The master cylinder is a part of the braking system. It is a cylinder with a reservoir containing hydraulic brake fluid. As pressure builds up when the brake is depressed, the pressurized fluid moves a linkage which moves a piston, and eventually the brakes are engaged. It translates mechanical pressure to hydraulic pressure which engages the brakes. Master cylinders can be used in many systems of a vehicle. Any system that needs to translate mechanical workings into hydraulic workings can accomplish it with a master cylinder. There are at least six other possible applications for master cylinders in a vehicle besides the brakes. But the brake system is the most well known application of a master cylinder. Most master cylinders translate a mechanical signal to another through the medium of the hydraulic system. In the brake system, the mechanical pressing of the brake is turned into the movement of a piston.