Air Brakes CDL Practice Test

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Air Brake Endorsement Test


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Question 1

If you must make an emergency stop, brake so that you:

Can steer and your vehicle will stay in a straight line.
Use the hand brake before the pedal brake.
Use the full power of the brakes to lock them.
Question 1 Explanation: 
Always maintain your ability to steer and if at all possible keep your vehicle straight.
Question 2

You know your brakes are fading when:

The brakes feel spongy when pressure is applied.
You have to press the brake harder when on a downhill grade.
Pressure on the brake pedal is increased and speed increases.
Question 2 Explanation: 
Harder pressure on the brake pedal is needed to maintain speed. At this point brake failure is imminent. Gear down to maintain speed and apply engine retarder (if equipped).
Question 3

If the spring brakes are on, when should you press the brake pedal?

Only on a slippery road.
Only when driving downhill.
Question 3 Explanation: 
Never press the brake pedal when the spring brakes are applied.
Question 4

The use of air brakes on a downgrade is only a supplement to the:

Use of the spring brakes.
Use of the front brake limiting valve.
The braking effect of the engine.
Question 4 Explanation: 
The braking effect of the engine is the primary speed control on a downgrade. Use the brake system sparingly as it may be needed to bring your vehicle to a sudden stop.
Question 5

What is the first thing you should do should a low air warning device come on?

Call a mechanic.
Stop and safely park as soon as possible.
Question 5 Explanation: 
Stop the vehicle! Air is the life blood of the air brake system and it is about to fail should you have a low air warning come on.
Question 6

If the vehicle has an alcohol evaporator, every day during cold weather, you should:

Check the oil level for alcohol
Change the alcohol from a new bottle
Check and fill the alcohol level
Question 7

For air brakes in good condition, the air compressor should start pumping about ______ PSI.

Question 7 Explanation: 
100 PSI is the low point in the air system. The compressor will start pumping and bring the system back up to 125-130 PSI.
Question 8

Which of these is not a proper time to apply your parking brake?

When you park for less than 1 hour
When you're testing to see if they will hold your vehicle
When your brakes are hot
Question 8 Explanation: 
When your brakes are hot. If you apply the parking brake when the brakes are hot, when they cool, they could bind causing brake failure.
Question 9

Repeatedly pressing and releasing the brake pedal (fanning) can result in:

No Change in Brake Pressure
Build-up of Air Pressure
Loss of Air Pressure
Question 9 Explanation: 
Fanning the brake pedal can cause a loss in air pressure. If you lose air pressure, your ability to stop will be hampered or lost.
Question 10

It is not safe to drive a vehicle that has brake drums with cracks that are longer than ____ of the width of the friction area.

Question 10 Explanation: 
Cracks that extend over ½ the friction area can lead to catastrophic failure of the brake drum. If a brake drum fails under pressure it can throw shards of metal towards passing motorist. This must be addressed IMMEDIATELY if found.
Question 11

Excessive use of the service brakes can lead to overheating, which can lead to:

Improper adjustment of S-cam
Expansion of the brake drums
Increased contact between the brake drums and brake lining
Question 11 Explanation: 
Overheating the brakes can lead to expansion of the brake drums which in turn leads to brake fade, brake fade, and eventually brake lining fire.
Question 12

During normal operation, spring brakes are held back by:

Bolts and braces
Air pressure
Question 12 Explanation: 
Air Pressure is used to hold back the spring brakes during normal operation. Should the air pressure fail, then the spring brakes will be automatically actuated.
Question 13

The Air Pressure Governor controls the:

When air is pumped into the storage tanks
The Air pressure applied to the brakes
Speed of the air compressor
Question 13 Explanation: 
The air pressure governor is the controlling valve set that tells the compressor when to add air to the storage tanks.
Question 14

In Air brakes, the parking brake should be used:

As little as possible
Anytime the vehicle is parked
To hold your Speed going downhill
Question 14 Explanation: 
Anytime the vehicle is parked you should use your parking brake
Question 15

What is the slack adjuster?

It is the space between the rear wheels.
It is the adjusting controls on the back side of the drum used for adjusting the brakes.
It is the adjusting controls used to adjust the spring beneath the cab
Question 15 Explanation: 
The slack adjuster adjusts the brakes and is located on the back side of the drum
Question 16

The brake pedal in an air brake system:

Controls the speed of the air compressor
Is connected to the slack adjuster
Controls the amount of air pressure applied to the brakes
Question 17

Air Brake-equipped vehicles have:

A back-up hydraulic system
An Air supply pressure gauge
An Air Use gauge
Question 18

The parking or emergency brake on a heavy vehicle can only be held in position by something that cannot leak away, like:

Spring Pressure
Hydraulic Pressure
Air pressure
Question 19

How should you check that the spring brakes come on when the air pressure in the system drops below a certain level?

