General information about all-wheel drive (Audi A8 D2)

To drive the rear wheels, the vehicle is additionally equipped with a transfer case, cardan shaft, the main rear gear and the rear drive shafts. To equalize the speed of rotation of the front and rear wheels, an interaxle differential is used, which distributes the torque between the front and rear axles of the car. When the wheels of one of the axles of the car slip, the torque transmitted to the other axle is automatically increased. This improves the adhesion of the wheels to the road surface. If the adhesion of the wheels to the road surface decreases, then the torque transmitted to this axle also decreases, as a result of which the stability of the car to lateral skidding increases. Regardless of this, the interaxle differential allows the wheels to rotate at different speeds, which is necessary for the normal operation of the anti-lock braking system.

Torque from the gearbox and final drive is transmitted to the wheels via four drive shafts. Each shaft is inserted into the wheel hub and secured with a nut.

Cardan shaft connects the gearbox to the final drive.

Because cardan shaft is a balanced unit, dirt must not stick to it. When lifting the car for maintenance, it is advisable to clean it cardan shaft and check its technical condition. Whenever cardan shaft removed, to prevent imbalance it should be installed in the same position.

Signs of a faulty driveshaft are usually noise or vibration when the vehicle is moving.

Tightening torques, Nm

Cardan shaft to gearbox	55
Cardan shaft to the main rear gear	55
Suspension of the central part of the propeller shaft to the body	23
Heat shield for cardan shaft to gearbox	23
Cross beam to the body	25
Propeller shaft tunnel to the body	25
Rear cross beam to final drive	55
Rear drive shafts to the main gear:
- bolt M8	40
- bolt M10	77
Parking brake cable retainer	25

[The original source of the article can be found on the website: AudiManual]