Noise Conditions
Non-Axle NoiseThe five most common sources of non-axle noise are exhaust, tires, roof racks, trim mouldings and transmission.
Therefore, make sure that none of the following conditions are the cause of the noise before going with an axle teardown and diagnosis.
- In certain conditions, the pitch of the exhaust may sound very much like gear whine. At other times, it can be mistaken for a wheel bearing rumble.
- Tires, especially snow tires, can have a high-pitched tread whine or roar, similar to gear noise. Radial tires, to some degree, have this characteristic. Also, any non-standard tire with an unusual tread construction may emit a roar or whine-type noise.
- Trim and mouldings can also cause whistling or whining noise.
- Clunk may be a metallic noise heard when the automatic transmission is engaged in REVERSE or DRIVE, or it may occur when throttle is applied or released. It is caused by backlash somewhere in the driveline; it is felt or heard in the axle.
- Bearing whine is a high-pitched sound similar to a whistle. It is usually caused by malfunctioning pinion bearings, which are operating at driveshaft speed. Roller wheel bearings may whine the same way if they run completely dry. Bearing noise occurs at all driving speeds; this distinguishes it from gear whine, which usually comes and goes as speed changes.
- Bearing rumble sounds like marbles being tumbled. This condition is usually caused by a malfunctioning rear wheel bearing. The lower pitch is because the rear wheel bearing turns at about one-third of driveshaft speed.
- Rear wheel bearing noise might be mistaken for pinion bearing noise, so always look at the rear wheel bearings carefully before tearing down the axle. Pinion bearings make a high-pitched, whistling noise, usually at all speeds. However, if only one differential pinion bearing is malfunctioning, the noise may vary in different driving phases. Bearings should not be replaced unless they are actually scored or damaged.
Rear wheel bearings are pressed into the rear axle housing, making them more difficult to check. However, the axle shaft is the inner race for the bearing. So if the rear wheel bearings are damaged, the roller surface on the axle shaft will be damaged as well. The rollers run on the center of the polished surface.
Noise Conditions
The noises described as follows usually have specific causes that can be diagnosed by observation as the unit is disassembled. The initial clues are the type of noise heard during the road test.
- Gear noise is typically a howling or whining of the differential ring gear and pinion 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.
- 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 vehicle speed.
- Knock is very similar to chuckle, though it may be louder and occurs on acceleration or deceleration. The teardown will disclose what service is required.
- Chatter noise on Traction-Lok� axles can usually be traced to erratic movement between adjacent clutch components and can sometimes be corrected with a lubricant change and the addition of Additive Friction Modifier C8AZ-19B546-A or equivalent meeting Ford specification EST-M2C118-A.
- Click at engagement is a slight noise, distinct from a clunk, that happens in REVERSE or DRIVE engagement. Check for the presence of a pinion oil slinger.
- Axle shaft noise is similar to gear noise and pinion bearing whine. However, rear wheel 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 a certain speed. If vehicle displays above noise condition upon ride evaluation, remove suspect axle shafts, replace inner wheel bearing oil seals and install a new set of axle shafts. Re-evaluate vehicle for noise before removing any internal rear axle components.
- Boom occurs when ring gear teeth have a runout of more than 0.10 mm (0.004 inch).
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.
This condition can be corrected and the noise eliminated 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), replace the gearset.
If either gear is scored or badly damaged, the differential ring gear and pinion must be replaced. Also, if metal has broken loose, the rear axle housing must be cleaned to remove particles that could cause damage later. Any other damaged parts in the axle must be replaced.
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.
Check and rule out tires, exhaust and trim items before disassembling the axle to diagnose and correct gear noise.
Knock, which can occur on all driving phases, has several causes. In most cases, one of the following conditions has occurred:
- 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.
- Knock is also characteristic of excessive end play in the axle shaft. The frequency of knock will be less because the axle shaft speed is slower than the driveshaft.
NOTE: Be sure to measure axle shaft end play with a dial indicator, not by feel.
On the integral axle, end play is allowable up to 0.762 mm (0.030 inch). It is controlled by the u-washer that holds the axle shaft in the pocket of the differential side gear.