Brake Shoes are the friction elements in a drum brake system. When engaged, they apply braking force onto the inside surface of the brake drums to slow the vehicle.
INSTALL LEVEL OF DIFFICULTYDIFFICULT
What are Brake Shoes?
Brake shoes convert your car’s kinetic energy to thermal energy by use of 'friction.” When a brake shoe is heated up in contact with a drum, it starts to transfer small amounts of friction material to the drum. The brake drums (both now with friction material on), will then 'stick' to each other to provide stopping power. The friction of the shoe against the drum is responsible for the majority of stopping power.
How do Brake Shoes Work?
Brake shoes are positioned inside the brake drum and are attached to the backing plate using hold down hardware. Each drum brake assembly consists of a leading and a trailing brake shoe, both actuated at the same time through hydraulic pressure applied by the wheel cylinder. When you apply pressure to the brake pedal, hydraulic fluid is placed under pressure and transfers energy to the wheel cylinder. Pressurized brake fluid pushes the wheel cylinder pistons outward, moving the brake shoes into contact with the inner brake drum surfaces. Brake shoe contact with the drum causes friction, resulting in braking action and reduction of speed. The more pressure applied, the greater the braking force and heat generated.
How are Brake Shoes Made?
Brake shoes utilize a variety of organic and metallic materials to form friction material. These are combined with a binder material that keeps friction material from shedding or breaking under pressure and heat. The friction material is bonded to a metal shoe. The shoe forms the guides for the friction material to precisely fit into brake drum as well as forming the contact surface for the wheel cylinder pistons. Drum brakes are typically found on your car’s rear wheels and often incorporate a mechanical parking/emergency brake mechanism that operates independently of the hydraulic system.
Why do Brake Shoes Fail?
- Brake shoes wear as a normal part of the friction created during braking.
- Brake shoes can wear in an accelerated or asymmetrical fashion if there are problems with the brake pressure in the wheel cylinder, with the hold down or retraction springs, or with the parking brake mechanism.
- Contamination of brake shoe friction material is a common failure mode and occurs when an axle seal leaks gear oil into the drum area, permanently contaminating the brake shoe friction material.
What are Symptoms of Brake Shoe Failure?
- Reduced braking efficiency.
- Contaminated shoes appear to have abnormally dark friction surfaces and a burnt odor. Oil and contamination buildup are typical in this case as opposed to the normal accumulation of brake dust inside the drum assembly.
- Should the parking brake cable bind in the applied position or the parking brake be accidentally left applied while operating the vehicle, the brake shoes will usually appear to be burnt and worn prematurely.
What are Implications of Brake Shoe Failure?
- Severe brake shoe wear will reduce braking efficiency and is extremely dangerous because it decreases stopping distance and predictability.
- Loud squeaking, squealing, or grinding noises during braking.
If you have questions or concerns about brake shoes, your vehicle’s braking system, or any of your vehicle’s components, come into your local Pep Boys where we can answer any question, help you find any part or perform any vehicle service your vehicle may require.