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7. Vehicle Components

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144
The ABS Brakes System

Anti-lock Braking Systems (ABS) are increasing in popularity and safety. The ABS is a hydro-electric system that sits on top of your conventional braking system. If the ABS should fail, you still have a fully-operational brake system.

The core of the ABS is a computer, which reads individual wheel speed, from sensors at each wheel. If the computer sees a rapid decrease in wheel speed, it translates that to a braking action. If one, or more, wheels apppears to be approaching "zero speed" (lock-up), the computer sends a message to the master cylinder solenoids to rapidly decrease/increse pressure to the affected wheels; in effect, the computer is rapidly "pumping" the brakes for you, up to 20 times per second.

The reason this is necessary is that a tire MUST be moving (rolling) in order to have what is called "rolling friction", which is required for steering. You cannot steer a locked up tire. (This is why skid marks always travel in a straight line, usually towards an object like a tree, telephone pole, or sign...that is what the driver was steering towards when they locked up the brakes). By rapidly pumping the brakes, the tire is allowed to roll, minimally, but enough to permit steering control, thus allowing a driver to escape hitting an offending object.

ABS brakes only work when the brake pedal is depressed, so the guiding principle of ABS is "STOMP, STAY, STEER", meaning stomp down on the pedal, stay on the pedal, and steer while braking.


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Lesson Summary


  

Lesson 7 Quiz


You will now answer 5 questions to test what you learned during this lesson. You must answer all questions correctly to receive completion credit for this lesson. You may answer the questions as many times as necessary to get them right.

You should review the lesson material if you don't do well on the quiz.

  1. The ALTERNATOR:


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  2. This oil warning light means that:


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  3. The minimum tread thickness for passenger car tires is:


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  4. The engine in your car is sometimes called:


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  5. Disc brakes work by:


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