A device for adjusting clearance of a drum brake has an extendable strut assembly having a toothed ring and arranged between first and second shoes cooperating with a braking surface of a drum and moved by an actuating device from a resting position, in which they are distanced from the braking surface, to a braking position, in which they abut against the braking surface. The device has a first lever assembly, a second lever assembly having a coupling portion, and a connecting member having a connecting seat. The coupling portion is coupled to the connecting seat with a predetermined functional clearance. When the first and second shoes move from the resting position, the coupling portion slides in the connecting seat with an idle stroke equal to the predetermined functional clearance without transmitting motion to the connecting member and the first lever assembly. The second lever assembly transmits motion to the connecting member after the coupling portion has covered the idle stroke.

A spreader unit for a drum brake is provided with a readjustment device which ensures that the clearance remains substantially constant even in the case of wear on the brake linings. The readjustment device is arranged between actuating pistons and changes the spacing of the actuating pistons in at least one readjustment step when an actuating travel of the first and second brake shoe holders has exceeded a travel setpoint value. A thermally actuable blocking device mechanically prevents the execution of the readjustment step by the readjustment device at a temperature above a temperature setpoint value

A device for adjusting clearance of a drum brake has an extendable strut assembly having a toothed ring and arranged between first and second shoes cooperating with a braking surface of a drum and moved by an actuating device from a resting position, in which they are distanced from the braking surface, to a braking position, in which they abut against the braking surface. The device has a first lever assembly, a second lever assembly having a coupling portion, and a connecting member having a connecting seat. The coupling portion is coupled to the connecting seat with a predetermined functional clearance. When the first and second shoes move from the resting position, the coupling portion slides in the connecting seat with an idle stroke equal to the predetermined functional clearance without transmitting motion to the connecting member and the first lever assembly. The second lever assembly transmits motion to the connecting member after the coupling portion has covered the idle stroke.

A spreader unit for a drum brake is provided with a readjustment device which ensures that the clearance remains substantially constant even in the case of wear on the brake linings. The readjustment device is arranged between actuating pistons and changes the spacing of the actuating pistons in at least one readjustment step when an actuating travel of the first and second brake shoe holders has exceeded a travel setpoint value. A thermally actuable blocking device mechanically prevents the execution of the readjustment step by the readjustment device at a temperature above a temperature setpoint value.