Drum brakes use the same hydraulic pressure as disc brakes do, but in a different way. A brake "drum" is a round metal hoop similar to looking at the open end of a tuna fish can. The entire braking assembly fits inside this drum. A wheel cylinder is used to transfer the hydraulic pressure into braking. As this cylinder moves, it actuates the brake shoes. The brake shoes are similar in compound to brake pads, but they fit the contour of the inside surface of the drums. As the cylinder expands, it stretches the wheel springs and forces the shoes to contact the inside surface of a drum. This friction then stops the drum and attached wheel.

The drums are usually covered with fins on their outer surfaces to increase cooling. They are not cooled internally, because water could enter through the air vent cooling holes and braking would then be greatly impaired.

Most brake systems are self adjusting for pad or shoe wear. This is accomplished automatically as the car is driven in reverse. The mechanisms compensate for the worn pads or shoes by sensing the contact point and moving slightly outwards.