Abstract: A switching member positioned approximately in the plane of the brake disk has an actuating element therein which is displaceable radially with respect to the brake disk. The element is resiliently held in a rest position and is engageable by adjustable screws mounted on the ends of arms extending from the brake shoe suspension hangers pivotally mounted on each side of the brake disk. The extending arms are spaced with respect to each other in the peripheral direction of the brake disk. The switching member is connected to a fluid pressure source so that when a push button valve in the fluid pressure line is opened, the fluid pressure will be connected through the switching member to the atmosphere when the wear of the brake lining reaches a predetermined low level. The communication to the atmosphere is achieved by displacing the actuating member a sufficient distance so that a radial bore therein provides communication within the switching element between the source of fluid pressure and the atmosphere.