TruckingTruth logo

CDL Practice Test: Air Brakes

These CDL practice questions are from our High Road Training Program, a CDL test preparation course designed to help you learn the CDL manual.

Our High Road Training Program has the entire CDL manual built right in along with multiple choice questions, a scoring system, and a review system to help reinforce the materials. It's highly effective, super easy to use, and free! Let me tall ya....using The High Road is a thousand times easier than trying to read the entire CDL manual cover to cover.

Click Here To Learn More

CDL Practice Test: Air Brakes

Air Brakes Questions

Click On The Picture To Begin

Good Luck!

If the air governor stops working properly, which of the following could occur?
  • All of these answers are correct
  • You could encounter steering difficulties
  • The air system may not keep enough air pressure for safe driving
  • You may get increased condensation in your air tanks
This is a question from page 45 - click here to look up the answer

Quote From Page 66 Of The Illinois CDL Manual:

Check air compressor governor cut-in and cut-out pressures:

Pumping by the air compressor should start at about 100 psi and stop at about 125 psi (check manufacturer?s specifications). Run the engine at a fast idle. The air governor should cut out the air compressor at about the manufacturer?s specified pressure. The air pressure shown by your gauge(s) will stop rising. With the engine idling, step on and off the brake to reduce the air tank pressure. The compressor should cut in at about the manufacturer?s specified cut-in pressure. The pressure should begin to rise.

If the air governor does not work as described above, it may need to be repaired. A governor that does not work right may not keep enough air pressure for safe driving.

TruckingTruth's Advice:

It is important to memorize the "cut in" and "cut out" levels for the air governor as well as the terminology.

Cut in: When the governor tells the air compressor to start pumping air into the air tanks. This should occur when air pressure falls to about 100 psi.

Cut out: When the governor tells the air compressor to stop pumping air into the air tanks. This should occur when the air pressure has risen to about 125 psi.

Next
While inspecting the air compressor, you should:
  • Take the front cover off so you can look inside the vacuum seal
  • Check the condition and tightness of the belt (if belt driven)
  • Unbolt the air compressor from the engine as visually inspecting it while attached is nearly impossible
  • Visually check oil level inside the air compressor using a dip-stick
This is a question from page 44 - click here to look up the answer

Quote From Page 66 Of The Illinois CDL Manual:

Check air compressor drive belt if compressor is belt driven. If the air compressor is belt driven, check the condition and tightness of the belt. The belt should be in good condition.

TruckingTruth's Advice:

Some air compressors are gear driven, in which case, no belt will be present. Otherwise, be sure to check the belt to be sure it isn't frayed, cracked, off its tracks, or otherwise broken.

Prev
Next
At what psi will the air compressor governor tell the air compressor to "cut-in"?
  • 110 psi
  • 100 psi
  • 90 psi
  • 120 psi
This is a question from page 45 - click here to look up the answer

Quote From Page 66 Of The Illinois CDL Manual:

Check air compressor governor cut-in and cut-out pressures: Pumping by the air compressor should start at about 100 psi and stop at about 125 psi. (Check manufacturer's specifications.) Run the engine at a fast idle. The air governor should cut out the air compressor at about the manufacturer's specified pressure. The air pressure shown by your gauge(s) will stop rising. With the engine idling, step on and off the brake to reduce the air tank pressure. The compressor should cut in at about the manufacturer's specified cut-in pressure. The pressure should begin to rise.

TruckingTruth's Advice:

It is important to memorize the "cut in" and "cut out" levels for the air governor as well as the terminology.

Cut in: When the governor tells the air compressor to start pumping air into the air tanks. This should occur when air pressure falls to about 100 psi.

Cut out: When the governor tells the air compressor to stop pumping air into the air tanks. This should occur when the air pressure has risen to about 125 psi.

Prev
Next
What is the air brake lag distance at 55 mph on dry pavement?
  • About 47 feet
  • About 25 feet
  • About 38 feet
  • About 32 feet
This is a question from page 46 - click here to look up the answer

Quote From Page 68 Of The Illinois CDL Manual:

The air brake lag distance at 55 mph on dry pavement adds about 32 feet. Therefore, for an average driver traveling 55 mph under good traction and brake conditions, the total stopping distance is more than 300 feet. This is longer than a football field.

TruckingTruth's Advice:

Brake lag is something that all air brake vehicles have. It takes about one-half second for the brakes to start working after you've depressed the brake pedal. This is just one more reason why you should maintain a much larger following distance while driving a commercial vehicle.

