The Ford Focus brake system uses a front pad and caliper system with disc brakes while the rear is a shoe and drums system. The drums can crack and wear over time with heavy use. The heat generated during the braking process can glaze the drums as well. If your drums have damage to them, you can replace them with new drums, which are available at any auto parts store or though a Ford dealership.
Loosen the rear lug nuts on your Focus with a lug wrench, but do not remove them from the wheel studs yet. The wheels will become unstable if you take the lug nuts off while there is still weight on the wheels.
Position a jack under the rear suspension of the car and lift it off the ground. Place a set of jack stands under it and lower the car onto the stands to support it. Remove the lug nuts from the wheel studs, then remove the wheels.
Examine the area around the wheel studs where they come through the brake drum. If the drums have never been off the car, there may be several metal clips on the wheel studs. These were used to retain the drums during assembly. Use a flat screwdriver to pry the clips off the studs. Discard the clips.
Grasp the sides of the brake drum and pull it back toward you. It should slide right off the brake shoes and wheel studs. Move to the opposite side of the car and repeat the process, removing the second drum if necessary.