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A. After every four hours of service.
B. After every working day.
C. Once a week.
If your vehicle does not have automatic air tank drains, drain your air tanks at the end of each working day to remove moisture and oil. Otherwise, the brakes could fail.
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A. To release the brakes.
B. To apply the brakes.
C. To test the slack adjusters.
When you push the brake pedal, air is let into each brake chamber. Air pressure pushes the rod out, moving the slack adjuster, thus twisting the brake camshaft. This turns the s-cam forcing the brake shoes away from one another and presses them against the inside of the brake drum.
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A. Reaction distance.
B. Perception distance.
C. Brake lag distance.
With air brakes there is an added delay or Brake Lag. This is the time required for the brakes to work after the brake pedal is pushed. With hydraulic brake, the brakes work instantly. With air brakes it takes a little time, one half second or more, for the air to flow through the lines to the brakes.
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A. Service brake system.
B. Emergency brake system.
C. Parking brake system.
The service brake system applies and releases the brakes when you use the brake pedal during normal driving.
5 / 25
A. Brake hard until the wheels lock, and then get off the brakes for as much time as the wheels were locked.
B. Pump the brake pedal rapidly and lightly.
C. Brake as hard as you can, get off the brakes when the wheels lock, get back on the brakes when the wheels start rolling again.
Stab braking means that you: apply your brakes all the way, and release brakes when wheels lock up. As soon as the wheels start rolling, apply the brakes fully again.
6 / 25
A. 32
B. 23
C. 50
The air brake lag distance at 55 mph on dry pavement adds about 32 feet.
7 / 25
A. Rid the wet tank of alcohol that condenses and sits at the bottom.
B. Eliminate the need for daily tank draining.
C. Reduce the risk of ice in air brake valves in cold weather.
Some air brake systems have an alcohol evaporator to put alcohol into the air system. This helps to reduce the risk of ice in air brake valves and other parts during cold weather. Daily air tank drainage is still needed to get rid of water and oil.
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A. Air pressure
B. Spring pressure
C. Fluid pressure
All trucks, truck tractors, and buses must be equipped with emergency brakes and parking brakes. They must be held on by mechanical force because air pressure can eventually leak away. Spring brakes are usually used to meet these needs.
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A. Depends on the adjustment of the service brakes.
B. Is not affected by the condition of the service brakes.
C. Increases when the service brakes are hot.
The braking power of spring brakes depends on the brakes being in adjustment. If the brakes are not adjusted properly, neither the regular brakes nor the emergency/parking brakes will work right.
10 / 25
A. Remove the keys.
B. Set the parking brakes.
C. Do all of the above.
D. Chock the wheels.
Never leave your vehicle unattended without applying the parking brakes or chocking the wheels. Your vehicle might roll away and cause injury and damage
11 / 25
A. Wet or icy conditions only
B. None
C. All weather conditions
D. Good weather only
Front wheel brakes have been shown to be ideal under all weather and driving conditions. Front wheel braking is unlikely to cause a skid even on icy roads.
12 / 25
A. your brakes may fail because of water freezing.
B. you will drive too quickly.
C. your left side brake will cease to operate.
D. your transmission fluid may drain out.
Compressed air usually has some water and some compressor oil in it, which is bad for the air brake system. For example, the water can freeze in cold weather and cause brake failure.
13 / 25
A. shortens your stopping distance.
B. activates when your wheels are about to lock up.
C. decreases your normal braking capability.
D. increases your normal braking capability.
ABS is a computerized system that keeps your wheels from locking up during hard brake applications.
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A. Excessive use of the service brakes
B. Not relying enough on engine braking
C. Brakes being out of adjustment
D. All of the above
Brakes can fade or fail from excessive heat caused by using them too much and not relying on the engine braking effect. Brake fade is also affected by adjustment.
15 / 25
A. On single vehicles, continue to step on and off the brake pedal until the parking brake valve pops out.
B. All of the above are correct.
C. Continue to step on and off the brake pedal until the manufacturer's low psi specification is met for spring brakes to deploy.
D. On tractor-trailer vehicles, continue to step on and off the brake pedal until the parking brake valve pops out.
On both tractor-trailers and single vehicles, to test whether the spring brakes will come on automatically, use the same method you use for testing the low air pressure warning signal: Step on and off the brake pedal, this time until you reach an even lower psi reading and the parking brake valve closes or pops out.
16 / 25
A. 20
B. 45
C. 60
When the engine is at operating rpms, the pressure should build from 85 to 100 psi within 45 seconds in dual air systems. If the vehicle has larger than minimum air tanks, the buildup time can be longer and still be safe.
17 / 25
A. 150
B. 100
C. 125
The governor controls when the air compressor will pump air into the air storage tanks. When air tank pressure rises to the "cut-out" level around 125 psi, the governor stops the compressor from pumping air. When the tank pressure falls to the "cut-in" pressure around 100 psi, the governor allows the compressor to start pumping again.
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A. the modulating control valve to wear out.
B. the brake linings to split.
C. the brakes to fade.
Brakes can fade or fail from excessive heat caused by using them too much and not relying on the engine braking effect.
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A. expansion of the brake drums.
B. increased contact between the brake drums and the brake linings.
C. improper adjustment of the S-cams.
Brake fade results from excessive heat causing chemical changes in the brake lining, which reduce friction, and also causing expansion of the brake drums.
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A. 75 psi.
B. 125 psi.
C. 150 psi.
Pumping by the air compressor should start at about 100 psi and stop at about 125 psi.
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A. springs.
B. air pressure.
C. bolts and braces.
Parking or emergency brakes must be held on by mechanical force because air pressure can eventually leak away. Spring brakes are usually used to meet these needs. When driving, powerful springs are held back by air pressure.
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A. the air pressure may drop too low during driving.
B. the alcohol evaporator may be low.
C. have the problem fixed after your trip is over.
If air pressure does not build up fast enough, your pressure may drop too low during driving, requiring an emergency stop. Don't drive until you get the problem fixed.
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A. charge the air system and leave the engine running.
B. leave the engine running and release the parking brake.
C. turn off the engine, release the parking brake, and let the system settle.
With a fully-charged air system (typically 125 psi), turn off the engine, release the parking brake (push in); and time the air pressure drop.
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A. natural gas
B. compressed air
C. hydraulic fluid
Air brakes use compressed air to make the brakes work. Air brakes are a good and safe way of stopping large and heavy vehicles, but the brakes must be well maintained and used properly.
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A. compressed air enters the brake chambers.
B. compressed air is released from the brake chambers.
C. compressed air is released from the air tanks.
When you push the brake pedal, air is let into each brake chamber.
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