Park on a slight incline, drain off air pressure, set the parking brakes, and check for movement.
Park on level ground, wait for normal air pressure, release the parking brake, move the truck forward slowly, and apply the brakes firmly using the brake pedal.
Park on level ground, chock the wheels, release the parking brake when you have enough air pressure, shut the engine off, and repeatedly press and release the brake pedal.
Question 19 Explanation: 
This is considered a brake test. You should perform a brake test during each pretrip. In the event of a failure, report it immediately.
Question 20

The parking brake applies and releases:

The brake pedal during normal driving
The parking brakes when you use the parking brake control
In the event of an emergency
Question 20 Explanation: 
The parking brake applies and releases the SPRING brakes when you use the parking rake control. The “pssssh” sound you hear when a driver sets his brakes is the air escaping that held the spring brakes from applying.
Question 21

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:

Stab braking method
Both the above answers are correct
Controlled Braking method
Question 21 Explanation: 
Both answers are correct. With the advent of anti-lock brake systems the controlled method is preferred.
Question 22

Which of the following does ABS do?

Decreases you normal braking ability
Increases your normal braking ability
Activates when the wheels are about to lock up
Shortens your stopping distance
Question 22 Explanation: 
ABS does not have a huge effect on your everyday driving in that it neither increases nor decreases your braking capability, nor does it necessarily shorten your actual stopping distance. It just helps you keep your vehicle in control, but it activates when your wheels are about to lock up.
Question 23

Why must you study air brakes?

otherwise you will have to get a CDL with restrictions
Otherwise you can only receive a CDL permit
All trucks have air brakes
Question 23 Explanation: 
if you have not studied and passed the section of the CDL exam for air brakes, you can only receive a CDL with a restriction (K) that allows you to drive only vehicles without air brakes. So, good luck!
Question 24

Spring Brakes are:

Come on automatically when the pressure drops too low
Brakes held back by heavy duty springs
Both A & B are correct
Question 24 Explanation: 
Spring brakes are an important "back-up system"--powerful springs that put brakes on if they sense that the air pressure has been lost for some reason, such as with a leak. They will also come on automatically if the psi gets too low, though ideally you should take control of your brakes before the situation reaches this point.
Question 25

How can you tell if your vehicle is equipped with an ABS system?

If the vehicle is manufactured after 1998
If the vehicle is manufactured after 2010
Its still an option on some vehicles
Question 25 Explanation: 
Vehicles made after 1998 are required to have anti-lock brakes. They will also have a yellow ABS malfunction lamp.
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About the Air Brakes CDL Test

The Air Brakes test:

  • 25 questions.
  • You need 20 correct answers (80%).
  • You may be timed. Time limit varies by state. 

Many of the commercial vehicles on the road today use air brakes for their braking system. If you want to pull a trailer with air brakes, you will need to pass the Air Brakes test.

You should also study the Combination Vehicle section of your state’s CDL manual. It is a great idea to study for and pass this exam to broaden your marketability in the trucking industry, as well to be as knowledgeable about other commercial vehicles on the road around you.

The air brakes test is not technically an endorsement. Instead, air brakes are a restriction. If you cannot pass this test, you are restricted from driving vehicles that use air brakes.

Air brakes use compressed air instead of a hydraulic system to stop your vehicle. The air brake system is a three-part system, engaging at different times the service brake, parking brake, and/or emergency brake. The service brake is using the compressed air when you use your foot to depress the brake pedal. The parking brake engages the air supply when you pull on the push/pull knob inside the cab, usually on the dash. Finally, the emergency brake uses a separate air supply to engage parts of both the service and parking brakes to stop the vehicle in an emergency.

There are some images of the different parts of all three braking systems inside the CDL manual. Even for some of you with mechanical backgrounds, studying these images and knowing everything about them will improve your understanding of the brakes, and make you a safer operator.

You will be tested on the following:

  • The parts of an air brake system
  • Dual air brake
  • Inspecting air brake systems
  • Using air brakes

Knowing your braking system is very important—they have a separate test all about one feature of your vehicle! Some sample questions are as follows. Why must air tanks be drained? What are slack adjusters? How should you brake when driving a tractor-trailer combination with ABS?


About The Author
Contributor: Luke Nold (Experienced truck driver for 5+ years and published writer for Fleet Magazine).