In an air braking system, the three most common types of foundation brakes are S-cam drum brakes, disc brakes, and wedge brakes. Components of S-cam drum brakes include include brake drums, brake shoes and linings, camshafts, pushrods, cam support brackets, spiders, rollers, return springs, dust shields and backing plates, slack adjusters and brake chambers. In an S-cam drum brake, the brake shoes are mounted to the brake spider. Components of disc air brakes include rotors, calipers, brake pads, slack adjusters and brake chambers.