Abstract: A clutch unit for the main power take-off of agricultural tractors, having its input shaft (5) aligned with the engine shaft to which it is connected and its coaxial output shaft (6) driving the power take-off (3) via a change-speed gear unit, is positioned behind the rear wheel axle, with the drive hub (61) positioned to the rear of the power take-off change-speed gear unit, so as to be accessible from the outside by removing a cover (13).