force through the sealing unit 16 is forced against the conical lug 19 of the nut 15 thereby causing the nut to rotate the nut rotates until the friction force in the friction cone 20 has increased to such an extent that a further rotation is prevented this will terminate the readjustment and restore the initial situation for the succeeding braking operation now the operations occurring with the mechanical application of the brake parking brake will be described by rotating the actuating shaft 6 the push member 7 is forced onto the shaft 39 of the spindle 14 with the spindle in fig1 being moved to the left until the clearance of the thread 29 has been closed the spindle 14 is forced onto the nut 15 thereby forcing the conical lug 19 against the friction face of the piston 9 the friction cone 20 already initially closed as described above is sealed even more firmly further movement of the spindle 14 to the left will exert pressure on the piston thereby moving the piston in the same direction against the pad and brake disc the thread driving torque tending to rotate the nut in view of the force exerted on the spindle will be overcome by the friction torque of the friction cone 20 i e the nut is unable to rotate despite the clamping force of the mechanical actuator 3 hence no adjustment will be possible during the mechanical.