Free CDL Air Brakes Practice Test 2019

QUESTION NO: 1
In newer vehicles with air brakes, you put on the parking brakes using a __________-shaped, yellow, push-pull control knob.

A. round
B. diamond
C. octagon
D. oval

Answer: B

Explanation:

In newer vehicles with air brakes, you put on the parking brakes using a diamond-shaped, yellow, push-pull control knob. You pull the knob out to put the parking brakes (spring brakes) on, and push it in to release them. On older vehicles, the parking brakes may be controlled by a lever. Use the parking brakes whenever you park.

QUESTION NO: 2
Wedge brakes __________

A. are self-adjusting.
B. require manual adjustment.
C. do not require adjustment.
D. either A or B

Answer: D

Explanation:

With wedge brakes, the brake chamber push rod pushes a wedge directly between the ends of two brake shoes. This shoves them apart and against the inside of the brake drum. Wedge brakes may have a single brake chamber, or two brake chambers, pushing wedges in at both ends of the brake shoes. Wedge type brakes may be self-adjusting or may require manual adjustment. Wedge brakes are less common than s-cam brakes.

QUESTION NO: 3
The parking brake system __________

A. uses parts of the service and parking brake systems to stop the vehicle in the event of a brake system failure.
B. applies and releases the parking brakes when you use the parking brake control.
C. applies and releases the brakes when you use the brake pedal during normal driving.
D. none of the above

Answer: B

Explanation:

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. Air brakes are really three different braking systems: service brake, parking brake, and emergency brake. The parking brake system applies and releases the parking brakes when you use the parking brake control.

QUESTION NO: 4
When you are testing the air leakage rate, you should apply __________ psi or more with the brake pedal after the initial air drop.

A. 80
B. 90
C. 100
D. none of the above

Answer: B

Explanation:

If you drive a vehicle with air brakes, you should conduct a final air brake check instead of a hydraulic brake check during step seven of the Seven-step Inspection Method. Test the air leakage rate. 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 and less than three psi in one minute for combination vehicles. Then apply 90 psi or more with the brake pedal. After the initial pressure drop, if the air pressure falls more than three psi in one minute for single vehicles (more than four psi for combination vehicles), the air loss rate is too much. Check for air leaks and fix the problem before driving the vehicle. Otherwise, you could lose your brakes while driving.

QUESTION NO: 5
Which of the following statements is true?

A. When only the tractor has ABS, you should be able to maintain steering control, but there is greater risk of jackknifing.
B. Having ABS on only the tractor, only the trailer, or even on only one axle, still gives you more control over the vehicle during braking.
C. When only the trailer has ABS, the trailer is more likely to swing out.
D. all of the above

Answer: B

Explanation:

When you brake hard on slippery surfaces in a vehicle without ABS, your wheels may lock up. When your steering wheels lock up, you lose steering control. When your other wheels lock up, you may skid, jackknife, or even spin the vehicle. ABS helps you avoid wheel lock up. The computer senses impending lockup, reduces the braking pressure to a safe level, and you maintain control. You may or may not be able to stop faster with ABS, but you should be able to steer around an obstacle while braking, and avoid skids caused by over braking. Having ABS on only the tractor, only the trailer, or even on only one axle, still gives you more control over the vehicle during braking. Brake normally. When only the tractor has ABS, you should be able to maintain steering control, and there is less chance of jackknifing. But, keep your eye on the trailer and let up on the brakes (if you can safely do so) if it begins to swing out. When only the trailer has ABS, the trailer is less likely to swing out, but if you lose steering control or start a tractor jackknife, let up on the brakes (if you can safely do so) until you gain control. When you drive a tractor-trailer combination 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 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. There is only one exception to this procedure, if you always drive a straight truck or combination with working ABS on all axles, in an emergency stop, you can fully apply the brakes. Without ABS, you still have normal brake functions. Drive and brake as you always have. Remember, if your ABS malfunctions, you still have regular brakes. Drive normally, but get the system serviced soon.

QUESTION NO: 6
A fully-charged air system is typically around __________ psi.

A. 100
B. 105
C. 110
D. none of the above

Answer: D

Explanation:

If you drive a vehicle with air brakes, you should conduct a final air brake check instead of a hydraulic brake check during step seven of the Seven-step Inspection Method. Test the air leakage rate. 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 and less than three psi in one minute for combination vehicles. Then apply 90 psi or more with the brake pedal. After the initial pressure drop, if the air pressure falls more than three psi in one minute for single vehicles (more than four psi for combination vehicles), the air loss rate is too much. Check for air leaks and fix the problem before driving the vehicle. Otherwise, you could lose your brakes while driving.

QUESTION NO: 7
Emergency brakes and parking brakes are usually held on by ___________ brakes, because air pressure can eventually leak away.

