In the rear final drive of the car are located the final drive with the differential and the electromagnetic coupling.
The final drive is of the hypoid type.
The drive pinion of the final drive is made in one piece with the shaft, the splined end of which is connected to the hub of the control clutch of the electromagnetic coupling.
The drive pinion shaft is installed on two tapered roller bearings.
The outer bearing races are pressed into the seats of the final drive casing, and the inner races are fitted onto the shaft.
Between the inner races a spacer sleeve is installed; when the bearing nut is tightened, the sleeve deforms, ensuring constant bearing preload.
The bearing preload is checked by the turning torque of the drive pinion.
The driven gear of the final drive is secured to the flange of the differential case with bolts.
The differential transmits torque to the rear wheel drives and allows the drives to rotate at different angular speeds.
This allows the wheels, when turning, to travel paths of different lengths without slipping.
The differential case rotates in two tapered roller bearings.
In the differential case are installed two side gears and two pinions, which are in constant mesh.
The pinions rotate around an axle fixed in the differential case.
To the final drive casing the body of the electromagnetic coupling of the all-wheel drive connection is secured with bolts.
The friction electromagnetic coupling plays the role of an inter-axle differential — it redistributes torque between the axles depending on road conditions.
The purpose of the coupling is to redistribute torque from the engine to the rear wheels in accordance with the selected drive mode.
The coupling allows connecting and disconnecting the shaft of the drive pinion of the final drive of the rear final drive with the propeller shaft transmission.
The locking occurs by means of the solenoid (electromagnet).
In 2WD mode no supply voltage is applied to the solenoid, the coupling is unlocked, and torque is not transmitted to the rear wheels.
The transmission works as on a front-wheel-drive car.
In 4WD AUTO mode the locking of the coupling occurs automatically, depending on the difference in rotation of the wheels.
When driving in normal conditions (when the front and rear wheels rotate at the same speed) the coupling is unlocked — all the torque goes to the front wheels.
If the front wheels (or a wheel) begin to rotate faster (to slip), on command of the electronic control unit within 0.1 second supply voltage is applied to the solenoid.
It locks the coupling, and the torque is distributed between the front and rear wheels in the proportion 50/50.
As soon as the grip of all wheels with the road becomes equal again, all the power will again be transmitted to the front wheels.
In 4WD LOCK mode the coupling is constantly locked and the all-wheel drive is constantly engaged.
The electromagnetic coupling connects the rear drive on command from the all-wheel drive control unit.
The driving part of the coupling is connected to the rear propeller shaft, and the driven part — to the shaft of the drive pinion of the final drive.
In the driven part there is a cam mechanism that changes the pressing force.
The current applied to the coupling solenoid causes the connection of the rear axle.
The magnitude of the transmitted torque is regulated by the grip force of the friction discs in the coupling.
At maximum current strength a rigid locking of the coupling occurs.
The final drive is secured on three mounts to the rear suspension subframe.
The bracket with the front mounts is secured to the casing of the rear final drive with two bolts with nuts.
The stud of the final drive cover is inserted into the opening of the rear mount and secured with a nut.
To equalise the pressures outside and inside the rear final drive and the electromagnetic coupling, two breathers serve.
To clean the breather it is necessary to take the breather end piece out of the holder and turn it on the hose.
Possible faults of the final drive and methods of correction
- Cause of the fault — Method of correction
The all-wheel drive does not engage:
- Electrical contact in the wire connector of the electromagnetic coupling is broken or the electrical circuit of the all-wheel drive control system is damaged — Restore the electrical contact in the connector, eliminate the fault of the circuit
- The all-wheel drive control unit is faulty — Replace the electronic unit
- The electromagnetic coupling of the all-wheel drive connection is faulty — Repair the coupling or replace it
Constant increased noise during operation of the rear axle:
- Incorrect adjustment, damage or wear of the gears or bearings of the final drive — Repair the rear axle final drive or replace it
- Wear or incorrect adjustment of the differential bearings — Repair the rear axle final drive or replace it
Noise during acceleration of the car and engine braking:
- Insufficient amount of oil — Restore the oil level and check whether there are leaks in the seals
- Incorrect adjustment of the mesh of the final drive gears — Repair the rear axle final drive
- Incorrect backlash in the mesh of the final drive gears — Repair the final drive
- Increased clearance in the drive pinion bearings due to wear of the bearings — Repair the final drive
Knocking at the beginning of movement of the car:
- Wear of the opening under the pinion axle in the differential case — Repair the rear axle final drive
Oil leakage:
- Wear or damage of the oil seals of the inner joints of the rear wheel drives — Replace the oil seals
- Loosening of the bolts securing the side cover to the casing of the rear axle final drive, damage of the cover gasket — Tighten the bolts, replace the seal
Checking the electromagnetic coupling
When faults are detected in the transmission, the control unit switches to 2WD mode (front-wheel drive), and the warning lamps in the instrument cluster light up.
In this case one can continue driving at low speed to the technical service station.
We carry out the check of the electromagnetic coupling on an inspection pit or a lift.
We disconnect the negative terminal of the battery.
To check the winding of the electromagnetic coupling we remove the connectors of the control wires of the coupling from the plastic holder.
Having pressed on the retainer, we separate them.
We connect the tester probes in ohmmeter mode to the connector.
If the tester shows infinity, it means there is a break in the winding and the coupling must be replaced.
