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The vehicles brake system employ hydraulics . This means that a force is transmitted by a liquid. The principle is based on a closed system with pistons, cylinders and a special liquid . How does it work ? Liquids have this very special characteristic they are incompressible unlike air .That is why hydraulic systems must be free of air . Within hydraulic system pressure is exerted on a liquid by means of a force the space within the cylinder is reduced and the liquid is displaced . The resulting pressure acts the same at any point in the system retaining its magnitude. If two cylinders of equal size are connected to each other ,the liquid transmits the exerted force while maintaining the ratio .What does that mean to a vehicle ? The foot exerts a force on the brake pedal. It sets the brake fluid within the brake master cylinder in motion. The liquid is forced through the connected tubing to the wheel brake cylinder, the exerted force is thus transmitted . This principle remains the same even if more then one wheel brake cylinder is connected. The force continues to be transmitted uniformly ,however it is divided into four equal parts proportionally reducing the distance moved by the pistons . In a vehicle this is called a single circuit brake system . For increased safety the system is separated into two circuits. Depending on the vehicle concept , the brake system acts separately on the front and rear axles or in a diagonal direction .  This provides increased safety in case one brake circuit should fail. A hydraulic system not only transmit forces it also multiplies them .For this to happen the operating piston’s diameter must be smaller then that of a working piston . It’s the same in a vehicle the diameter of the brake master cylinder is smaller then that of the wheel brake cylinder .The force exerted by the brake pedal is not only transmitted but also multiplied. The brake system works with a special liquid . To ensure reliable operation it has to meet certain requirements. It should operate equally well at low temperatures as at very high temperatures even if the brakes themselves are operating under extreme heat .That is why the brake fluid must be changed regularly . The fluid is transported via steel pipes in brake hoses from the brake master cylinder to the wheel brakes . For the rear axle brakes the pipes are guided along the under body. Brake hose is used in moveable areas. Additional components like the brake servo allow for comfortable brake operation . For a system such as antilock brake system (ABS) further improves drive, comfort and safety. The rotor attached to the front wheel and the drum attached to the rear wheel rotates along with it when the brakes are not applied . The force generated by the brake pedal is boosted using the vacuum from the engine. The boosting effect causes the brakes to respond even more quickly .The force from the vacuum booster causes the piston inside the master cylinder to move against the spring force and allow the brake fluid to flow under pressure. The pressurized fluid reaches inside the caliper and wheel cylinder . The pressurized fluid reaches inside the caliper , forcing the brake pads inside it to move inwards and against the revolving rotor .The brake pads when comes in contact with the rotor , friction is generated, which reduces the speed of rotor and ultimately stops it completely . The pressurized fluid from the fluid lines reaches the wheel cylinder located inside the brake drum. The pressurized fluid causes the piston inside the wheel cylinder to move outwards . The outward movement of the piston causes the brake pads to move towards the rotating drum. The brake pads rub against the drum, generating friction and converting the kinetic energy into heat energy , and thereby stopping the wheel .