On vehicles with disc brakes, the Brake Caliper is a unit which straddles the brake disc. This unit houses the brake pads, the piston that pushes the two pads onto the disc and on vehicles which use the pads for handbraking, the cable and pushrod mechanism for the handbrake. On some vehicles with rear disc brakes the handbrake has a separate drum, in the centre of the disc, with brake shoes.
The Brake Caliper is positioned behind the wheel and straddles the brake disc,
When the foot brake is pressed the hydraulic system forces the fluid into the cylinder in the caliper which pushes the piston, which in turn pushes the brake pads onto the brake disc.Vehicles using the pads for the handbrake have a cable attached to the caliper which operates a pushrod inside the piston.
As the Brake Caliper houses the cylinder for the piston that pushes the pad onto the brake disc it may be that the cylinder has been damaged causing leakage of hydraulic brake fluid or the seizing of the piston.