The brake calipers are large hydraulic clamps. Calipers have one or more pistons that move outward with increased brake fluid pressure, forcing the friction material (brake pads) to contact the rotor surface. When the driver releases foot pressure from the brake pedal, the caliper piston seal retracts, pulling the brake pads off of the rotor surface. Caliper pistons are self-adjusting, the caliper piston seal maintains proper pad-to-rotor contact as the pads wear. Raybestos re-manufactures calipers. All are leak-tested, coated with rust inhibiting formula, and feature quality o-rings, seals and boots. Caliper integrity is vital to the function of the brake system. Seals, o-rings, slides, and lubrication become compromised as a result of exposure to road grit, corrosion, deposits, heat and contaminated brake fluid. Wheel cylinders are used with drum brake systems. Brake fluid piped to wheel cylinders provides hydraulic pressure to the movable pistons within each cylinder. This pressure forces the brake shoes into the drums. When the driver releases foot pedal pressure, large return springs (hardware) secured to the brake shoes, forces the wheel cylinder pistons back to their resting position.