A. s-cam
B. wedge
C. disc
D. spring

Answer: D

Explanation:

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. When driving, powerful springs are held back by air pressure. If the air pressure is removed, the springs put on the brakes. 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. A leak in the air brake system which causes all the air to be lost will also cause the springs to put on the brakes.

QUESTION NO: 8
If spring brakes are not adjusted properly, the __________

A. regular brakes will not work correctly.
B. emergency/parking brakes will not work correctly.
C. both A and B
D. none of the above

Answer: C

Explanation:

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). Do not wait for the brakes to come on automatically. 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. 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.

QUESTION NO: 9
With air brakes, releasing the brakes lets some compressed air __________

A. into the system, so the air pressure in the tanks is increased.
B. into the system, so the air pressure in the tanks is reduced.
C. out of the system, so the air pressure in the tanks is increased.
D. out of the system, so the air pressure in the tanks is reduced.

Answer: D

Explanation:

You put on the brakes by pushing down the brake pedal. (It is also called the foot valve or treadle valve.) Pushing the pedal down harder applies more air pressure. Letting up on the brake pedal reduces the air pressure and releases the brakes. Releasing the brakes lets some compressed air go out of the system, so the air pressure in the tanks is reduced. It must be made up by the air compressor. Pressing and releasing the pedal unnecessarily can let air out faster than the compressor can replace it. If the pressure gets too low, the brakes won’t work.

QUESTION NO: 10
ABS __________

A. reduces braking pressure to a safe level.
B. senses impending wheel lockup.
C. helps you maintain control of the vehicle.
D. all of the above

Answer: D

Explanation:

When you brake hard on slippery surfaces in a vehicle without ABS, your wheels may lock up. When your steering wheels lock up, you lose steering control. When your other wheels lock up, you may skid, jackknife, or even spin the vehicle. ABS helps you avoid wheel lock up. The computer senses impending lockup, reduces the braking pressure to a safe level, and you maintain control. You may or may not be able to stop faster with ABS, but you should be able to steer around an obstacle while braking, and avoid skids caused by over braking. Having ABS on only the tractor, only the trailer, or even on only one axle, still gives you more control over the vehicle during braking. Brake normally. When only the tractor has ABS, you should be able to maintain steering control, and there is less chance of jackknifing. But, keep your eye on the trailer and let up on the brakes (if you can safely do so) if it begins to swing out. When only the trailer has ABS, the trailer is less likely to swing out, but if you lose steering control or start a tractor jackknife, let up on the brakes (if you can safely do so) until you gain control. When you drive a tractor-trailer combination 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 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. There is only one exception to this procedure, if you always drive a straight truck or combination with working ABS on all axles, in an emergency stop, you can fully apply the brakes. Without ABS, you still have normal brake functions. Drive and brake as you always have. Remember, if your ABS malfunctions, you still have regular brakes. Drive normally, but get the system serviced soon.

QUESTION NO: 11
During step seven of the Seven-step Inspection Method, check the __________

A. condition and tightness of the air compressor drive belt (if the compressor is belt driven).
B. slack adjusters on s-cam brakes.
C. rate of air pressure buildup.
D. brake drums (or discs), linings and hoses.

Answer: C

Explanation:

If you drive a vehicle with air brakes, you should conduct a final air brake check instead of a hydraulic brake check during step seven of the Seven-step Inspection Method. Check the rate of air pressure buildup. 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. Check the manufacturer’s specifications.) In single air systems (pre-1975), typical requirements are pressure buildup from 50 to 90 psi within three minutes with the engine at an idle speed of 600-900 rpms. 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.

QUESTION NO: 12
Front brake limiting valves are on some vehicles made before __________

A. 1970
B. 1975
C. 1980
D. 1985

Answer: B

Explanation:

Some older vehicles (made before 1975) have a front brake limiting valve and a control in the cab. The control is usually marked “normal” and “slippery.” When you put the control in the “slippery” position, the limiting valve cuts the “normal” air pressure to the front brakes by half. Limiting valves were used to reduce the chance of the front wheels skidding on slippery surfaces. However, they actually reduce the stopping power of the vehicle. Front wheel braking is good under all conditions. Tests have shown that front wheel skids from braking are not likely even on ice. Make sure the control is in the “normal” position to have normal stopping power.

QUESTION NO: 13
To __________, turn off the engine when the air system is fully charged, release the parking brake, and time the air pressure drop.

A. test the low pressure warning signal
B. check the rate of air pressure buildup
C. test the air leakage rate
D. none of the above

Answer: C

Explanation:

If you drive a vehicle with air brakes, you should conduct a final air brake check instead of a hydraulic brake check during step seven of the Seven-step Inspection Method. Test the air leakage rate. 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 and less than three psi in one minute for combination vehicles. Then apply 90 psi or more with the brake pedal. After the initial pressure drop, if the air pressure falls more than three psi in one minute for single vehicles (more than four psi for combination vehicles), the air loss rate is too much. Check for air leaks and fix the problem before driving the vehicle. Otherwise, you could lose your brakes while driving.

