Brake drumA cast-iron bowl that turns with the wheel. The shoes press on its smooth inside to slow the car.
Backing plateThe fixed plate the whole brake is mounted on. It takes the twisting force of braking and keeps out road dirt.
Wheel cylinderForces the shoes against the drum. Brake fluid from the pedal pushes a piston out of each end.
Primary shoeThe leading shoe, toward the front of the car. The wheel cylinder pushes it against the drum.
Secondary shoeThe trailing shoe, toward the back of the car.
LiningThe friction material on the outside of each shoe. It rubs on the drum and wears away with use.
Return springsPull the shoes back off the drum to their rest position. This happens when the pedal is let go.
Hold-down springsA spring and pin through each shoe. They hold it against the backing plate while letting it move.
Adjuster (star wheel)A threaded rod with a toothed star wheel. Turned a tooth at a time, it lengthens to keep the shoes close to the drum as the linings wear.
Adjusting leverTurns the star wheel on a tooth when the linings have worn. Part of the self-adjuster, it rocks when the brakes work.
Parking brake leverPushes the shoes against the drum without the brake fluid. The parking brake cable pulls it.
How this list was compiled: Read 2026-09-27. (1) US Army, TM 9-8000, Principles of Automotive Vehicles (1985), chapter 34, sections II (brakeshoes, brakedrums, anchor pin, backing plate, primary and secondary shoes, return springs, holddown springs, the star-wheel adjusting screw and self-adjuster) and IV (wheel cylinder, parking brake lever and strut), https://archive.org/details/tm-9-8000-principles-of-automotive-vehicles-1985 . (2) Wikipedia, Drum brake, https://en.wikipedia.org/wiki/Drum_brake : the backing plate (torque plate) that takes the braking torque and keeps out road debris; the cast-iron drum that turns with the wheel; one wheel cylinder with two pistons pushing the shoes; the leading or primary shoe toward the front and the trailing or secondary shoe; the lining; return springs, hold-down hardware, parking brake linkage; the self-adjuster's lever advancing the threaded adjuster gear one tooth at a time. Licence: own work
The drawing: Drawn for this site by script, 2026-09-27. Own work, nothing traced. Licence: own work
How it works
These are the parts of a car's drum brake, the kind still used on many rear wheels. The drum is drawn above, pulled off, and the brake below it as it sits on the backing plate.
Read the full guide
Braking
Brake fluid pushes a piston out of each end of the wheel cylinder. The pistons force the primary and secondary shoes outward, and their lining rubs on the inside of the brake drum. Let go, and the return springs draw the shoes back.
Keeping it adjusted
Hold-down springs keep each shoe against the backing plate. As the lining wears, the adjusting lever turns the adjuster's star wheel a tooth, lengthening it so the shoes stay close to the drum. The parking brake lever works the shoes with a cable instead of fluid.
The primary shoe is the one toward the front of the car; the secondary shoe is toward the back.
Questions and answers
Do drum brakes have pads?
Not usually: they have brake shoes, curved steel shoes with a friction lining that press outward on the inside of the drum. Pads are the flat parts that squeeze a disc brake's rotor.
What is the difference between drum brakes and disc brakes?
A drum brake presses shoes outward against the inside of a drum. A disc brake squeezes pads on both sides of a disc. Disc brakes shed heat faster.
What are the springs in a drum brake for?
Return springs pull the shoes back off the drum when the pedal is let go. Hold-down springs hold each shoe against the backing plate.
What does the star wheel do?
It is the adjuster: a threaded wheel between the shoes' feet. Turning it lengthens the adjuster, keeping the shoes close to the drum as the lining wears.