Automotive Q&A: How Do Drum Brakes Work?
Categories: Brakes · Car Maintenance
Learn how the main components in a drum brake create friction, return to position, and self-adjust as the brake shoes wear.
Brakes
Quick answer
Drum brakes slow a vehicle by pressing brake shoes against the inside of a rotating drum. Hydraulic pressure applies the shoes, return springs release them, and an adjuster helps maintain the correct distance as the shoes wear.
Drum Brakes - How do they Work
Drum brakes are responsible for stopping your vehicle. Drum brakes are usually located on rear wheels because of the need for a parking brake. Parking brakes are added much easier to a drum brake than to a disc brake. Drum brakes contain several different parts: brake shoes, which are used to press against the brake drum and create the necessary friction to stop your vehicle; a backing plate, which basically holds everything together and is attached to the axle; brake drum, which is attached to the wheel; wheel or brake cylinder, which contains the pistons; return springs; and a self-adjusting system that will adjust the position of the brake pad when the brake isn’t applied.
When the brakes are applied, brake fluid forces the pistons to push against the brake shoes, which press against the drum, which will stop the wheel and vehicle. Then, when the brake is released, the return springs send the brake shoes back to their original position. Brake shoes are located very close to the drum so that when you step on your brake pedal, the brakes are immediately applied. Over time, the surface of the brake shoes wears and the position of the shoes must be adjusted so it doesn’t have to travel a farther distance to come into contact with the drum. If the drum brakes didn’t have a self-adjusting system, you would have to press down farther and harder on your brake pedal before the brakes would be applied.
What happens when you press the brake pedal?
Hydraulic pressure builds
Pressing the brake pedal sends pressurized brake fluid toward the wheel cylinder.
The shoes move outward
Pistons in the wheel cylinder push the curved brake shoes toward the drum.
Friction slows the wheel
The shoes contact the rotating drum, converting motion into heat and slowing the vehicle.
The system resets
Return springs pull the shoes back when the pedal is released.
The main parts inside a drum brake
Brake drum
Rotates with the wheel and provides the surface the shoes press against.
Brake shoes
Carry friction material that contacts the inside of the drum.
Wheel cylinder
Uses brake-fluid pressure to move its pistons and apply the shoes.
Return springs
Retract the shoes after braking so the wheel can rotate freely.
Backing plate
Supports the drum-brake hardware and anchors it to the axle assembly.
Adjuster
Maintains proper shoe clearance as the friction material gradually wears.
Signs your brakes should be inspected
A brake pedal that travels farther than usual
Grinding, scraping, or squealing from a wheel
Pulsing, pulling, or shaking while braking
A parking brake that no longer holds securely
A brake warning light or visible fluid leak
A burning odor after repeated or heavy braking
Brake symptoms can have several causes. If braking feels different or unsafe, reduce driving and arrange an inspection promptly.
How to help drum brakes last
Smooth, gradual stops reduce heat and wear. Avoid driving with the parking brake partially applied, pay attention to new noises, and have the brake system inspected at the service interval recommended for your vehicle. Brake-fluid condition and leaks matter too because drum brakes depend on reliable hydraulic pressure.
Do your brakes feel or sound different?
Dallas Tire can inspect the braking system, explain what is worn, and recommend the service your vehicle needs.
Schedule a Brake Inspection