Light Vehicles`Drum Brake System

Light Vehicles`Drum Brake System

Light Vehicles`Drum Brake System is used on rear axle of the vehicle. Drum brakes consist of a backing plate, brake drum, brake shoes, brake linings, wheel cylinder, springs and a self adjusting system. Brake linings are riveted to the brake shoes and then mounted on to the backing plate. Brake drum is placed on the wheel.

When the brakes are applied, brake fluid is forced under the pressure into the wheel cylinder which in turn causes the pistons to push the brake shoes in to contact with the drum and creates friction because of which the wheels start to slow down and stop. As the brake linings wear, the shoes must travel a greater distance to reach the drum. In this situation, a self adjusting mechanism reacts by adjusting the rest position of the shoes.

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drum brake system


Brake shoes are made of iron and the linings are riveted to them. When the linings eventually wear out, they must be replaced. If the linings are allowed to wear through to the metal shoes, they will cause damage to the brake drum.


The backing plate is attached to the axle and forms a solid surface for the wheel cylinder, brake shoes and other parts.


Brake drums are made of iron and have a machined surface on the inside. Just as other parts, brake drums will show signs of wear. When new shoes are installed, the brake drums should be machined smooth. However, brake drums have a maximum diameter specification which is stamped on the outside of drum. When a drum is machined,  it must never exceed that measurement. If the surface can not be machined within the limit, it must be replaced.


The wheel cylinder consists of a cylinder that has two pistons. one on each side. Each piston has a rubber seal and a shaft that connects the piston to the brake shoe.  When pressure is applied, the pistons are forced out pushing the shoes into contact with the drum. Wheel cylinders must be repaired or replaced if they show signs of leaking.


Springs pull the brake shoes back to their rest position after the pressure is released from the wheel cylinder. If the springs are weak and do not return the shoes, they will cause premature lining wear. Replacement is recommended in the case they show signs of fatigue.


The parts of a self adjusting system should be cleaned and lubricated to ensure that the brakes maintain their adjustment over the life of the linings. If the self adjuster stops working, you will have to step down further and further on the brake pedal before the brakes begin to engage and this in turn affects the braking system safety.

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