Most modern motorcycles use disc brakes but some still use a drum brake on the rear. Even though drum brakes share common features, details may differ.
Each has a metal drum, usually cast iron, which rotates with the wheel. Within the drum are brake shoes lines with friction material. The brake shoes are moved against the inside of the drum by pistons inside the wheel cylinders. Hydraulic fluid under pressure in the wheel cylinders moves the pistons. Wheel cylinders and brake shoes are mounted onto a metal backing plate which is bolted to the axle or the suspension upright.
The brake drum is a large critical part of the braking system. If the drum is too small or flexible the brake will perform poorly under severe use no matter how good the system may be. The important properties of a good drum brake are:
- Must have a hard wear-resistant rubbing surface and the surface finish must not damage the lining.
- Must be strong enough to withstand the hardest braking at high temperatures.
- Must be stiff and resistant to distortion and warping.
- Must dissipate heat rapidly and withstand excessive temperatures.