How Drum Brakes Work

With drum brakes, brake fluid is forced into the wheel cylinder which pushes the brake shoes out. This causes the friction linings to be pressed against the drum, which is attached to the wheel, causing the wheel to stop. The friction surfaces on the brake shoes convert the forward motion of the vehicle into heat. Heat is what causes the shoes to eventually wear out.

The main components of a drum brake system are the backing plate, brake shoes, brake drum, and wheel cylinder return springs.

Backing Plate

This attaches to the axle and forms a solid surface for the wheel cylinder, brake shoes.

Brake Shoes

Consisting of a steel shoe with a friction material or lining riveted or bonded to it, the linings eventually wear out and must be replaced. If the linings are allowed to wear through to the bare metal shoe, they will cause severe damage to the brake drum. Brake Drum - Drums are made of iron and have a machined surface on the inside where the shoes make contact. They will show signs of wear as the brake linings seat themselves against the machined surface of the drum. When new shoes are installed, the drum should be machined smooth. Brake drums have a maximum diameter specification that is stamped on the outside of the drum. If the surface cannot be turned within that limit, the drum must be replaced.

Wheel Cylinder

This 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 with a brake shoe. When brake pressure is applied, the pistons are forced out, pushing the shoes into contact with the drum. Wheel cylinders must be replaced if they show signs of leaking.

Return Springs

Return 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 all the way, it will cause premature lining wear because the linings will remain in contact with the drum.

If you have reason to believe that your brakes need attention, our brake experts will be happy to take a look for you.