Transmission for motor vehicle with manually controlled supplementary underdrive arranged near the differential

The transmission system, comprising a manual-differential gearbox and selectively-engaged supplementary epicycloid step-down gearing between the differential crown gear and housing, has the differential crown gear (18) made with external teeth that mesh with the gearbox driving pinion (7), and internal teeth that mesh with the satellite gears (21) of the epicycloid train. The epicycloid train has a claw coupling system and synchroniser, including a sliding gear which connects the planet gear (25) to the gearbox housing (10) in one position, freeing the epicycloid train, and the planet gear to the satellite carrier formed by the differential housing (24) in a second position, locking the epicycloid train.