Drum brakes incorporate a hydraulic wheel cylinder that presses two opposing brake shoes against a friction surface, simply called a "drum." Retraction of the shoes is spring-actuated once the hydraulic pressure has been released. This style of brake has been substantially replaced by the disk-style brake, as there are inherent problems with the drum system and the relative performance is lacking. The average backyard mechanic can troubleshoot the drum brake system in about 30 minutes.
Access
Drum brakes are hidden behind the wheels, and removing them will allow the brakes to be diagnosed. Turning the lug nuts counterclockwise with the vehicle lifted on a floor jack, remove the wheel. It should be set aside, away from the work area. The floor jack should be joined by a jack stand, for added support.
Disassembly
With the wheel removed, the drum can be pulled directly off on some vehicles; many models will have a small "keeper screw" on the front, to hold it in place when changing the wheel. Turning the keeper screw counterclockwise will allow the drum to slide off of the brake assembly. With the drum off, the shoes, wheel cylinder, adjustment bolt and springs can all be inspected.
Inspection
The drum itself should be free of debris, while some dust is normal. The shoes should have adequate material on them and should not be wet or shiny. Shiny shoes could mean that they have been maladjusted or have been used heavily and become heat damaged. The wheel cylinder should have no leaks, and the rubber seals on either side should be clean and soft. Damage to these seals will cause the fluid to leak, and the pedal will be soft or not apply the brakes at all. The springs that retract the shoes should be attached and clean, without excessive rust. Work springs can cause "dragging" or the shoes not retracting fully. The brake fluid, checked at the master cylinder, should be clean and golden yellow. Black or dirty brake fluid could indicate heat damage, or contaminated fluid. The adjustment bolt is usually at the bottom of most drum brake assemblies and should have very little play when the brakes are not applied. Turning it clockwise will tighten the brake shoes.
