Rear axle faults (VAZ-2101)

The rear axle of a car is a complex unit with serious adjustments, and therefore most faults can only be eliminated at a service station, and a very well-equipped one at that.

The main components of the rear axle are:

• main gear, consisting of a pair of bevel gears with spiral teeth and hypoid engagement. The meaning of such engagement is that the axes of the driving and driven gears do not intersect. The axis of the driving gear is shifted downwards by 31.75 mm (at the VAZ-2101 car). Thanks to the hypoid engagement of the gears, the main transmission operates silently and the ground clearance can be reduced, which in turn has a positive effect on the stability of the vehicle;
• differential (Fig. 58), with the help of which the axle shafts have the ability to rotate at different speeds when the vehicle turns, resulting in reduced tire wear.

If the wheels rotate at the same speed, then when the car turns, one of them will slip. In these conditions, the differential is irreplaceable. It allows the wheels to rotate at different speeds. When turning, the inner wheel and gears 1 and 3 of the differential connected to it through the axle shaft travel a shorter distance and rotate more slowly than the outer ones. In turn, satellites 2 and 4 roll over gear 1, which has slowed down, and rotate around their axes. In doing so, they impart additional rotation speed to the other differential gear and the outer wheel.



Thanks to the differential, the sum of the rear axle wheel revolutions is twice as large as the revolutions of the main gear pinion, so if one wheel is stuck, the other starts to rotate at double the speed. This property is often used by race car drivers.

To reduce the time it takes to make a turn, the driver abruptly applies the parking brake. At this point, the axle shafts and wheels rotate at equal speeds, but in different directions, which ensures the car makes an instant turn.

• half shafts, which transmit torque directly to the drive wheels;
• rear axle beam, i.e. the body where all the listed units are located.

Usually, with proper driving and timely maintenance, the rear axle works reliably for a long time, at least 100 thousand km, and very rarely bothers the driver. A small list of rear axle faults is known.

An analysis of them shows that the driver himself is the culprit in most of them.

Increased noise from the rear wheels

The main causes of this defect are: loosening of the rear wheel mounts and wear or destruction of the axle bearing.

Driving with loose wheel bolts can lead to big trouble. The defect is easy to fix.

With a damaged or worn axle bearing, the situation is more complicated, since the axle shaft must be removed.

Until recently, few people dared to remove the axle shaft themselves. The whole difficulty was that the axle shaft fits tightly with its bearing in the rear axle beam stocking and, without showing special ingenuity, it was simply impossible to dismantle it. At service stations, there was a special impact device with which the axle shaft could be quickly removed. Currently, this device is available for sale, and the operation of dismantling the axle shaft has become ordinary. Considering that removing and installing the axle shaft bearing is very labor-intensive, stores sell axle shafts with the bearing assembled.


If you have determined that a certain axle shaft is the source of the increased noise, you don't even need a viewing ditch to replace it. The procedure for replacing the axle shaft is as follows:

• remove the cap and loosen the wheel mounting bolts;
• using a jack, raise the rear of the car and install two stands;
• unscrew the mounting bolts and remove the wheel;
• unscrew the guide pins securing the brake drums to the axle shaft and remove the drum;
• unscrew the four nuts securing the axle shaft oil deflector and brake shield to the rear axle beam without removing the four bolts so that the brake mounting shield on the flange remains in place;
• using a striking device or other available means (for example, two bolts that are screwed into horizontally located threaded holes in the flange of the rear axle shaft) press out the axle shaft complete with oil deflector, bearing retaining plate, bearing and retaining ring;
• insert the new axle shaft assembly into the axle beam and insert its splined end into the axle shaft gear hole;
• install the oil deflector, gasket and bearing retainer plate on four bolts, previously connected with screws, and tighten the fastening nuts;
• install the brake drum and secure it to the axle flange with guide pins;
• install the wheel and tighten the wheel mounting bolts;
• lower the car, having first removed the supports;
• tighten the wheel mounting bolts and install the hubcaps.

Constantly increased noise when operating the rear axle

There are cases when you blame the axle shaft, first the right one, then the left one. Both have already been replaced with new ones, but the noise remains the same. There may be several reasons.

Some of them are simple, like forgetting to add oil to the gearbox, but there are also very complex ones that you can't overcome with enthusiasm alone. One of these defects is the deformation of the rear axle beam. What could cause such a malfunction? Usually, careless driving on uneven road surfaces. It's good if the speed is low and the shock absorbers are in perfect order. In such conditions, they provide irreplaceable assistance to the rear axle. If the shock absorbers themselves need repair, then the entire load falls on the springs and the rear axle. It's easier for the spring, it can compress. The rear axle beam can only deform. There are cases when the axle shafts bend along with the beam. Judge for yourself, how can the rear axle not make noise when driving like that?