Prev
Next
The following are all true about parking brakes, except:
  • When there are freezing temperatures and the brakes are very wet, the brake linings may freeze to the brake drums
  • When the brakes are very hot (i.e. just after coming down a steep grade) wheel chocks should be used instead of the parking brake
  • All of these answers are true
  • Older vehicles may have a round blue knob for the parking brake in place of the yellow diamond shaped knob currently used in modern equipment
This is a question from page 47 - click here to look up the answer

Quote From Page 68 Of The Illinois CDL Manual:

Any time you park, use the parking brakes, except as noted. Pull the parking brake control knob out to apply the parking brakes. Push it in to release them. The control will be a yellow, diamond-shaped knob labeled "parking brakes" on newer vehicles. On older vehicles, it may be a round blue knob or some other shape, including a lever that swings from side to side or up and down.

Do not use the parking brakes if the brakes are very hot (i.e., from just coming down a steep grade), or if the brakes are very wet in freezing temperatures. If the brakes are used when 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 to hold the vehicle. Let hot brakes cool before using the parking brakes. If the brakes are wet, use the brakes lightly while driving in a low gear to heat and dry them.

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.


Never leave your vehicle unattended without applying the parking brakes or chocking the wheels. Your vehicle might roll away and cause injury and damage

Prev
Next
Which of the following is true about Supply Pressure Gauges?
  • If the vehicle has a dual air brake system, there will be a gauge for each half of the system (or a single gauge with two needles)
  • All of these answers are true
  • These gauges tell you how much pressure is in the air tanks
  • All air-brake vehicles have a pressure gauge connected to the air tank
This is a question from page 43 - click here to look up the answer

Quote From Page 64 Of The Illinois CDL Manual:

All air-brake vehicles 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 (or a single gauge with two needles). These gauges tell you how much pressure is in the air tanks.

TruckingTruth's Advice:

Nearly all combination vehicles run on dual air brake systems. Be sure to locate where the gauges are on the dash as well as where the low air pressure warning light is located.

Prev
Next
What is the supply pressure gauge used for?
  • Indicates how much pressure is being supplied to the emergency brake
  • Indicates how much air pressure is in the air holding tanks
  • Indicates how much pressure is being supplied to the service brake
  • Indicates how much pressure is being supplied to the parking brake
This is a question from page 43 - click here to look up the answer

Quote From Page 64 Of The Illinois CDL Manual:

Supply Pressure Gauges - All air-brake vehicles 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 (or a single gauge with two needles). These gauges tell you how much pressure is in the air tank

Prev
Next
Which statement best describes Disc Brakes?
  • The brake chamber push rod pushes a wedge directly between the ends of two brake shoes
  • Air pressure pushes a push rod out, moving the slack adjuster, thus twisting the brake cam shaft
  • When driving, powerful springs are held back by air pressure and if the air pressure is removed, the springs put on the brakes
  • A power screw clamps the disc or rotor between the brake lining pads of a caliper, similar to a large C-clamp
This is a question from page 42 - click here to look up the answer

Quote From Page 64 Of The Illinois CDL Manual:

Disc brakes: In air-operated disc brakes, air pressure acts on a brake chamber and slack adjuster, like S-cam brakes. But instead of the S-cam, a "power screw" is used. The pressure of the brake chamber on the slack adjuster turns the power screw. The power screw clamps the disc or rotor between the brake lining pads of a caliper, similar to a large C-clamp.

TruckingTruth's Advice:

While it is very likely you will only drive a vehicle with S-Cam brakes, you should know the difference between S-Cam brakes, wedge brakes, and disc brakes.

Prev
Finish
Please select an option
[3,2,2,4,3,2,2,4]
8

Ready For A Quiz? Pick A Category:

Join Us!

We have an awesome set of tools that will help you understand the trucking industry and prepare for a great start to your trucking career. Not only that, but everything we offer here at TruckingTruth is 100% free - no strings attached! Sign up now and get instant access to our member's section:
High Road Training Program Logo
  • The High Road Training Program
  • The High Road Article Series
  • The Friendliest Trucker's Forum Ever!
  • Email Updates When New Articles Are Posted

About Us

TruckingTruth was founded by Brett Aquila (that's me!), a 15 year truck driving veteran, in January 2007. After 15 years on the road I wanted to help people understand the trucking industry and everything that came with the career and lifestyle of an over the road trucker. We'll help you make the right choices and prepare for a great start to your trucking career.

Read More

Becoming A Truck Driver

Becoming A Truck Driver is a dream we've all pondered at some point in our lives. We've all wondered if the adventure and challenges of life on the open road would suit us better than the ordinary day to day lives we've always known. At TruckingTruth we'll help you decide if trucking is right for you and help you get your career off to a great start.

Learn More