A transmission between a driving primary shaft and an outlet shaft of a self-propelled machine, includes a housing within which there are housed, at least in part: a stepdown mechanism; two clutch mechanisms, one being progressive and the other being non-progressive with a movable dog; and a clutch control device including first and second clutch control elements. The second clutch control elements include at least one spring blade extending along the outlet shaft, the spring blade being mounted to move axially on the outlet shaft during axial movement of the dog from the unclutched extreme position towards a clutched position as a result of the movable dog bearing thereagainst, the spring blade being drivable axially on the shaft and being elastically deformable between an active position in which the dog comes into abutment against the spring blade, and an inactive position in which the dog slides along the spring blade.