A SUMMARY OF HOW DRUM BRAKES WORK
Compared to disc brakes, drum brakes are dramatically different in design and
function as illustrated above. The friction media are the brake shoes and drums
(not pads and rotors). Brake shoes are mounted on a backing plate over which
the drum fits. When you apply the brake pedal, brake fluid courses through the
system to the wheel cylinders. These cylinders are small hydraulic actuators that
are bolted to the backing plate, usually at the top of the setup. Small pushrods
are inserted into the ends of the wheel cylinders. When hydraulic fluid is forced
into the cylinders, small pistons within the wheel cylinder press the pushrods
outward against the top of the brake shoes. The brake shoes push out and make
contact with the spinning drum.
This contact creates the friction needed to stop the wheels. When you release
the pedal, the shoes are returned to their rest position by the pressure of the
return springs. Drum brakes have a mechanism that automatically adjusts the
brake shoes every time the brake pedal is depressed with the vehicle in reverse.
This self-adjuster often sticks due to light corrosion or malfunction of the self-
adjusting system and requires periodic manual adjustment of the brakes. It’s a
good idea to have periodic cleaning and adjusting of drum brakes to ensure
dependable and durable operation.