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BRAKE SYSTEM
The brake system is designed to retard the motion of the car by means of friction. Friction, the resistance between two moving bodies in contact, converts the car's momentum power (kinetic energy) into heat. The amount of pressure exerted by one moving body against the other will determine the amount of friction;the more pressure, the higher the friction; the less pressure, the lower the friction. In the car, this friction is created by the contact between the brake shoe lining and the brake drum surface.
Basically, brake linings are made up of asbestos fibers impregnated with special compounds to bind the fibers together. The most common type of brake lining in the modern car brake system is a molded lining composed of asbestos fibers ground up and pressed into shape. Manufacturers use various lining compounds for specific braking characteristics, such as brass linings added to the asbestos for heavy-duty braking.
In this chapter, you will learn how to detect a faulty power brake system and a faulty or leaking master cylinder or wheel cylinder and calipers, and how to check the condition of the brake shoes or brake friction pads.
Your car's brakes are its primary safety system. Every time you step on the brake pedal, you are calling on your car's brake system to perform a function that is potentially a life-or-death matter. Obviously, this is not the system to tamper with if you do not know what you are doing. If you want to test your basic mechanical ability, pick some other system of your car to begin with. For instance, if you try your own maintenance and repairs on the cooling system and make a mistake, you may have to take a long walk for help, but you will not endanger your safety.
While all the repair procedures given in this chapter should be within the ability of the novice mechanic, you should look over the entire chapter before beginning any brake service job. If you feel the procedures are too complex for you to handle, have your brake serv-ice work done by a professional mechanic.
You will not find any information in this chapter on how to service the hydraulic system of your brakes. There are too many places where a home mechanic can go wrong once he begins to disconnect the parts of this system.
The modern drum brake system
The modern drum brake system, with Bendix servo and self-energizing action, minimizes the amount of pedal pressure necessary to stop the car. This is ac-complished by hooking a spring and adjusting screw between the heel of the primary brake shoe (the lower end of the forward shoe), to the toe of the secondary brake shoe (the lower end of the back shoe).
Since this system uses one spring to anchor both shoes at one end, it allows the other end of both shoes to move freely and simultaneously. When pressure is exerted on the foot brake pedal, fluid in the master cylin-der, hydraulic lines, and wheel cylinder moves the pistons in the wheel cylinder outward. The pistons force the top ends of the brake shoes out against the drum. The forward (primary) shoe tends to lock to the revolv-ing brake drum and tends to turn around with it. As the forward shoe tries to turn with the drum, it pushes the back (secondary) shoe against the drum. The secondary shoe tries to turn with the drum, but it is anchored at the top; so it jams into the drum, locks it, and stops the wheel from turning.
The modern disc brake system
The modern disc brake system uses a heavy disc in place of a drum, and brake friction pads in place of the brake shoes and linings. In place of the wheel cylinder, a caliper is bolted to the wheel spindle so that the friction pads on the caliper can sandwich the disc between them. When pressure is exerted on the brake pedal, the fluid in the caliper moves the pistons, which in turn force the friction pads against the disc, stopping
the car.
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