The typical brake system consists of disc brakes (pictured above) in front and either disc or drum brakes (pictured below) in the rear connected by a system of tubes and hoses that link the brake at each wheel to the master cylinder. Other systems that are
connected with the brake system include the parking brakes, power brake booster and the anti-lock system.
When you step
on the brake pedal, you are actually pushing against a plunger in the master
cylinder, which forces hydraulic oil (brake fluid) through a series of tubes and hoses to the braking unit at
each wheel. Since hydraulic fluid (or any fluid for that matter) cannot be
compressed, pushing fluid through a pipe is just like pushing a steel bar
through a pipe. Unlike a steel bar, however, fluid can be directed through many
twists and turns on its way to its destination, arriving with the exact same
motion and pressure that it started with. It is very important that the fluid
is pure liquid and that there are no air bubbles in it. Air can compress, which
causes a sponginess to the pedal and severely reduced braking efficiency. If
air is suspected, then the system must be bled to remove the air. There are
"bleeder screws" at each wheel cylinder and caliper for this purpose.
On a disc brake , the fluid from the master
cylinder is forced into a caliper where it presses against a piston. The piston,
in-turn, squeezes two brake pads against the disk (rotor), which is attached to the wheel,
forcing it to slow down or stop.
This process is similar to a bicycle brake where two rubber pads
rub against the wheel rim creating friction.
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With drum brakes (below), fluid is forced into the
wheel cylinder, which pushes the brake shoes out so that the friction linings
are pressed against the drum, which is attached to the wheel, causing the wheel
to stop.
In either case, the friction surfaces of the pads on a disk brake system, or the shoes on a drum brake convert the forward motion of
the vehicle into heat. Heat is what causes the friction surfaces (linings) of
the pads and shoes to eventually wear out and require replacement.
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