Main gear (Opel Vectra B)

The gearbox and final drive in our Vectra, as in all front-wheel drive cars, are located in a common housing. The flow of power from the engine to the gearbox goes to the final drive through one small and one large gear. The differential housing is bolted to the large gear. This housing contains four nested bevel gears, two of which are connected to the drive shafts.

The differential, also called synchronized transmission, serves to adapt the different distances that the outer and inner wheels travel during a turn. While we are driving in a straight line, both front wheels roll at the speed of the large pinion of the main gear. The bevel gears of the differential housing, rotating at the same speed, remain stationary. When turning, the outer wheel must travel a greater distance than the inner one. Now the bevel gears come into play: the faster rotation of the outer wheel and its bevel gear acts through both transmitting bevel gears on the bevel gear on the inner side of the turn, which rotates correspondingly more slowly. Without this synchronization, the car would drive through the turn jerkily, with the front wheels spinning. On the other hand, the disadvantage of this synchronization is that one drive wheel can spin on a smooth road. Then practically no force is transmitted to the other front wheel, and the car does not move. To repair the differential, it is necessary to dismantle the entire gearbox unit.

(Original source is on the website: OpelBook.ru)