Vehicle brakes

Claim 1

An internal shoe drum brake including a pair of brake shoes which can be expanded, against the action of shoe return spring means, alternatively by power actuated service brake means or by manually actuated auxiliary brake means, a strut of adjustable length which transmits manually applied loads between the shoes but is relieved of load upon actuation of the service brake means, the strut comprising a pair of relatively rotatably members screw-threaded togEther, and pawl and ratchet means for effecting relative rotation of the members to lengthen the strut in response to excess travel of the brake shoes upon brake actuation, wherein such relative rotation is effected only when the service brake is operated to relieve the load imposed on the strut by the return spring means, wherein a pawl spring in the form of a coil spring pre-stressed in torsion and in compression acts on the pawl on the one hand to bias it to rotate in a sense to increase the length of the strut and on the other hand to urge the pawl laterally into engagement with the ratchet, the rotational force applied to the pawl by the spring being intermediate the force required to overcome the frictional resistance to rotation of the strut parts when the strut is subjected to load by the shoe return springs and the force required to effect such rotation when the shoe return spring load is relieved by service brake actuation.