Gear Noise

Gear Howl and Whine

Before disassembling the axle to diagnose and correct gear noise, it is important that the tires, exhaust, trim items, roof racks and axle shafts/wheel bearings be checked as possible causes.

The noises described under Road Test usually have specific causes that can be diagnosed by observation as the unit is disassembled. The initial clues are, of course, the type of noise heard on the road test and the driving conditions.

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, or by a damaged tooth on the coast side of the pinion or ring gear.

Any damage to a gear tooth on the coast side can cause a noise identical to chuckle. Even a very small tooth nick or ridge on the edge of a tooth is enough to cause the noise.

You can often correct this condition and eliminate the noise simply by cleaning up the gear tooth nick or ridge with a small grinding wheel. If the cleaned up or damaged area is larger than 3.2mm (1/8 inch), it is advisable to replace the gearset.

To check the gearset, 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, the gearset must be replaced. Also, if there is metal broken loose, the carrier and housing must be cleaned to remove particles that could cause damage later. Any other damaged parts in the axle must be replaced.

Damaged Gear Teeth






Scored Gear Teeth

Knock

Knock, which can occur on all driving phases, has several causes. In most cases, you will discover one of the following conditions:

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. Occasionally, the ring gear bolts will knock against the inside of the carrier casting. The cause may be too little clearance due to casting flash or bumps. In this case, the differential case can be removed and the interference points ground out.

   Another possibility is simply that one or more bolts are slightly backed-out. Remove, replace and properly tighten the bolts using Stud and Bearing Mount E0AZ-19554-BA (WSK-M2G349-A1) or equivalent, on the threads.

3. Knock is also characteristic of excessive end play in the axle shafts. Up to 0.762mm (0.030 inch) is allowed in most axles. The frequency of knock will be less because the axle shaft speed is slower than the driveshaft.

   NOTE: Be sure to measure the end play with a dial indicator, not by feel. A guess usually feels like far more end play than there actually is.

Clunk

Clunk is due to backlash in the driveline or loose rear suspension components. To determine whether driveline clunk is caused by the axle, make a check of the total axle backlash as follows.

1. Raise the vehicle on a frame or twin post hoist so that the rear wheels are free. Refer to Section 00-02.

2. To maintain driveline balance, mark the rear driveshaft yoke and axle companion flange so they may be installed in their original positions

3. Remove the flange bolts and disconnect the driveshaft from the axle companion flange. Support the driveshaft.

4. Install Companion Flange Holding Tool T78P-4851-A between the circular companion flange and a part of the frame or body so that the flange cannot move.

5. Lock the LH rear wheel to keep it from turning.

6. Using a torque wrench, and locating on one of the wheel nuts, rotate RH wheel slowly until a torque of 6.8-8.1 Nm (5-6 lb-ft) is obtained. Hold a chalk marker on side of tire 304.8mm (12 inch) from center of wheel.
   
   
   
   

7. Rotate wheel slowly in opposite direction until a torque of 6.8-8.1 Nm (5-6 lb-ft) is obtained.

8. Measure the length of the chalk mark; which is the total axle backlash. Total axle backlash should be 25.4mm (1 inch) or less.

   If the backlash is within this limit, the clunk will not be eliminated by going into the axle.

   Check for these conditions if the backlash is excessive.

   • Elongation of the differential pinion shaft holes in the differential case.
   • Missing differential or side gear washer.
   • Galling of the differential pinion shaft and bore.

   If none of the above conditions show up, there may be a loose fit of the axle shafts to the side gear splines. You should continue as follows until the correction is made.

9. Install new side gears and check the backlash.

10. Install two new axle shafts.

11. Replace the differential case.

12. Install the driveshaft so the index mark on the rear yoke is in-line with the index mark on the axle companion flange. This ensures original driveline balance. If vibration exists after installation, refer to Section 00-04.

13. Tighten all flange bolts to 95-130 Nm (70-95 lb-ft).

Bearing Noise

Bearing malfunctions will normally be obvious at disassembly. As noted earlier, pinion bearings make a high-pitched, whistling noise, usually at all speeds. However, if there is only one pinion bearing that is malfunctioning, the noise may vary in different driving phases.

