Final Drive

On the Audi 80, the transmission and final drive are located in a common housing, as on almost all front-wheel drive vehicles.

Torque from the engine reaches the final drive through a small pinion gear and a large ring gear. The differential case is bolted to the large ring gear. Inside this case are four meshing bevel gears, two of which are connected to the drive axles.

While the vehicle moves straight, both front wheels rotate at the speed of the final drive ring gear. The differential bevel gears, which rotate at the same speed, do not rotate relative to each other. When turning, the outer wheel must travel a longer distance than the inner wheel. The bevel gears then begin to work: the faster rotation of the outer wheel and its bevel gear acts through both differential pinion bevel gears on the side gear on the inside of the turn, which therefore rotates more slowly.

This compensation is necessary; otherwise the vehicle would move in jerks during turns with the front wheels slipping. However, the differential can also be a disadvantage, for example, if one drive wheel spins on a slippery surface. Then almost no traction is transmitted to the other front wheel, and the vehicle does not move.