The drum brake may look complicated, and it can be pretty intimidating when you open one up. Let’s break it down and explain what each piece does.
Like the disc brake, the drum brake has two brake shoes and a piston. But the drum brake also has an adjuster mechanism, an emergency brake mechanism and lots of springs. When you hit the brake pedal, the piston pushes the brake shoes against the drum. When the brake shoes contact the drum, there is a kind of wedging action, which has the effect of pressing the shoes into the drum with more force. The extra braking force provided by the wedging action allows drum brakes to use a smaller piston than disc brakes. But, because of the wedging action, the shoes must be pulled away from the drum when the brakes are released. This is the reason for some of the springs. Other springs help hold the brake shoes in place and return the adjuster arm after it actuates.
What Are Brakes Shoes?
The brake shoe carries the brake lining, which is riveted or glued to the shoe. When the brake is applied, the shoe moves and presses the lining against the inside of the drum. The friction between lining and drum provides the braking effort. Energy is dissipated as heat.
Found in the automotive drum brake assembly, it is a device, actuated by hydraulic pressure, which, through internal pistons, pushes the brake shoes outward against the drum. After a period of time the wheel cylinders will start to leak. When they do the braking force will diminish and, in extreme cases, could cause loss of braking. You probably won’t know something is wrong until you notice the pedal is a lot lower than it used to be, or it slowly sinks as you hold it. If you have your brakes inspected at regular intervals, a leaking wheel cylinder will be caught before it has a chance to ruin your brake shoes.