The friction created when the Volkswagen disc brake caliper pushes the brake pads against the rotors is the action that stops the vehicle. It is this braking component's ability to transform hydraulic pressure to mechanical motion that makes this possible. There is a Volkswagen brake disc caliper on every wheel assembly that utilizes the disc type of braking system. The brake disc caliper is mounted over the rotors in the wheel assemblies on the Volkswagen so pressure can be equally applied to both sides of the rotor. So no damage occurs to the brake disc caliper or the rotors, there are disc brake pads between these braking components. The brake calipers are made out of metal with a seal surrounding the moving piston on its interior. This seal is made of a special polymer so it can withstand the extreme pressures exerted on it from the hydraulic system on the Volkswagen. Over the time period of years that this seal is exposed to that great level of stress, it will eventually crack or split causing a hydraulic fluid leak. This will be evident when driving as the brake pedal becomes soft, or when a puddle of brake fluid is left on the pavement at the wheel when the car is parked. If this auto part is not replaced in a short allotment of time, brake failure will occur on the vehicle. The replacement of the brake disc caliper is just a couple of additional steps more than replacing the brake pads. The hose on the caliper has to be removed. The closed loop hydraulic system on your Volkswagen will also have to be purged of all trapped air that might enter the system during the repair procedure. This will restore the integrity of the braking system on your vehicle.