A clutch - automatic disengagement device assembly for an engine, clutch and gearbox system of a vehicle, with said clutch including: a basket, in mesh engagement with the crankshaft output, designed to firmly drive in rotation a first set of friction rings, placed within the basket itself; a drum, mechanically connected to the gear shaft, either primary or secondary shaft, arranged coaxially within the basket and provided, in its outer lateral surface, with a toothing, with which a second set of friction rings are engaged, which are interleaved with the rings of said first set; a pressure plate, associated axially to said drum with interposition of spring-loaded members, designed to push the pressure plate to compact and press the pack of the rings (4, 7) of said first and second sets, thus locking them to each other by friction; manually operated control means, designed to act on the pressure plate, against the elastic reaction of said spring-loaded members, to move it away from the aforementioned pack of rings (4, 7) and cause the disengagement of the clutch, said assembly being characterized in that said device comprises: - a ramped plate, interposed between said gear shaft and said drum, locked to the latter with respect to axial translations, but with the possibility of limited angular offsets with respect to the same, due to corresponding studs protruding from said ramped plate and passing through arc-like slots made in the drum; - at least two cam profiles, made in the side of said ramped plate facing the inside of said drum, which define ascending ramps progressively moving away from said side; - at least two rocker arms, arranged inside said drum, pivoted to the latter at their intermediate fulcrums, the opposite ends of each of said rocker arm being intended to contact one of the aforementioned ascending ramps, respectively, and, directly or indirectly, said pressure plate, said rocker arm being adapted to oscillate simultaneously from a non operative position, corresponding to a first angular position of said ramped plate, in which said rocker arms do not interfere with the above mentioned pressure plate, to an operative position, determined due to the angular displacement of said ramped plate with respect to said drum, caused by a back torque generated by the drive wheel of said vehicle in conditions of abrupt deceleration, in which said rocker arms act on said pressure plate to obtain at least partial and progressive automatic disengagement of said clutch. - a ramped plate, interposed between said gear shaft and said drum, locked to the latter with respect to axial translations, but with the possibility of limited angular offsets with respect to the same, due to corresponding studs protruding from said ramped plate and passing through arc-like slots made in the drum; - at least two cam profiles, made in the side of said ramped plate facing the inside of said drum, which define ascending ramps progressively moving away from said side; - at least two rocker arms, arranged inside said drum, pivoted to the latter at their intermediate fulcrums, the opposite ends of each of said rocker arm being intended to contact one of the aforementioned ascending ramps, respectively, and, directly or indirectly, said pressure plate, said rocker arm being adapted to oscillate simultaneously from a non operative position, corresponding to a first angular position of said ramped plate, in which said rocker arms do not interfere with the above mentioned pressure plate, to an operative position, determined due to the angular displacement of said ramped plate with respect to said drum, caused by a back torque generated by the drive wheel of said vehicle in conditions of abrupt deceleration, in which said rocker arms act on said pressure plate to obtain at least partial and progressive automatic disengagement of said clutch.