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A. The speed of the air compressor.
B. Air pressure applied to the brakes.
C. When air is pumped into the air tanks.
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. Stop and safely park as soon as possible.
B. Adjust the brake pedal for more travel.
C. Up shift.
When the low air pressure warning light and buzzer first come on, bring the vehicle to a safe stop right away, while you can still control the brakes.
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A. An air use gauge.
B. A supply pressure gauge.
C. At least two brake heaters.
All vehicles with air brakes have a pressure gauge connected to the air tank. If the vehicle has a dual air brake system, there will be a gauge for each half of the system.
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A. Emergency brakes.
B. Foot brakes.
C. S-cam brakes.
Air brakes are really three different braking systems: service brake, parking brake, and emergency brake.
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A. Can steer hard while braking hard.
B. Use the full power of the brakes and lock them.
C. Stay in a straight line and can steer.
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.
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A. 40 psi
B. 60 psi
C. 20 psi
Low air warning devices (buzzer, light, flag) should activate before air pressure drops below 60 psi or level specified by the manufacturer.
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A. Disc brakes
B. S-cam brake
C. Wedge drum
Wedge brakes and disc brakes are less common than s-cam brakes.
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A. Release the brake when you are 5 mph below your "safe" speed.
B. Begin braking when you are 10 mph above your safe speed.
C. Use stab braking.
Snub braking method is used for steep downhill grades, in this method apply the brakes just hard enough to feel a definite slowdown. When your speed has been reduced to approximately five mph below your "safe" speed, release the brakes. When your speed has increased to your "safe" speed, repeat.
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A. A spring-loaded valve that will let you put on the brakes on slowly if the service brakes fail.
B. There is no such thing.
C. Should not be used because it is very unsafe.
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. They work this way, so you can control the spring brakes if the service brakes fail.
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A. You will still have normal brake function and will just need to get the ABS repaired soon.
B. You will have no brake function and your truck will be out of control.
C. It will slow your truck to a halt and force you to pull over.
D. It may cause problems with other mechanical systems and possibly pose a huge fire risk.
Without ABS you still have normal brake functions. Drive and brake as you always have.
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A. You should drive faster so that you will be able to keep the trailer and tractor straight.
B. You should use only the braking necessary to stay safely in control.
C. When you slow down, you should monitor your tractor and trailer and ease off the brakes to keep control.
D. Brake the same way no matter what you're driving: a vehicle with ABS, a vehicle with a trailer, or something else.
When you drive a vehicle with ABS, you should brake as you always have. In other words: use only the braking force necessary to stop safely and stay in control; brake the same way regardless of whether you have ABS on the bus, tractor, the trailer, or both; as you slow down monitor your tractor and trailer and back off the brakes if it is safe to do so to stay in control.
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A. It uses a single set of brake controls.
B. Usually, one system operates the front axle and the other one operates the rear axle.
C. One system is called the "primary" system and the other one is called the "secondary" system.
D. All of the above are true.
Most heavy-duty vehicles use dual air brake systems for safety. A dual air brake system has two separate air brake systems, which use a single set of brake controls. One system or primary system typically operates the regular brakes on the rear axle or axles. The other or secondary system operates the regular brakes on the front axle and possibly one rear axle.
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A. Check if the vehicle was manufactured after 2010.
B. Check if the vehicle was manufactured after 2000.
C. ABS is still optional.
D. Check if the vehicle was manufactured after 1998.
The Department of Transportation requires that ABS be on: air brake vehicles built on or after March 1, 1998.
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A. brakes that come on automatically on a truck or tractor when the psi drops too low.
B. made up of powerful springs that are held back by air pressure while you are driving.
C. not going to take full effect until your psi drops to a certain range, typically 20 to 30 psi.
D. all of the above.
Spring brakes are an important backup system: powerful springs that automatically apply the brakes if they sense that air pressure has been lost for some reason, such as a leak. They will also apply the brakes if the psi gets too low, although ideally, you should take control of your brakes before that happens.
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A. only the parking brakes
B. parts of the service brakes and parking brakes
C. only the service brakes
The emergency brake system uses parts of the service and parking brake systems to stop the vehicle in a brake system failure.
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A. a buildup of brake air pressure.
B. no change in brake air pressure.
C. a loss of brake air pressure.
Each time you release the brakes, some compressed air leaves the system and must be replenished by the air compressor. If you keep pressing and releasing the brake pedal, air may leave the system faster than the air compressor can replenish it, and the air pressure may drop to the point that the brakes won't work.
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A. Only on a slippery road
B. Only when driving downhill
C. Never
Never push the brake pedal down when the spring brakes are on. If you do, the brakes could be damaged by the combined forces of the springs and the air pressure.
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A. you release the brake pedal and your speed increases.
B. you have to press the brake pedal harder than usual to control your speed.
C. the brake feels spongy when you apply pressure.
As the overheated drums expand, the brake shoes and linings have to move farther to contact the drums, and the force of this contact is reduced. So, you will be pressing harder on the pedal.
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A. a white lamp on the right side.
B. a white lamp on the left side.
C. a yellow lamp on the left side.
Converter dollies built on or after March 1, 1998, are required to have antilock brakes. These dollies will have a yellow lamp on the left side of the dolly.
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A. Never do it without downshifting first.
B. Don't lock the wheels for longer than an instant.
C. Disconnecting the steering axle brakes will help keep your vehicle in a straight-line during emergency braking.
Emergency braking does not mean pushing down on the brake pedal as hard as you can. That will only keep the wheels locked up and cause a skid. If the wheels are skidding, you cannot control the vehicle.
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A. lock the wheels for short periods of time.
B. brake in a straight line.
C. can turn sharply.
You apply the brakes as hard as you can without locking the wheels. Keep steering wheel movements very small while doing this. If you need to make a larger steering adjustment or if the wheels lock, release the brakes. Re-apply the brakes as soon as you can.
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A. The brakes could fail.
B. The brakes could heat up.
C. The brakes could lock up.
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.
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A. It is constantly spinning whenever the wheel is spinning.
B. It makes the brake shoes move in an S-shaped path.
C. It is shaped like the letter "S."
The S-cam is S-shaped. 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. stop the vehicle, put it in low gear, depress the brake pedal, and then gently pull against the brakes.
B. brake firmly while slowly moving forward.
C. brake firmly while slowly moving backward.
Pull forward at 5 mph, apply the service brake and stop. Check to see that the vehicle does not pull to either side and that it stops when brake is applied.
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A. If you will be conducting your pre-trip inspection
B. If you will only be away from the truck for a few minutes
C. Never
Never leave your vehicle unattended without applying the parking brakes or chocking the wheels. Your vehicle might roll away and cause injury and damage.
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