally be obvious at disassembly.
Examine the large end of the rollers for wear. If the pinion bearing's original blend radius has worn to a sharp edge, the pinion bearing must be installed new.
NOTE: A low-pitched rumble normally associated with a worn/damaged wheel bearing can be caused by the exterior luggage rack or tires.
Wheel bearing noise, though usually lower pitched, can be mistaken for a pinion bearing noise. Check the wheel bearing for a spalled cup and spalled/damaged rollers. Install a new wheel bearing if any of these concerns are detected.
If the wheel bearing is damaged, the roller surface on the axle shaft may also be damaged. Install a new axle shaft if any damage is detected.
Bearing Rumble
Bearing rumble sounds like marbles being tumbled. This condition is usually caused by a worn/damaged wheel bearing. The lower pitch is because the wheel bearing turns at only about 1/3 of the driveshaft speed. Wheel bearing noise also may be high-pitched, similar to gear noise, but will be evident in all 4 driving modes.
Axle Shaft Bearing Noise
Axle shaft bearing noise is similar to gear noise and differential pinion bearing whine. Axle shaft bearing noise will usually distinguish itself from gear noise by occurring in all driving modes (drive, coast and float), and will persist with the transmission in NEUTRAL while the vehicle is moving at the speed in which the concern is occurring.
If the vehicle makes this noise, remove the suspect axle shaft, install a new bearing and a new axle seal. Re-evaluate the vehicle for noise before removing any internal components.
Chuckle
Chuckle that occurs on the coast driving phase is usually caused by excessive clearance between the differential gear hub and the differential case bore.
Damage to a gear tooth on the coast side can cause a noise identical to a chuckle. A very small tooth nick or ridge on the edge of a tooth can cause the noise.
Clean the gear tooth nick or ridge with a small grinding wheel. If the damaged area is larger than 3.2 mm (1/8 inch), install a new gearset.
To check the ring gear and pinion, remove as much lubricant as possible from the gears with clean solvent. Wipe the gears dry or blow them dry with compressed air. Look for scored or damaged teeth. Also look for cracks or other damage.
If either gear is scored or damaged badly, install a new ring gear and pinion.
If metal has broken loose, the axle housing must be cleaned to remove particles that will cause damage. At this time, any other damaged parts in the axle housing must also be installed new.
Knock
Knock, which can occur during all driving phases, has several causes, including damaged teeth or gearset.
In most cases, one of these conditions will occur:
1. A gear tooth damaged on the drive side is a common cause of the knock. This can usually be corrected by grinding the damaged area.
2. NOTE: Measure the end play with a Dial Indicator Gauge with Holding Fixture and not by feel.
Knock is also caused by excessive in-out end play in the axle shafts. Up to 0.76 mm (0.030 inch) is allowed in semi-float axles. The frequency of the knock will be less because the axle shaft speed is slower than the driveshaft.
Clunk
Clunk is a metallic noise heard when the automatic transmission is engaged in REVERSE or DRIVE. The noise can also occur when throttle is applied or released. It is caused by backlash somewhere in the driveline or loose suspension components; it is felt or heard in the axle.
Additionally, clunk may be heard upon initial drive-away. This occurs as engine torque shifts vehicle weight, forcing changes in driveline angles, preventing the driveshaft slip-yoke from sliding on the output shaft. To correct for this condition, lubricate the slip-yoke splines.