The working principle of this system, which has names like brake fluid, is quite simple. As soon as you press the brake, the piston moves and the calipers close with the pressure of the oil inside the hydraulic mechanism. As soon as the calipers close, the brake pads and wheel discs stick together. So your car slows down or stops. However, it is important to remember that the vehicle cannot brake in the event of hydraulic fluid or oil draining.