Self-adjusting drum brake

A Self-adjusting drum brake comprising a support plate on which are slidably mounted two brake shoes carrying friction members adapted to be brought into contact with a rotating drum by a brake motor interposed between two adjacent ends of the shoes, a spacer of variable length interposed between the shoes in the proximity of the brake motor, automatic adjustment means effecting the elongation of the spacer when operation of the brake moves said ends of the shoes apart to an extent exceeding a predetermined operating clearance, and first resilient means urging the shoes against the spacer, characterized by a first shoe carrying by means of a pivot pin a lever against which the brake motor and the spacer normally bear through the action of said first resilient means, second resilient means bearing against the first shoe to apply to the lever a force tending to hold the lever in abutment against the first shoe, a first moment of the force in relation to the pivot pin of the lever being opposite to a second moment of a force exerted on the lever by the brake motor and determining a limit value of said second moment, beyond which value the operation of the brake motor effects the pivoting of a spacer engaging portion of the lever towards the other shoe, thereby neutralizing the automatic adjustment means.