What is the Brake Caliper all about? Most cars come with disc brakes in the front, and many models also have disc brakes in the rear. A caliper is part of the disc brake system. When you press the brake pedal, the brake fluid flows from the master cylinder to the calipers. Brake fluid then applies pressure on the piston inside the caliper, pushing the brake pads against the rotors to slow/stop your car. A car can have either 2 or 4 calipers.