Noise
GEAR HOWL AND WHINEHowling or whining of the ring gear and pinion is due to an improper gear pattern, gear damage or improper bearing preload. It can occur at various speeds and driving conditions or it can be continuous.
Before disassembling the axle to diagnose and correct gear noise, eliminate the tires, exhaust, trim items, roof racks and axle shafts and rear wheel bearings as possible causes.
The noises identified during a 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 is a particular rattling noise that sounds like a stick against the spokes of a spinning bicycle wheel. It occurs while decelerating from 64 km/h (40 mph) and can usually be heard all the way to a stop. The frequency varies with the speed of the vehicle.
Chuckle that occurs on the coast driving phase is usually caused by excessive clearance between the differential gear hub and the differential case bore. It can also be caused 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.
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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 3.2 mm (1/8 inch), it is advisable to replace the gear set.
To check the differential 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, the differential ring gear and pinion must be replaced. If there is metal broken loose, the rear axle housing must also be cleaned to remove particles that could cause damage later. Any other damaged parts in the rear axle housing must be replaced.
KNOCK
Knock, which can occur on all driving phases, has several causes. In most cases, the technician 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. Knock is also characteristic of excessive end play in the axle shafts. Up to 0.762 mm (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 and not by feel.
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 the wheels are free.
2. To maintain driveline balance, mark rear driveshaft centering socket yoke and rear axle universal joint flange so they may be installed in their original positions.
3. Remove bolts and disconnect driveshaft from the rear axle universal joint flange. Support driveshaft.
4. Install Companion Flange Holding Tool 205-126 (T78P-4851-A) between the rear axle universal joint flange and a part of the frame or body so that the rear axle universal joint flange cannot move.
5. Lock the LH rear wheel to keep it from turning.
6. Hold a chalk marker on side of tire 304.8 mm (12 inches) from center of wheel. With a torque wrench placed on one of the lug nuts, rotate RH wheel slowly to a torque of 7 - 8 Nm (62 - 70 inch lbs.).
7. Rotate wheel slowly in opposite direction to a torque of 7 - 8 Nm (62 - 70 inch lbs.).
8. Measure the length of the chalk mark which is the total axle backlash. Total axle backlash should be 25.4 mm (1 inch) or less. If the backlash is within this limit, the clunk will not be eliminated by disassembling the axle.
Check for these conditions if the backlash is excessive:
a. elongation of the differential pinion shaft holes in the differential case
b. missing differential pinion thrust washer or differential side gear thrust washer
c. galling of the differential pinion shaft and bore
If none of these conditions is present, there may be a loose fit of the axle shafts to the side gear splines. Continue as follows until the correction is made.
9. Install new differential 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 driveshaft slip yoke is in-line with the index mark on the driveshaft centering socket yoke. This maintains original driveline balance.
13. Tighten rear axle universal joint flange bolts to 95 - 130 Nm (70 - 95 ft. lbs.).
BEARING WHINE
Bearing whine is a high-pitched sound similar to a whistle. It is usually caused by 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. However, if there is only one differential pinion bearing (462 1), malfunctioning, the noise may vary in different driving phases.
Bearing damage will normally be obvious at disassembly. As noted earlier, differential pinion bearings make a high-pitched whistling noise, usually at all speeds. However, if there is only one damaged differential pinion bearing, the noise may vary in different driving phases.
Differential pinion bearings are frequently replaced unnecessarily on axles with mileage under 24,139 km (115,000 miles) when correcting gear noise. They should not be replaced unless they are actually scored or damaged, or there is a specific differential pinion bearing noise. Examine the large end of the rollers for wear. If the differential pinion bearing original blend radius has worn to a sharp edge, the differential pinion bearing should be replaced.
Remember that the low-pitched rumble of a damaged wheel bearing can also be caused by the exterior luggage rack or tires.
Rear wheel bearing noise might be mistaken for pinion bearing noise. Look at the rear wheel bearing carefully before tearing down the axle.
Rear 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 also be damaged. The rollers run approximately on the center of the polished surface.
CHATTER ON CORNERS
Chatter noise on Traction-Lok axles can usually be traced to erratic movement between adjacent clutch plates and can be corrected with a lubricant change that includes Additive Friction Modifier C8AZ-191B546-A or equivalent meeting Ford specification EST-M2C118-A.
CLICK AT ENGAGEMENT
Click at engagement is a condition on axles of a slight noise, distinct from a clunk, that happens in REVERSE or DRIVE engagement. Correct this condition by installing a rear axle drive pinion shaft oil slinger between the rear axle universal joint flange and differential pinion bearing.
AXLE SHAFT NOISE
Axle shaft noise is similar to gear noise and differential pinion bearing whine. However, axle shaft bearing noise will normally distinguish itself from gear noise by occurring in all driving modes (drive, coast and float) and will persist with transmission in NEUTRAL while vehicle is moving at problem speed. If the vehicle makes this noise, remove suspect axle shafts, replace rear wheel bearings and install a new set of axle shafts. Re-evaluate vehicle for noise before removing any internal components.
BEARING RUMBLE
Bearing rumble sounds like marbles being tumbled. This condition is usually caused by a malfunctioning pilot bearing. The lower pitch is because the pilot bearing turns at only about one-third of driveshaft speed.
Bearing malfunctions will normally be obvious at disassembly. As noted earlier, damaged 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 unnecessarily on axles with mileage under 24,139 km (15,000 miles) 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 bearing's original blend radius has worn to a sharp edge, the bearing roller and cup should be replaced.