Both pads are shaped to fit the exact contour of the inside of the drum. So the pads create a lot of friction and force the car or truck to stop quickly. As such, these brakes are not as sensitive or performance minded as front side disc brakes. They are actually rarely used and only provide about Thirty percent of everyday braking power.
While disc brakes consist of a pair of calipers that squeeze brake pads against a rotor disc to cause friction, drum brakes consist of a pair of brake pads that extend outward and press against the inside of what is called the "brake drum." These pads are situated inside the drum. They are mounted on a "back plate," which in turn is attached to the axle and wheel. The cylinder is the part which expands to press the brake shoes outward.
Braking
When the pedal is pressed, brake fluid forces a cylinder on the top and bottom of the brake drum outward. The cylinder has double pistons, one to press on the brake pad on each side. This acts in the inverse way as a muscle does, expanding to cause pressure and push the pads against the drum.
