A transmission comprising a shaft (6) made as a single piece or as at least two shaft sections (6A, 6B) on a common axis, a “drive toothed” wheel (5) mounted to rotate freely on said shaft (6), and an automatically clutching clutch mechanism (8) arranged between the drive wheel (5) and the shaft (6) or each of the shaft sections (6A, 6B), the or each clutch mechanism (8) comprising: a clutch plate (81) mounted to rotate freely on the associated shaft (6) or shaft section (6A, 6B)； a part (82) that is carried by and constrained to rotate with the associated shaft (6) or shaft section (6A, 6B)； and a brake of said clutch plate that acts continuously on the angular speed of said plate (81). The brake (83) of the at least one of the clutch plates (81) is threaded on the shaft (6) or the shaft section (6A, 6B) carrying said plate (81).
