A transmission between a drive element and a drive shaft of the wheels of a self-propelled tractor vehicle includes generally housed at least partially inside a box, a progressive friction clutch that includes at least one rotary driving element and two driven elements that are carried by the drive shaft and are integral in rotation therewith. These driving and driven elements are, under the action of a control element, brought into variable-tightening support contact to obtain a variation of the torque transmitted to the shaft. The drive shaft is formed by two half-shafts mounted to rotate freely relative to one another, each able to be connected, directly or indirectly, to one of the wheels of the vehicle, whereby each of the driven elements is carried by one of the two half-shafts.