By all means, You already know i'm not an expert on this, but here's some Diagnostic Chart if it helps.
DIAGNOSIS AND TESTING
GEAR NOISE
Axle gear noise can be caused by insufficient lubricant, incorrect backlash, incorrect pinion depth, tooth contact, worn/damaged gears, or the carrier housing not having the proper offset and squareness.
Gear noise usually happens at a specific speed range. The noise can also occur during a specific type of driving condition. These conditions are acceleration, deceleration, coast, or constant load.
When road testing, first warm-up the axle fluid by driving the vehicle at least 5 miles and then accelerate the vehicle to the speed range where the noise is the greatest. Shift out-of-gear and coast through the peak-noise range. If the noise stops or changes greatly:
- Check for insufficient lubricant.
- Incorrect ring gear backlash.
- Gear damage.
Differential side gears and pinions can be checked by turning the vehicle. They usually do not cause noise during straight-ahead driving when the gears are unloaded. The side gears are loaded during vehicle turns. A worn pinion shaft can also cause a snapping or a knocking noise.
BEARING NOISE
The axle shaft, differential and pinion bearings can all produce noise when worn or damaged. Bearing noise can be either a whining, or a growling sound.
Pinion bearings have a constant-pitch noise. This noise changes only with vehicle speed. Pinion bearing noise will be higher pitched because it rotates at a faster rate. Drive the vehicle and load the differential. If bearing noise occurs, the rear pinion bearing is the source of the noise. If the bearing noise is heard during a coast, the front pinion bearing is the source.
Worn or damaged differential bearings usually produce a low pitch noise. Differential bearing noise is similar to pinion bearing noise. The pitch of differential bearing noise is also constant and varies only with vehicle speed.
Axle shaft bearings produce noise and vibration when worn or damaged. The noise generally changes when the bearings are loaded. Road test the vehicle. Turn the vehicle sharply to the left and to the right. This will load the bearings and change the noise level. Where axle bearing damage is slight, the noise is usually not noticeable at speeds above 30 mph.
LOW SPEED KNOCK
Low speed knock is generally caused by a worn U-joint or by worn side–gear thrust washers. A worn pinion shaft bore will also cause low speed knock.
VIBRATION
Vibration at the rear of the vehicle is usually caused by a:
- Damaged drive shaft.
- Missing drive shaft balance weight(s).
- Worn or out-of-balance wheels.
- Loose wheel lug nuts.
- Worn U-joint(s).
- Loose/broken springs.
- Damaged axle shaft bearing(s).
- Loose pinion gear nut.
- Excessive pinion yoke run out.
- Bent axle shaft(s).
Check for loose or damaged front-end components or engine/transmission mounts. These components can contribute to what appears to be a rearend vibration. Do not overlook engine accessories, brackets and drive belts.
NOTE: All driveline components should be examined before starting any repair.
DRIVELINE SNAP
A snap or clunk noise when the vehicle is shifted into gear (or the clutch engaged), can be caused by:
- High engine idle speed.
- Transmission shift operation.
- Loose engine/transmission/transfer case mounts.
- Worn U-joints.
- Loose spring mounts.
- Loose pinion gear nut and yoke.
- Excessive ring gear backlash.
- Excessive side gear to case clearance.
The source of a snap or a clunk noise can be determined with the assistance of a helper. Raise the vehicle on a hoist with the wheels free to rotate. Instruct the helper to shift the transmission into gear. Listen for the noise, a mechanics stethoscope is helpful in isolating the source of a noise.
DIAGNOSTIC CHART
Condition Possible Causes Correction Wheel Noise 1. Wheel loose. 1. Tighten loose nuts. 2. Faulty, brinelled wheel bearing. 2. Replace bearing. Axle Shaft Noise 1. Misaligned axle tube. 1. Inspect axle tube alignment. Correct as necessary. 2. Bent or sprung axle shaft. 2. Inspect and correct as necessary. Axle Shaft Broke 1. Misaligned axle tube. 1. Replace the broken shaft after correcting tube mis-alignment. 2 Vehicle overloaded. 2. Replace broken shaft and avoid excessive weight on vehicle. 3. Erratic clutch operation. 3. Replace broken shaft and avoid or correct erratic clutch operation. 4. Grabbing clutch. 4. Replace broken shaft and inspect and repair clutch as necessary. Differential Cracked 1. Improper adjustment of the differential bearings. 1. Replace case and inspect gears and bearings for further damage. Set differential bearing pre-load properly. 2. Excessive ring gear backlash. 2. Replace case and inspect gears and bearings for further damage. Set ring gear backlash properly. 3. Vehicle overloaded. 3. Replace case and inspect gears and bearings for further damage. Avoid excessive vehicle weight. 4. Erratic clutch operation. 4. Replace case and inspect gears and bearings for further damage. Avoid erratic use of clutch. Differential Gears Scored 1. Insufficient lubrication. 1. Replace scored gears. Fill differential with the correct fluid type and quantity. 2. Improper grade of lubricant. 2. Replace scored gears. Fill differential with the correct fluid type and quantity. 3. Excessive spinning of one wheel/tire. 3. Replace scored gears. Inspect all gears, pinion bores, and shaft for damage. Service as necessary. Loss Of Lubricant 1. Lubricant level too high. 1. Drain lubricant to the correct level. 2. Worn axle shaft seals. 2. Replace seals. 3. Cracked differential housing. 3. Repair as necessary. 4. Worn pinion seal. 4. Replace seal. 5. Worn/scored yoke. 5. Replace yoke and seal. 6. Axle cover not properly sealed. 6. Remove, clean, and re-seal cover. Axle Overheating 1. Lubricant level low. 1. Fill differential to correct level. 2. Improper grade of lubricant. 2. Fill differential with the correct fluid type and quantity. 3. Bearing pre-loads too high. 3. Re-adjust bearing pre-loads. 4. Insufficient ring gear backlash. 4. Re-adjust ring gear backlash. Gear Teeth Broke 1. Overloading. 1. Replace gears. Examine other gears and bearings for possible damage. 2. Erratic clutch operation. 2. Replace gears and examine the remaining parts for damage. Avoid erratic clutch operation. 3. Ice-spotted pavement. 3. Replace gears and examine remaining parts for damage. 4. Improper adjustments. 4. Replace gears and examine remaining parts for damage. Ensure ring gear backlash is correct. Axle Noise 1. Insufficient lubricant. 1. Fill differential with the correct fluid type and quantity. 2. Improper ring gear and pinion adjustment. 2. Check ring gear and pinion contact pattern. Adjust backlash or pinion depth. 3. Unmatched ring gear and pinion. 3. Replace gears with a matched ring gear and pinion. 4. Worn teeth on ring gear and/or pinion. 4. Replace ring gear and pinion. 5. Loose pinion bearings. 5. Adjust pinion bearing pre-load. 6. Loose differential bearings. 6. Adjust differential bearing pre-load. 7. Mis-aligned or sprung ring gear. 7. Measure ring gear run-out. Replace components as necessary. 8. Loose differential bearing cap bolts. 8. Inspect differential components and replace as necessary. Ensure that the bearing caps are torqued tot he proper specification. 9. Housing not machined properly. 9. Replace housing.
