A gearbox for a self-propelled machine includes primary and secondary shafts, each having a respective gear train aligned with one another around the shaft. Each gear of the gear train of the primary shaft permanently meshes with a respective gear of the secondary shaft. A gearing mechanism includes a driving member meshing with a driven member for being coupled to/decoupled from the primary shaft by a clutch mechanism. At least one key is engaged selectively with a gear carried by the secondary shaft. The secondary shaft includes two half-shafts mounted freely rotatable relative to each other and aligned by a sleeve inside which one end of each half-shaft is received. The sleeve has at least one longitudinal guide path along which the key, constrained to rotate with the sleeve, is mounted to move axially, this key-holder sleeve being coupled to each of the half-shafts via a respective declutchable coupling.

A differential device (1) for a self-propelled wheeled vehicle, includes an input ring gear (2), two shafts separate from each other, two clutch mechanisms each including a first clutch member (3) mounted integral in rotation to one of the shafts, and a second clutch member (4) mounted freely rotatable relative to the shaft and capable of being rotated by the ring gear (2), the second clutch member being capable of being moved axially. Each second clutch member is provided with elements (44) for bearing contact with the other second clutch member, the elements for bearing contact being capable, in a first given angular configuration of the second clutch members relative to each other, of keeping the second clutch members in the engaged position, and the elements for bearing contact also being capable, in a second given angular configuration, of allowing the second clutch members to shift to the disengaged position.