Pinion bearings are frequently replaced on axles with low mileage under 24,139 km (15,000 miles), unnecessarily when correcting gear noise. They should not be replaced unless they are actually scored or damaged, or there is a specific pinion bearing noise. Examine the large end of the rollers for wear. If the bearings original blend radius has worn to a sharp edge, the bearing should be replaced.

Remember that the low-pitched rumble of a malfunctioning wheel bearing can be duplicated by an exterior luggage rack or by tires.

Wheel bearing noise might be mistaken for pinion bearing noise, so be sure to look at the wheel bearings carefully before tearing down the axle.

Wheel bearings are pressed into the axle housing tubes, making them more difficult to check. However, the axle shaft is the inner race for the bearing. If the bearing is damaged, the roller surface on the axle shaft may be damaged as well. The rollers run on approximately the center of the polished surface.

Bearing Preload Check

The absence of differential bearing preload causes noise as driving loads tend to move the gear pattern out of position.

Both the pinion bearing and differential bearing preload must be checked to ensure that the pattern will stay in place under load.

Check the pinion bearing preload by removing wheels and brake drums and putting a Nm (lb-in) torque wrench on the pinion nut and measuring the torque effort it takes to turn the pinion. Compare the reading with the preload specification for used bearings. Refer to Section 05-02A or Section 05-02B for specifications.

NOTE: These preload readings are to be made when the axle assembly is at room temperature or above. Cold lube will give a false reading.

If any end play or radial play can be detected when applying a force by hand, the pinion bearings are not preloaded.

NOTE: The absence of preload here may indicate that one or more of the components (i.e., bearings, slinger spacer or flange) is worn or damaged.

Bent Axle Housing—Analysis

It is important to check for a bent axle housing anytime a vehicle has sustained structural damage or unusual tire wear is noted. A quick check can be performed any time damage to the rear axle housing is suspected.

Axle Alignment Inspection, Rear

1. Raise the vehicle on a hoist to allow the axle to be freely suspended. Refer to Section 00-02.

2. Using white chalk or paint, mark a small area at the center of each rear tire and scribe a vertical line on it.
   
   
   
   

3. Adjust both wheels so that the markings face the front of the vehicle. Using a tape measure, measure the distance between scribe marks and record this reading (front reading).
   
   
   
   

4. Rotate the rear wheels so that the markings are directly underneath the vehicle. Measure the distance between the scribe marks and record this reading (bottom reading).
   
   
   
   

5. Rotate the rear wheels so the markings face the rear of the vehicle. Again, measure and record the distance between scribe marks (rear reading).
   
   
   
   

6. The difference between the front and rear readings is the toe out or toe in condition of the housing (Steps 3 and 5).

   Example:

   1. Front Reading: 157.9cm (62-3/16 inch)
   2. Rear Reading: 157.6cm (62-1/16 inch)
   3. Toe Out: 3.1mm (1/8 inch)

      Toe in occurs when the front reading is less than the rear reading.

7. To determine camber, find the average of the front and rear readings (obtained in Steps 3 and 5). Then, subtract the bottom reading from this (obtained in Step 4).

   Example:

   1. Average of Front and Rear Readings: 158.1cm (62-1/8 inch)
   2. Bottom Reading: 158.1cm (62-1/8 inch)
   3. Difference or Camber: 0mm (0 inch)

      Positive (+) camber is when the bottom reading is less than the average of the front and rear readings. Negative (-) camber is when the bottom reading is greater than the average of the front and rear readings.

8. Results of the measurements taken must conform to the following specifications:
   1. Camber 0 ± 3.9mm (0 ±5/32 inch)
   2. Toe In 0 - 1.58mm (0-1/16 inch)
   3. Toe Out 0 - 4.7mm (0-3/16 inch)

      If the rear axle assembly does not meet this specification, it must be replaced.

9. If rear axle is replaced, repeat Steps 2 through 7.