An automatic adjusting apparatus for a leading and trailing shoe brake is known from the German printed and examined patent application No. 1,505,353. This apparatus includes a looking lever fastened to one of the brake shoes and with a locking pawl interacting with the locking lever and fastened to the same brake shoe. This mechanism cannot, however, be applied to duo-servo brakes because with these brakes the brake shoes must always abut against the supporting lug in their position of rest. Otherwise, there would be the risk that the latter is beaten off, for example, if and when, upon braking during forward driving, a braking operation in reverse movement is initiated. If, however, the supporting lug is missing, the brake shoe may rotate jointly with the drum and any braking effect will no longer be attainable.
Although automatic adjusting apparatus for leading and trailing shoe brakes have been state of the art for years, only adjusting apparatus which are exclusively applicable for service brakes with hydraulic cylinders or manual adjusting apparatus which, moreover, require expensive initial adjustment upon assembly are, as yet, available for duo-servo brakes.