Typical design of a drum brake mechanism
1 - Spring for attaching the shoe to the regulator lever; 2 - Upper tension spring; 3 - Assembling the regulator; 4 - Wheel cylinder; 5 - Regulator lever; 6 - Guide springs; 7 - Anchor pins of guide springs; 8 - Lower tension spring; 9 - Brake shoes; 10 - Parking brake actuator lever
A typical design of a drum brake mechanism is shown in the illustration.
Two shoes equipped with friction linings are installed on a fixed brake shield. The shoes are enclosed inside a drum rotating together with the wheel assembly. The shoes are fixed in their seats by means of springs, which provides them with a certain degree of movement with the possibility of pressing against the working surface of the drum. The shoes are pressed against the drum by the force developed by the pistons of the wheel cylinder when the driver presses the foot brake pedal. By pressing the surface of the friction linings against the walls of the drum, the shoes prevent its rotation, as a result of which the braking process of the vehicle is carried out. When the pressure in the hydraulic tract is weakened, the shoes, due to the force developed by the tension springs, return to their original position, pressing the pistons and releasing the drum.
Modern drum brake mechanisms are equipped with self-regulators that compensate for wear of friction linings. The regulators operate automatically when braking a vehicle moving in reverse.
(The text of the article was taken from the website mitsubishiman.ru)
Note: On some models, the self-regulators are activated every time the car brakes.