drum brakes: how they work and when they need service

plenty of vehicles still use drum brakes on the rear, including a good number of new ones. they are cheaper to build, they work well enough at the back where less braking happens, and they make a simple parking brake.

how they differ from discs

a disc brake squeezes a rotor between two pads. a drum brake pushes two curved shoes outward against the inside of a spinning drum.

drums are enclosed, which keeps grit out but also keeps heat and moisture in. that is why they fade sooner under repeated hard braking and why they are used at the rear, where the load is lighter.

the signs yours need attention

• a scraping or grinding from the rear, particularly when reversing
• the parking brake needing more travel than it used to before it holds
• a pull to one side under braking, from one drum doing more than the other
• a rear brake that drags, or a wheel that gets noticeably hot on a drive
• nothing at all, which is the common one. drums wear slowly and enclosed, so they are usually found during a service rather than noticed

what wears out

the shoes, obviously. but also the wheel cylinder, which pushes them out and which leaks brake fluid as its seals age, and the return springs and adjusters, which seize with rust and leave the brake either dragging or slack.

Ontario road salt is hard on all of it. a drum brake that has never been opened on a ten year old car is usually seized somewhere.

what we do

drums come off, everything gets cleaned and inspected, the adjusters and the hardware get freed or replaced, and the shoes get measured rather than eyeballed.

if the wheel cylinder is weeping, it gets replaced while the brake is open, because doing it later means taking the whole thing apart a second time.