The main components of the rear axle are:
- main gear, consisting of a pair of bevel gears with helical teeth and hypoid gearing. The meaning of this engagement is that the axes of the driving and driven gears do not intersect. The pinion axle is shifted down by 31.75 mm (at the car VAZ-2101). Thanks to the hypoid meshing of the gears, the main gear is quiet and the ground clearance can be reduced, which, in turn, has a positive effect on the stability of the car;
- differential (pic. 58), with the help of which the axle shafts, when turning the car, are able to rotate at different speeds, resulting in reduced tire wear.
If the wheels rotate at the same speed, then when you turn the car, one of them will slip. Under these conditions, the differential is indispensable. It allows the wheels to rotate at different speeds. On a turn, the inner wheel and gears 1 and 3 of the differential connected to it through the semi-axle travel a shorter distance and rotate more slowly than the outer ones. In turn, the satellites 2 and 4 roll over the slowed down gear 1 and rotate around their axes. In doing so, they impart additional rotational speed to the other differential gear and the outer wheel.
Thanks to the differential, the sum of the revolutions of the rear axle wheels is twice as much as the revolutions of the final drive gear, so if one wheel is stuck, the other begins to rotate at twice the speed. This property is often used by racing drivers.
To reduce the time to complete the turn, the rider abruptly applies the parking brake. At this moment, the axle shafts and wheels rotate at equal speeds, but in different directions, which provides the car with an instant turn.
- axle shafts, which transmit torque directly to the drive wheels;
- rear axle beam, i.e., the body where all the listed nodes are located.
Usually, with proper driving and timely maintenance, the rear axle works reliably for a long time, at least for at least 100 thousand km, and very rarely annoys the driver. A small list of rear axle faults is known.
Their analysis shows that the driver himself is the culprit of most of them.
Increased noise from the rear wheels
The main causes of this defect are: loosening of the rear wheels and wear or destruction of the axle shaft bearing.
Driving with loose wheel bolts can lead to big trouble. Eliminating the defect is not difficult.
With a destroyed or worn half shaft bearing, the situation is more complicated, since the half shaft must be removed.
Until recently, few people dared to remove the axle shaft on their own. The whole difficulty lay in the fact that the axle shaft tightly sits with a bearing in the stocking of the rear axle beam 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 was quickly removed. Currently, this device is commercially available, and the operation of dismantling the axle shaft has become ordinary. Given that the removal and installation of the half shaft bearing is very laborious, shops sell half shafts with a bearing assembly.
If you have established for sure that a particular axle shaft is the source of increased noise, then you don’t even need an inspection ditch to replace it. The procedure for replacing the axle shaft is as follows:
- remove the cap and loosen the wheel 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 the brake shield to the rear axle beam without removing the four bolts so that the brake fastening shield on the flange remains in place;
- using a hammer or other improvised 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 retainer plate, bearing and locking ring;
- insert a new semi-axle assembly into the axle beam and insert its splined end into the hole of the semi-axle gear;
- install the oil deflector, gasket and bearing retainer plate, pre-connected with screws, on four bolts and tighten the fastening nuts;
- install the brake drum and attach it to the axle shaft flange with guide pins;
- install the wheel and tighten the wheel bolts;
- lower the car, after removing the stands;
- tighten the wheel bolts and install the caps.
Constant increased noise during the operation of the rear axle
There are times when you blame the axle shaft, first the right one, then the left one. Both have already been replaced with new ones, and the noise has remained the same. There may be several reasons.
There are simple ones among them, they forgot to pour oil into the gearbox, but there are also very complex ones that cannot be overcome with the help of enthusiasm alone. One of these defects is the deformation of the rear axle beam. What could cause such a malfunction? Usually, careless driving on broken road surfaces. It's good if the speed is low and the shock absorbers are in perfect order. In such conditions, they provide indispensable assistance to the rear axle. If the shock absorbers themselves need to be repaired, then the entire load falls on the springs and the rear axle. The spring is lighter, it can compress. The rear axle beam can only be deformed. There are cases when the axle shafts bend together with the beam. Judge for yourself how, with such a ride, the rear axle does not make noise?
If the rear axle beam is bent, this does not mean that it should be thrown away. In well-equipped service stations, where there is a large measuring plate, a set of prisms and squares, precision measuring instruments and a straightening press, the malfunction may well be eliminated.
