Drum Brakes are the brake system that some cars have on all four wheels and others just on the rear wheels with disc brakes on the front. They consist of a brake drum which contain two brake shoes and the hydraulic system that includes a cylinder with two pistons.
The brake drum is situated behind each wheel to which it is fitted. Access to the drum is obtained with the removal of the wheel and with the removal of a small retaining screw the drum can be pulled of the centre axle revealing the cylinder and brake shoes.
The Drum Brake is operated through the foot brake, when pressed, hydraulic fluid is forced through piping to the cylinder inside each brake drum. Two pistons inside the cylinder push out horizontally pushing two brake shoes outwards to make contact with the smooth inside of the brake drum.
The drum spins with the wheel and the brake shoes are fixed, when the lining pads on the shoes come into contact with the inside of the drum the spinning speed is reduced according to amount of pressure and time applied to the foot brake.
Periodically the brake shoes will need to be renewed as they have a pad which wears away. If this pad is allowed to wear to thin, rivets holding the pad to the metal shoe will damage the smooth inside of the drum causing damage to the surface reducing the effectiveness of the system, and if the damage is too severe will necessitate replacement of the drum. Another part which, over time fails is the cylinder which through wear and tear between the cylinder and its pistons can cause leakage of hydraulic fluid.