The device (10) is associated to a multidisk clutch (1) for motor vehicles, and allows the automatic disengagement thereof in the deceleration and/or braking initial phase, before that the driver operates the clutch lever (1) for downshifting. The device (10) includes a ramped plate (11) connected to the transmission, which features front cam profiles (110) adapted to actuate oscillating rocker arms (13), arranged inside a drum (5) provided in the clutch (1), when a back torque is generated by the drive wheel of the vehicle, during the deceleration and/or braking step. The rocker arms (13) rotate simultaneously from an inoperative position (N) to an operative position (H), causing the pusher plate (9) to move away with a reduction of the pressure exerted on the sets of friction rings (4, 7), which, therefore, can slip with respect to one another. This avoids abnormal blockages of the rear wheel and improves the drivability and curving of the motor vehicle.