Structure of a drum brake
1. Backing plate
The backing plate (anchor plate) is mounted on the wheel suspension (e.g. steering knuckle, supporting tube). The brake shoes are attached to this so as to be mobile.
2. Hydraulic clamping device
The hydraulic clamping device presses the brake shoes against the brake drum during the braking procedure.
3. Mechanical clamping device
This device is used for the parking function, i.e.: The lever presses the brake shoes against the brake drum when applying the handbrake.
4. Return spring
The return spring draws the brake shoes back from the brake drum after the braking procedure, thereby restoring the clearance.
5. Brake shoes with brake linings
Viewed in the cross section, the brake shoes have a T-shape, this making them more resistant to bending. They are made from either sheet steel welded together or are cast from one piece (cast steel, malleable cast iron). The brake linings are bonded on the backing plate, but can also be riveted. Textar backing plates are correspondingly protected against corrosion.
6. Automatic readjustment
Without this device, too great a clearance would result between the brake lining and brake drum, thus making the pedal travel ever longer. Readjustment is an option for countering this. If the clearance is too great, the readjusting device shifts automatically, e.g. by one tooth. This ensures consistent clearance and/or uniform pedal travel at all times.