QUESTION NO: 14
If you are driving on a long and/or steep downgrade and your “safe” speed is 40 mph, you should apply the brakes at 40 mph and release them at __________ mph.

A. 35
B. 30
C. 25
D. 20

Answer: A

Explanation:

Remember. The use of brakes on a long and/or steep downgrade is only a supplement to the braking effect of the engine. Once the vehicle is in the proper low gear, the following is the proper braking technique. 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. (This brake application should last for about three seconds.) When your speed has increased to your “safe” speed, repeat steps one and two. For example, if your “safe” speed is 40 mph, you would not apply the brakes until your speed reaches 40 mph. You now apply the brakes hard enough to gradually reduce your speed to 35 mph and then release the brakes. Repeat this as often as necessary until you have reached the end of the downgrade.

QUESTION NO: 15
Hitting the brakes if someone suddenly pulls out in front of you is a good response if __________

A. there is enough distance to stop.
B. you use the brakes correctly.
C. both A and B
D. neither A nor B

Answer: C

Explanation:

If someone suddenly pulls out in front of you, your natural response is to hit the brakes. This is a good response if there is enough distance to stop and you use the brakes correctly. 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.

QUESTION NO: 16
With s-cam brakes, air pressure pushes the __________ out, moving the __________, thus twisting the __________

A. rod, slack adjuster, brake cam shaft.
B. slack adjuster, brake cam shaft, rod.
C. brake cam shaft, rod, slack adjuster.
D. none of the above

Answer: A

Explanation:

With 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 cam shaft. This turns the s-cam (so called because it is shaped like the letter “S”). The s-cam forces the brake shoes away from one another and presses them against the inside of the brake drum. When you release the brake pedal, the s-cam rotates back and a spring pulls the brake shoes away from the drum, letting the wheels roll freely again.

QUESTION NO: 17
Brake drums or discs must not have cracks longer than __________ the width of the friction area.

A. one-fourth
B. one-half
C. three-fourths
D. none of the above

Answer: B

Explanation:

During step five of the Seven-step Inspection Method, you will conduct a walkaround inspection. If you drive a vehicle with air brakes, you should also check the brake drums (or discs), linings and hoses during this step. Brake drums (or discs) must not have cracks longer than one half the width of the friction area. Linings (friction material) must not be loose or soaked with oil or grease. They must not be dangerously thin. Mechanical parts must be in place, not broken or missing. Check the air hoses connected to the brake chambers to make sure they aren’t cut or worn due to rubbing.

QUESTION NO: 18
If you are driving a vehicle with air brakes, you must test the air leakage rate during step __________ of the basic Seven-step Vehicle Inspection.

A. two
B. five
C. seven
D. none of the above

Answer: C

Explanation:

If you drive a vehicle with air brakes, you should conduct a final air brake check instead of a hydraulic brake check during step seven of the Seven-step Inspection Method. Test the air leakage rate. 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 and less than three psi in one minute for combination vehicles. Then apply 90 psi or more with the brake pedal. After the initial pressure drop, if the air pressure falls more than three psi in one minute for single vehicles (more than four psi for combination vehicles), the air loss rate is too much. Check for air leaks and fix the problem before driving the vehicle. Otherwise, you could lose your brakes while driving.

QUESTION NO: 19
If you are driving a vehicle with a front brake limiting valve and a control in the cab, make sure the control is in the __________ position.

A. slippery
B. normal
C. off
D. none of the above

Answer: B

Explanation:

Some older vehicles (made before 1975) have a front brake limiting valve and a control in the cab. The control is usually marked “normal” and “slippery.” When you put the control in the “slippery” position, the limiting valve cuts the “normal” air pressure to the front brakes by half. Limiting valves were used to reduce the chance of the front wheels skidding on slippery surfaces. However, they actually reduce the stopping power of the vehicle. Front wheel braking is good under all conditions. Tests have shown that front wheel skids from braking are not likely even on ice. Make sure the control is in the “normal” position to have normal stopping power.

QUESTION NO: 20
The cut-out level for air tank pressure is around __________ psi.

A. 100
B. 125
C. 150
D. 175

Answer: B

Explanation:

The air compressor 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 pounds per square inch, or “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.

QUESTION NO: 21
Air storage tanks are equipped with drain valves __________

A. at the top.
B. on the right side.
C. on the left side.
D. at the bottom.

Answer: D

Explanation:

Compressed air usually has some water and some compressor oil in it which is bad for the air brake system. For example, 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. Each air tank is equipped with a drain valve in the bottom. There are two types. The first type is manually operated by turning a quarter turn or by pulling a cable. You must drain the tanks yourself at the end of each day of driving. The second type is automatic. The water and oil are automatically expelled. These air tanks may be equipped for manual draining as well. Automatic air tanks are available with electric heating devices, which help prevent freezing of the automatic drain in cold weather.