PURPOSE: To dispense with any abrasion adjuster for a brake assembly by attaching a primary brake to a torque transmitting mechanism in the axial direction so as to add its force to a radial friction surface, retarding an input plate, and getting rid of any problem due to a radial stress lying between two brakes.
CONSTITUTION: In order to start a braking operation, a primary braking device 6 is energized whereby a piston 19 and a reaction surface 20 are forcibly pressed to a friction surface 17 in the radial direction of a torque-transmitting mechanism. With this, the rotation of an input plate 9 is delayed to some extent, but since a driven plate 7 is rotated together with a shaft 5. a ball 10 runs on to ramps 11' and 12' by relative angular movements between a pair of pressure plates, and thus the input plate and the driven plate are forcibly pressed in a direction of axially separating from each other. Consequently, lining 14 is forcibly pressed to both brake surfaces 2 and 3, and the input plate further tends to be delayed, and the ball is further pressed, running on to the ramps whereby self-energizing operations are produced there. Since the shaft 5 is not contacted with the input plate 9, a brake is effective by only applying the brake on the driven plate 7.