Noise is usually the first sign of trouble in the drive axles or differential. The kind of noise you hear can help you determine what is the exact cause of the trouble. But we should how to determine the same. The noise can be a humming noise, a growl or a knocking noise. Also we have to make sure that which activity causes the noise. i.e. The noise is produced when the vehicle runs straight , or noise is produced when the vehicle is taking a turn. You have to note whether the noise is louder when the engine is driving the vehicle or when the vehicle is coasting. Ring and pinion gear noise changes with vehicle speed and is usually unaffected by loads and turns. It is difficult to diagnose the drive axle and the differential noise by running the vehicle in the shop with the wheels raised, road testing is the best method to diagnose such noise in the vehicle, sometimes the noise can be heard while running the vehicle on a chassis dynamometer.
The major troubles found in Rear Axles can be classified as under:-
1. Humming Noise:
A humming noise is often caused by an incorrectly installed ring and gear pinion, which needs to be adjusted, the incorrect installation of ring and pinion gear prevents proper tooth contact and can cause rapid tooth wear and can cause gear failure. This humming noise converts into growling noise when the wear increases. Humming noise can also be caused due to worn out bearings, which needs to be replaced.
The adjustment procedure of the ring and pinion gear is as under:
Before removing the differential, measure the pinion bearing preload and ring gear backlash. Also check the ring gear tooth contact pattern. To study this pattern wipe off the lubricant from the differential carrier and clean each tooth on the ring gear. Dip a small brush in a gear marking compound preferably, Prussian blue. Make a coating of this on the drive and the coast sides of the ring gear teeth. Slightly load the ring and pinion gears, and rotate the ring gear one complete revolution in each direction. This leaves a distinct contact pattern on both sides of ring gear teeth.
2. Noise on acceleration :
Noise that is louder during vehicle acceleration probably means there is heavy contact on the outer ends of the ring gear teeth. Noise that is louder when the vehicle is casting probably means there is heavy tooth contact. A loud clunk during acceleration or deacceleration may be caused by excess clearance between an axle shaft and a differential side gear. The noise may be caused by excessive clearance between the pinion gears and side gears in the differential.
3. Knocking Noise:
The knocking or clicking sound may be due to the worn out splines of the axle shafts in which case the defective shaft has to be replaced. Another reason for this may be chipped teeth of some gears in the rear axle, which has to be replaced.
4. Noise on curves:
The noise which is heard when the vehicle is taking a turn, is due to the trouble in the axle shaft or is due to a problem in side the differential. a bad axle bearing is usually the main reason for noise, when the noise comes on outside of a turn. Then the outside axle bearing is running faster and carrying a greater load than the bearing on the inner axle. Making a turn in the opposite direction will usually reduce or eliminate the noise from a bad axle bearing.
The cause of noise inside the differential can be due to the tight pinion gears, on the pinion shaft, or if there is too much backlash error on these gears. Or the reason can be worn out differential case bearings which can also cause noise on curves. These parts are inside the differential and move relative to each other during turning of the vehicle.
5. Torque steer
Different sizes of tires on the wheels of a drive axle can cause torque steer. This happens in cars which are having unequal length of half shafts, these unequal half shafts make the vehicle to pull to one side during heavy acceleration. Therefore the cars, pull toward one side with the longer half shaft. To prevent this, a single intermediate shaft is used , which allows the use of equal length drive shafts and this helps to equalize the torque to the front two wheels, thus with equal torque on wheels there is no tendency for torque steer..
6. Limited Slip differential problem:
The limited slip differential requires special type of lubricant to be used. The use of wrong lubricant can cause the clutch surfaces to grab. This produces a chattering noise during turns. To remove this problem the lubricant needs to be changed. The lubricant is thus drained out and the special lubricant is added to correct this problem.
7. Use of different size of tires on the vehicle:
The tires of the vehicles hould be of same size, and the air pressure of the tires should also be the same, this also helps to reduce the wear of the car.
8. Broken half shafts:
If any of the half shafts of the vehicle are broken, these need to be replaced.
9. Stripped Splines of the axle shaft.:
If the splines on the axles are stripped, we will have to replace the axle shaft as the reworked splines will not give the desired result.
10. Stripping of the gear teeth:
If the teeth of some gear in the rear axle drive are stripped, these gears needs to be replaced immediately.
11. Fractured taper key at the hub:
Iif the taper key at the hub is fractured, this also needs to be replaced with a new one for better results.