If the rear axle beam is bent, it does not mean that it should be thrown away. At well-equipped service stations, where there is a large measuring plate, a set of prisms and squares, precise measuring devices and a straightening press, the malfunction can be completely eliminated.

The rear axle makes approximately the same noise in tone when the splined connection of the axle gears wears out.

Noise during acceleration and engine braking

Noise that occurs during acceleration and engine braking indicates that the permissible clearances in the engagement between the main gear pinions or in the pinion bearings have increased. Most often, noise occurs due to increased bearing clearances, which appear if the bearing wears out or the tightening of the pinion flange nut is weakened. It should be remembered that the condition of the pinion bearing is directly dependent on the tightening force of the nut. Tighten the flange nut only with a special torque wrench.

The operation must be performed at a service station.

To determine the nature and source of noise as accurately as possible, it is recommended:

• on a dry horizontal section of the road in windless weather, drive a car with the windows up at a speed of 20 km/h. Gradually increase the speed and simultaneously record the occurrence of new noises at a given speed. Also record the speed at which the noises disappear. You should accelerate to 100 km/h. Having reached this speed, release the gas pedal and, without braking, roll until the car comes to a complete stop, reducing the speed with the engine. Just as when accelerating, record the appearance and attenuation of noises and the speed at which this happens. Usually, noises appear and disappear at the same speeds both during acceleration and deceleration;
• after accelerating the car to a speed of 100 km/h, set the gear shift lever to neutral and turn off the ignition (make sure that the ignition locking device does not operate). Let the car coast to a complete stop, and at this time you record the appearance and attenuation of noise, as in the first experiment. If in the second experiment you detected a noise corresponding to the noise of the first experiment, then know that it does not come from the rear axle gearbox, since the noise occurred during coasting, and gears without a load cannot make noise.

The noises you heard in the first experiment and were absent in the second do indeed come from the main gear, differential, or pinion bearings.

Similarly, it is possible to compare the noise of a running engine with a stationary vehicle and thereby eliminate the noise of the rear axle, driveshaft and front suspension.

Noise when turning

Noises that occur when turning the car usually come from the differential. A faulty differential will make noise both on uneven roads and when the accelerator pedal is pressed sharply while coasting.

To confirm this assumption, you can use the old method:

• place two stands under the rear axle of the car;
• set the gear shift lever to neutral and rotate one wheel.

The differential can be considered to be in good working order if, when one wheel rotates, the other one starts rotating in the opposite direction without noise or knocking. If one of the defects is present, (failure of satellites, axle shaft gears, wear of internal surfaces of differential box) the wheels will rotate in one direction accompanied by noise and grinding.

Oil leak

A traditional defect - oil leakage - does not bypass the rear axle. Loosening of the tightening of the bolts securing the gearbox to the beam, wear or damage to the seals of the drive gear and axle shafts - these are possible places from which oil can leak.

The easiest way to deal with a leak is through the beam and gearbox connector. The bolts need to be tightened. For those who are going to perform the operation correctly, i.e. using a torque wrench, we remind you: the gearbox mounting bolts are tightened to a torque of 23.5 N·m.

If oil drops appear in the area of the axle shaft flange, you will have to change the seal. Knowing how to dismantle the axle shaft (described above), replacing the seal is not difficult, since the seal is located in the beam flange.

A failed seal is not only the cause of oil leakage. It also contributes to the destruction of the axle bearing. This happens approximately like this: TAd-17I oil is in a decrease with the rear axle running. Rushing to the axle flange and finding a loophole through the failed seal, the oil penetrates through the bearing and washes out the grease placed in it. This mixture of TAd-17I and grease gets into the brake drum, along the way it oils the surface of the pads and only then flows out.

Usually, after replacing the seal, few people check the condition of the axle shaft bearing and the presence of grease in it. Very little time passes and it is necessary to change the axle shaft with the bearing assembly.

To prevent this from happening, when replacing the oil seal, use the advice of a Minsk car enthusiast who, apparently having suffered once, developed his own method:

• with the axle shaft removed, remove the inner one (from the gearbox side) bearing protective washer;
• wash the bearing in gasoline and apply Litol-24 grease to a third of the free volume;
• install the axle shaft in its place.

Experience has shown that Litol is reliably retained in the space between the seal and the outer protective washer, thereby providing the bearing with quite good operating conditions.

Oil leakage through the seal of the drive pinion of the gearbox is unpleasant because it requires going to a service station. We said above that the bearing of the drive pinion requires very precise adjustment, and in the absence of a special torque wrench and skill, only specialists can perform such adjustment. There are often cases when more expensive parts have to be replaced because of a cheap seal.