Abstract: A pair of axially aligned input and output shafts are jornalled from a frame supporting a brake drum about the output shaft and the output shaft mounts two pairs of diametrically opposite brake shoes therefrom spring biased into friction braking relation with the inner surfaces of the drum. One pair of brake shoes are of the self-energizing type to brake the output shaft against rotation in one direction relative to the drum and the other pair of shoes are of the self-energizing type for frictionally braking the shaft against rotation in the other direction relative to the drum. Connecting structure is provided establishing a limited loss motion connection between the shafts and includes control structure to release one pair of the brake shoes responsive to torque input to the input shaft above a predetermined minimum in the first direction and to release the other pair of brake shoes responsive to an equal amount of torque input to the input shaft in the opposite direction.