Why drum brakes?
The drum brake has been around pretty much since cars were invented, and it continues to be used (albeit not as much) because it's cheaper to produce than disc brakes. This is partly because the parking brake can be located inside the drum; a rear disc parking brake entails the use of many more parts.
See how to change your drum brake shoes here
The good bits:
- Drum brakes can provide more braking force than an equal-diameter disc brake.
- They last longer than disc brakes because drums have a larger friction contact area than a disc.
- Drum brakes are cheaper to make than disc brakes, so are cheaper to replace.
- Rear drum brakes generate less heat.
- Wheel cylinders are simpler to recondition than disc brake calipers.
- Brake shoes can be remanufactured for future use.
- Drums have better corrosion resistance than discs.
The not so good bits:
- Excessive heating can occur under heavy braking, which then can cause the drum to distort, which leads to vibration under braking.
- Also under hard braking, the diameter of the drum increases slightly due to thermal expansion, and the brake pedal needs to be pressed farther.
- Brake shoes can overheat to the point where they become glazed.
- Excessive brake drum heating can cause the brake fluid to vaporise.
- Grab is the opposite of fade: when the pad friction goes up, the self-assisting nature of the brakes causes the application force to go up. If the pad friction is increases, the brake will stay engaged due to self-application, even when the external application force is released.
- Drum brakes are relatively complex.
- Maintenance of drum brakes is more time-consuming compared to disc brakes.
Drum brake maintenance
Although drum brakes last longer than disc brakes, it's important to look after them to make sure they continue to perform properly.
Drum return springs that pull the shoes back away from the drums when the brakes are released may be worn, stretched or broken. This causes the brakes to drag. Always replace them instead of trying to repair them.
The hold-down springs that hold the shoes against the backing plates may be corroded. If they break, the debris can jam itself between the shoes and drum, causing the brake to drag or bind.
Brake pedal travel would increase were it not for the adjusters. They are susceptible to corrosion and sticking, though, so replace if they're worn.
Adjuster springs help maintain tension on the adjusters, but lack of use can allow cables to corrode and stick in place, preventing the parking brake from applying or releasing.
A special high-temperature brake lubricant should be used on the drum brake.