Approximately the same tone noise is emitted by the rear axle when the spline connection of the side gears is worn.
Noise during acceleration and engine braking
The noise that occurs during acceleration and braking by the engine indicates that the allowable clearances in the engagement between the gears of the final drive or in the bearings of the drive gear have increased. More often, noise occurs due to increased bearing clearances, which appear if the bearing wears out or the pinion flange fastening nut loosens. It should be remembered that the condition of the drive gear bearing is directly dependent on the tightening torque of the nut. Tighten the flange nut only with a special torque wrench.
The operation must be carried out at a service station.
In order to determine the nature and source of the noise as accurately as possible, it is recommended:
- on a dry horizontal section of the road in calm weather, drive a car with raised door windows at a speed of 20 km / h. Gradually increase the speed and at the same time record the occurrence of new noises at a given speed. Record also at what speed the emerging noises disappear. Accelerate should be up to 100 km / h. When you reach this speed, release the throttle control pedal and, without braking, roll until the car comes to a complete stop, extinguishing the speed with the engine. As with overclocking, note the appearance and decay of noise and the speed at which it occurs. Usually noises appear and disappear at the same speeds both during acceleration and during deceleration;
- after accelerating the car to a speed of 100 km / h, place the gear lever in neutral position and turn off the ignition (make sure that the ignition lock does not work). Let the car coast down to a complete stop, and at this time you record the appearance and attenuation of noises, as in the first experiment. If during the second experiment you found 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 cannot make noise without load.
The noises you heard in the first experiment and absent in the second really come from the main pair, differential or drive gear bearings.
Similarly, it is possible to compare the noises when the engine is running on a stationary car and thereby eliminate the noises of the rear axle, driveline and front suspension.
Noise when cornering
Noises that occur when turning the car, as a rule, come from the differential. A faulty differential responds with noise both to road irregularities and when you sharply press the fuel control pedal at the moment of coasting.
To confirm this assumption, you can use the old method:
- place two stands under the rear axle of the car;
- shift lever to neutral position and rotate one wheel.
The differential can be considered quite serviceable if, at the moment of rotation of one wheel, the second one, without noise and knocking, begins to rotate in the opposite direction. If one of the defects (breakage of satellites, axle gears, wear of the internal surfaces of the differential box) the wheels will rotate in one direction to the accompaniment of noise and rattle.
Oil leak
The traditional defect - oil leakage - does not bypass the rear axle either. Loosening of the bolts securing the gearbox to the beam, wear or damage to the oil seals of the drive gear and axle shafts are possible places where oil can leak from.
The easiest way to deal with a leak that occurs at the beam and gearbox connector. Bolts need to be tightened. For those who are going to perform the operation correctly, that is, using a torque wrench, we remind you: the gearbox mounting bolts are tightened with a torque of 23.5 Nm.
If drops of oil appear in the area of the axle shaft flange, the oil seal will have to be changed. Knowing how to dismantle the axle shaft (described above), it is not difficult to replace the stuffing box, since the stuffing box is located in the flange of the beam.
A failed oil seal is not only the cause of an oil leak. It also contributes to the destruction of the axle shaft bearing. It happens like this: TAd-17I oil is in decline with the rear axle running. Rushing to the flange of the axle shaft and finding a loophole through the oil seal that failed to work, the oil penetrates through the bearing and washes out the grease embedded in it. This mixture of TAd-17I and lubricant enters the brake drum, oiling the surface of the pads along the way and only then flows out.
Usually, after replacing the oil seal, few people check the condition of the axle shaft bearing and the presence of lubricant in it. Very little time passes and it is already 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 motorist who, apparently, having suffered once, developed his own technique:
- with the axle shaft removed, remove the inner (on the gearbox side) bearing shield;
- wash the bearing in gasoline and put Litol-24 grease in a third of the free volume;
- install the axle shaft in its place.
Experience has proven that Litol is reliably stored in the space between the stuffing box and the outer protective washer, thereby providing the bearing with quite good working conditions.
Oil leakage through the gearbox drive gear oil seal is unpleasant because you have to go to a service station. We said above that the drive gear bearing requires very precise adjustment, and in the absence of a special torque wrench and skill, only specialists can perform such adjustment. There are frequent cases when, due to a penny gland, it is necessary to replace more expensive parts.