Dual secondary shoe drum brake with means preventing depletion of hydraulic cylinder

Hydraulically and mechanically actuable drum brake comprising

• a hydraulic wheel brake cylinder (12) which is fixed to an anchor plate (10) and includes a piston (14),
• a first brake shoe (16) which bears with one end on the wheel brake cylinder (12),
• a second brake shoe (18) which bears with one end on the piston
• an intermediate support (20) on which bear both of those ends (16, 18) of brake shoes which are remote from the wheel brake cylinder (12), and
• a mechanical actuating means (50-58) with which the brake shoes (16, 18) can be moved apart in the vicinity of the wheel brake cylinder (12),
• the wheel brake cylinder (12) and the intermediate support being so arranged that on hydraulic actuation of the brake during forward travel both brake shoes (16, 18) are secondary shoes;
• characterized in that
• the intermediate support (20) comprises a housing (22) which is fixed to the anchor plate (10) ad has a guide (24) at least approximately parallel to the wheel brake cylinder (12) and a stop (26),
• an adjusting member (28) axially displaceable to a limited extent in said guide and
• a push member (34) which with one of its two ends supports the first brake shoe (16) and on hydraulic actuation of the brake is displaceable by a force (c) acting on its second end by said second brake shoe (16) in a direction towards the first brake shoe (16), said push member (34) being connected to the adjusting member (28) in a manner permitting free movement of said push member (34) in the direction of said first shoe (16) while movement in the opposite direction is prevented.