There are basically two typed of friction brake in use, namely the drum brake and the disc brake. The drum brake consist of two brake pads or linings which can be forced outwards against the inner surface of a rotating drum fixed to the wheel. The shoes are mounted on a back plate rigidly attached to a non rotating part of the axle. The disc brake consist basically of a pair of callipers that housed friction pads, which are loaded inwards against each people side if a rotating disc, fixed to the wheel.
When the brakes are pressed against the rotating drum or disc, the resulting friction between the pad and the drum or disc slows down the rotating wheels, until they eventually come to a stop. For a motion vehicle , the pushing of the brake lining or pad against the drum or disc is achieved typically BT the system. The system consists of a fluid tank or reservoir, a master cylinder, a system of rigid and flexible connecting pipes, a servo unit and wheel cylinder assemblies. The wheel cylinders operate with shoes and linings or the disc pads. The switch for the light (not shown) , which comes on when braking, is usually fitted at the first junction from the master cylinder.
When the driver presses on the brake pedal, the force applied to the pedal is magnified by a simple linkage mechanism. The force is then transmitted by the hydraulic system through pipelines and flexible hosing to each brake. The above system is referred to as the primary hydraulic braking system.
The primary hydraulic braking system functions properly, provided there is no air in the connecting pipes and the flexible hosing. This is because when air is compressed, it does not transmit the pressures as in the case of brake fluid. Such air must be expelled by bleeding the system. Next time you go to a motor vehicle repair garage, ask the mechanic to show you how a hydraulic braking system is bled.
In case the primary hydraulic braking system fails, a secondary independent system is usually provided for the driver to fall back on. The secondary system is usually referred as handbrake or parking brake. Generally , it used the same pads and linings as the primary system, but the pads and linings are pushed by a mechanical linkage operated by the hand. This works essentially like a bicycle.
