Noises
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, it is important that the tires, exhaust, trim items and axle shaft/rear wheel bearings be eliminated 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 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 may 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.
WARNING: ALWAYS WEAR SAFETY GOGGLES. IF SOLVENT OR COMPRESSED AIR GETS IN YOUR EYES, SEVERE IRRITATION OR PERMANENT INJURY SUCH AS BLINDNESS COULD RESULT. SEEK MEDICAL ATTENTION IMMEDIATELY.
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 (1.25 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. Also, 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 axle 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. NOTE: Measure the end play with a dial indicator and not by feel. Guessing is inaccurate.
Knock is also characteristic of excessive end play in the axle shaft. 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.
CLUNK
Special Tool:
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 rear wheels are free.
2. To maintain driveline balance, mark the driveshaft centering socket yoke and rear axle universal joint flange so they may be installed in their original positions.
3. Remove the flange bolts and disconnect the driveshaft from the rear axle universal joint flange. Support the 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. Using a torque wrench, and locating on one of the lug nuts, rotate RH wheel slowly until a torque of 6-8 Nm (54-70 inch lbs.) is obtained. Hold a chalk marker on side of tire 304.8 mm (12 inch) from center of wheel.
7. Rotate wheel slowly in opposite direction until a torque of 6-8 Nm (54-70 inch lbs.) is obtained.
8. Measure the length of the chalk mark to obtain 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 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 pinion thrust washer or differential side gear thrust 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 shaft to the differential side gear splines. You should 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 u-washer.
12. Install the driveshaft so the index mark on the rear yoke is in-line with the index mark on the rear axle universal joint flange. This restores original driveline balance. If vibration exists after installation.
13. Tighten all flange bolts to 93-130 Nm (69-95 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 that is damaged, 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 (15,000 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 be duplicated by an exterior luggage rack or tires.
Rear wheel bearing noise might be mistaken for pinion bearing noise so 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 as well. The rollers run on approximately the center of the polished surface.
CHATTER ON CORNERS
Chatter on corners is a condition where the whole rear end vibrates when the vehicle is turning. The vibration is plainly felt and heard. In conventional axles, extra differential thrust washers cause a partial lockup that creates this chatter. Chatter noise on Traction-Lok axles can usually be traced to erratic movement between the adjacent clutch plates and can be corrected with a lubricant change that includes the addition of Additive Friction Modifier C8AZ-1913546-A or equivalent meeting Ford specification EST-M2C 1 18-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.