The gearbox used in the classic drive system is a separate unit, enclosed in a separate housing. Such a box usually has three rollers:

■ Input shaft, from the gearbox housing towards the clutch; the clutch disc is mounted at this end of the shaft. This shaft feeds the torque received from the engine into the gearbox.

■ Main shaft, led out of the gearbox housing towards and connected to the propeller shaft. This shaft outputs from the gearbox the torque correspondingly increased by the gear ratio.

■ Intermediate shaft, completely enclosed inside the gearbox housing. This roller acts as an intermediary in the transfer (using pairs of gears) torque between the clutch and main shafts.

The torque received from the engine is input into the gearbox via a clutch shaft, and then driven to the idler shaft through a pair of continuously mesh gears z1 and z2. From this shaft, the drive is transmitted to the main shaft by the appropriate one, coupled depending on the gear, a pair of gears. This is how you get:
Gear I - gears z21 and z31 work together;
Gear II - gears z22 and Z32 work together;
Gear III - direct coupling of the clutch shaft with the main shaft. In this case, neither of the gears is used, so the engine torque is transmitted to the drive shaft. The intermediate shaft turns freely.

Clearance position - none of the gear pairs is engaged between the intermediate and main shafts. The intermediate shaft turns freely, and the clutch and main shafts rotate independently of each other, according to the current rotational speeds of the engine and the drive shaft.

Reverse - requires changing the direction of rotation of the main shaft. So it is necessary to add the reverse gear zR. The z2R gears work together, zR i z31.

In the gearbox, the gear change is achieved by shifting one of the gears. The gear pairs are therefore gears with sliding wheels. Such a gearbox, although structurally the simplest, has many disadvantages, namely: difficult and noisy meshing of gears, causing rapid wear of the edges of the teeth; the necessity to use gears with straight teeth, making noise during operation and the wide spacing of gears on the shafts, increasing the dimensions of the gearbox. Therefore, such gearboxes are not used in modern cars. These disadvantages are not experienced by gearboxes with permanently meshed wheels.