The Brake Master Cylinder is the heart of the braking system. It converts the force placed on the pedal into hydraulic pressure. Then, the pressure forces fluid through the brake lines and hoses. For power-assisted brakes, the master cylinder is attached to the Brake Booster. The assembly is mounted on the firewall, in the engine compartment. The brake pedal is linked to the booster. For manual brakes, the master cylinder is attached to the firewall and linked to the pedal.