The strut, mounted in the vicinity of the brake application mechanism and bearing with each of its ends against each of the shoes (3, 4), has a device which automatially extends according to the wear of the friction components and which consists of a nut-and-bolt system (8-11) operated by a pawl (12) engaging with teeth (11) integral with the nut. The pawl (12) is mounted on an elastic leaf (13) integral with the strut and separated elastically therefrom by a rocker lever (14) which, by tilting, allows the leaf (13) to move toward the strut when the shoes are pushed apart, thus enabling the pawl (12) to cause the nut (11) to rotate and, therefore, the length of the strut to increase. A bimetallic strip (30) is capable of counteracting the tilting movement of the lever (14) when the brake is hot.