it is even possible to realize a negative piston travel while a suitable amount of energy is gained this depends on the angular position of inclined thrust rods 11 and 11 39 and on the distance intermediate pistons 19 and 19 39 may cover within blind end cylindrical bores 21 and 21 39 against the spring force of rings 22 and 22 39 in the circumferential direction during braking when the brake is released a clearance is established by elastic rings 22 and 22 39 on both sides of disc 16 due to the elastic return motion of intermediate pistons 19 and 19 39 thus elastic rings 22 and 22 39 act simultaneously in the manner of a roll back seal in order to avoid that during a braking action in reverse gear i e with brake disc 16 rotating in opposition to the direction of arrow f an effect contrary to the one described hereinabove occurs a preferred improvement of the present invention provides for stops 29 and 29 39 at the end of brake piston 12 and blind end cylindrical device 21 39 close to the disc entry side the stop being in contact with the end of intermediate piston 19 or 19 39 close to the disc entry side under normal braking conditions intermediate pistons 19 and 19 39 are allowed to lift clear of stops 29 and 29 39 in the presence of a braking action in reverse gear however intermediate pistons 19 and 19 39 are in safe engagement with stops 29 and 29 39 thereby effectively preventing an otherwise feared receding motion of intermediate pistons 19 and 19 39 into blind end cylindrical bores 21 and 21 39 it should be understood that the subject of.