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A. Stay parked without using up service air pressure.
B. Apply more brake pressure if the main tank is getting low.
C. Release the spring brakes to move a short distance.
When main air pressure is lost, the spring brakes come on. Some vehicles have a separate air tank which can be used to release the spring brakes. This is so you can move the vehicle in an emergency.
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A. Worn 1/32 of an inch.
B. Against the drum.
C. Disconnected from the slack adjusters.
D. Worn dangerously thin.
To stop, the brake shoes and linings are pushed against the inside of the drum. This causes friction, which slows the vehicle.
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A. The brake feels spongy when pressure is applied.
B. Pressure on the brake pedal is released and speed increases.
C. You must push harder on the brake pedal to control your speed on a downgrade.
Increasing application pressure to hold the same speed means the brakes are fading.
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A. Is being applied to the brakes.
B. Has been used on the trip.
C. Is in the air tanks.
Application Pressure Gauge shows how much air pressure you are applying to the brakes.
5 / 25
A. The tractor protection valve
B. The one-way check valve
C. The emergency relay valve
Installed on the compressor side of the air tank is a one-way check valve, it allows air into the tanks, but does not allow it to flow back to the compressor.
6 / 25
A. The low boiling point of water reduces braking power.
B. Water can freeze in cold weather and cause brake failure.
C. Water over cools the compressor.
Compressed air usually has some water and some compressor oil in it, which is bad for the air brake system, the water can freeze in cold weather and cause brake failure. The water and oil tend to collect in the bottom of the air tank. Be sure that you drain the air tanks completely.
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A. Air pressure
B. Spring pressure
C. Centrifugal force
When driving, powerful springs are held back by air pressure. If the air pressure is removed, the springs put on the brakes.
8 / 25
A. 1/8
B. 1/4
C. 1/2
Brake drums or discs must not have cracks longer than one half the width of the friction area.
9 / 25
A. 5 psi for single vehicles and 6 psi for combination vehicles.
B. 1 psi for single vehicles and 3 psi for combination vehicles.
C. 3 psi for single vehicles and 4 psi for combination vehicles.
D. 5 psi for single vehicles and 10 psi for combination vehicles.
With a fully-charged air system typically 125 psi, turn off the engine, release the parking brake; and time the air pressure drop. The loss rate should be less than two psi in one minute for single vehicles brakes released and three with the brakes applied, and less than three psi in one minute for combination vehicles with the brakes released and four with the brakes applied.
10 / 25
A. Not applicable; no braking effect is involved in a downgrade.
B. They work as the main braking mechanism.
C. They work as a supplement to the braking effect of your engine.
D. They work as the main braking mechanism with the engine braking effect as an emergency backup.
The use of brakes on a long and/or steep downgrade is only a supplement to the braking effect of the engine.
11 / 25
A. All of the above will work.
B. Accelerate, then brake hard.
C. Use gloves and pull hard on each slack adjuster you can reach.
D. Press the brake pedal while listening for any strange noises.
Use gloves and pull hard on each slack adjuster that you can reach. If a slack adjuster moves more than about one inch where the push rod attaches to it, it probably needs adjustment.
12 / 25
A. applies the brakes in the event of an emergency.
B. lets the air out of the brake chambers.
C. applies the brakes during normal driving.
A parking brake control in the cab allows the driver to let the air out of the spring brakes. This lets the springs put the brakes on.
13 / 25
A. neither of the above will happen.
B. you may lose air pressure, but at least you'll know about it anyway.
C. it may lead to sudden emergency braking in a single-circuit air system.
If the warning signal doesn't work, you could lose air pressure and you would not know it. This could cause sudden emergency braking in a single-circuit air system. In dual systems the stopping distance will be increased. Only limited braking can be done before the spring brakes come on.
14 / 25
A. Either the front or rear brakes will not be fully operational.
B. The emergency brakes will come on immediately.
C. The manual slack adjusters will not be set properly.
A dual air brake system has two separate air brake systems, which use a single set of brake controls. Each system has its own air tanks, hoses, lines, etc. One system typically operates the regular brakes on the rear axle or axles. The other system operates the regular brakes on the front axle and possibly one rear axle.
15 / 25
A. 300 to 350 feet
B. 100 to 250 feet
C. More than 400 feet
The total minimum distance your vehicle has traveled, in ideal conditions; with everything considered, including perception distance, reaction distance and braking distance, until you can bring your vehicle to a complete stop. At 55 mph, your vehicle will travel about 450 feet.
16 / 25
A. foot
B. S-cam
C. emergency
Air brakes are really three different braking systems: service brake, parking brake, and emergency brake.
17 / 25
A. Park on level ground and drain off air pressure before adjusting.
B. Park on level ground, chock the wheels, and release the parking brakes.
C. Stop on level ground and apply the parking brakes.
For manual slack adjustors, the brake pushrod should not move more than one inch, with the brakes released, when pulled by hand.
18 / 25
A. Continue at normal speed and find a garage before the brakes lock.
B. Stop. Safely park and continue only after the system is fixed.
C. Reduce your speed and drive to the nearest garage for repairs.
The warning light and buzzer should come on before the air pressure drops below 60 psi in either system. If this happens while driving, you should stop right away and safely park the vehicle. If one air system is very low on pressure, either the front or the rear brakes will not be operating fully. This means it will take you longer to stop. Bring the vehicle to a safe stop and have the air brakes system fixed.
19 / 25
A. Clean the air filter with alcohol
B. Change the alcohol from a new bottle.
C. Check and fill the alcohol level.
Check the alcohol container and fill up as necessary, every day during cold weather.
20 / 25
A. slack adjuster; tie rod
B. slack adjuster; brake camshaft
C. brake camshaft; tie rod
In S-cam brakes 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. The s-cam forces the brake shoes away from one another and presses them against the inside of the brake drum.
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A. If the brakes are very hot
B. When you are testing whether they will hold the vehicle
C. If you're parking for less than one hour
Don't use the parking brakes if the brakes are very hot (from just having come down a steep grade), or if the brakes are very wet in freezing temperatures. If they are used while they are very hot, they can be damaged by the heat. If they are used in freezing temperatures when the brakes are very wet, they can freeze so the vehicle cannot move. Use wheel chocks instead.
22 / 25
A. Not pressing the brake pedal hard enough
B. Not taking your foot off the accelerator
C. Overheating, low air pressure, and not relying on the engine braking effect
Brakes can fade or fail from excessive heat caused by using them too much and not relying on the engine braking effect, they are also affected by adjustment, and low air pressure.
23 / 25
A. the "stab braking" method.
B. the "controlled braking" method.
C. either of the above.
You should brake in a way that will keep your vehicle in a straight line and allow you to turn if it becomes necessary. You can use the "controlled braking" method or the "stab braking" method.
24 / 25
A. 10 to 15 psi.
B. 20 to 45 psi.
C. 60 to 80 psi.
Tractor and straight truck spring brakes will come fully on when air pressure drops to a range of 20 to 45 psi (typically 20 to 30 psi).
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A. amount of pressure in the brake system.
B. front brakes.
C. spring brakes.
In some vehicles a control handle on the dash board may be used to apply the spring brakes gradually. This is called a modulating valve. It is spring-loaded, so you have a feel for the braking action. The more you move the control lever, the harder the spring brakes come on.
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