NE · L (restriction removed) Endorsement

Nebraska Air Brakes CDL Practice Test

Below are 25 exam-style questions for the Nebraska Air Brakes CDL knowledge test, modeled on the FMCSA-aligned content used by the Nebraska Department of Motor Vehicles. Try to answer each question on your own before reading the answer key directly under it. The questions and answer choices are shuffled deterministically per state and endorsement, so the order will stay the same on repeat visits — that lets you genuinely measure your improvement.

Heads up: this is a study tool, not a graded exam. Cover the answer with your hand or a sheet of paper for an honest practice run, then re-read the explanations for any questions you missed. Aim for 22 out of 25 or better, three times in a row, before scheduling the real exam.

Question 1 of 25

After releasing the parking brake on a tractor, you should:

A Drive immediately
B Pump the service brake five times
C Wait for full system pressure before moving
D Drain the wet tank

Correct answer: C

Make sure the system reaches at least the cut-out pressure (typically around 120 psi) before driving.

Question 2 of 25

You should test the trailer service brakes by:

A Pumping them while parked
B Listening for a hiss
C Releasing the parking brakes, moving the vehicle slowly forward, and applying the trailer hand valve
D Looking at the gauge

Correct answer: C

A low-speed pull-and-stop with the trailer hand valve confirms the trailer brakes apply on their own.

Question 3 of 25

A common practice during a long brake-recharge wait is to:

A Allow the system to reach operating pressure before driving
B Check the brake light visibility
C Drain the wet tank
D Disable the warning lamp

Correct answer: A

Always wait for full operating pressure (typically around 120 psi) before moving the vehicle.

Question 4 of 25

Air dryers are used in air-brake systems to:

A Remove moisture and contaminants from the compressed air
B Replace governors
C Cool the air before it enters the brake chambers
D Increase pressure

Correct answer: A

Dryers reduce moisture in the air system, helping prevent corrosion, ice in winter, and contamination.

Question 5 of 25

You should NOT drain the wet tank when:

A There is no situation in which draining is wrong
B It is full of moisture
C You are about to begin a trip
D The vehicle is in motion

Correct answer: A

Daily draining is a routine task; there is no situation where draining is unsafe (other than while driving).

Question 6 of 25

A foot-valve pressure gauge reading lower than expected during a brake application could indicate:

A A new compressor
B Normal operation
C A worn seat belt
D A leak or restriction

Correct answer: D

Low pressure during application means the system isn't delivering full braking force — investigate.

Question 7 of 25

You should test the parking brake by:

A Doing nothing — the dashboard light is enough
B Setting the parking brake, releasing the service brake, and gently trying to move the vehicle
C Driving over a curb
D Pressing the service brake while parked

Correct answer: B

Apply throttle gently in low gear; if the truck moves, the parking brake is not holding.

Question 8 of 25

The total stopping distance for an air-brake equipped vehicle is:

A Reaction + braking + brake-lag distance
B Reaction distance + braking distance
C Perception + braking distance
D Perception + reaction + brake-lag + braking distance

Correct answer: D

Air brakes add a brake-lag distance — the time from foot-pressure to actual brake application — that hydraulic systems do not have.

Question 9 of 25

A brake check ahead of a downgrade should be done:

A At the bottom only
B Once a year
C In the middle of the descent
D Before reaching the top, while still on level ground

Correct answer: D

A brief brake test on level ground at the top reveals problems while you can still stop safely.

Question 10 of 25

During the seven-step air-brake check, the final step is to:

A Pull forward and apply the foot brake to test for stopping
B Adjust the slack adjusters
C Drain the wet tank
D Check tire pressures

Correct answer: A

After all stationary tests, perform a moving brake check at low speed to verify the service brakes stop the vehicle.

Question 11 of 25

On a vehicle with dual air brakes, the warning device must come on before pressure in either system drops below:

A 40 psi
B 60 psi
C Never; only the gauge needs to read it
D 20 psi

Correct answer: B

The low-air warning must activate before pressure drops below 60 psi in either circuit.

Question 12 of 25

Spring brakes do NOT replace:

A The headlights
B The horn
C The service brakes for normal stops
D The tail lights

Correct answer: C

Spring brakes are for parking and emergency only — never for normal service braking.

Question 13 of 25

Which is the proper procedure when the low-air warning comes on while driving?

A Pump the brakes to keep pressure
B Continue to the next exit
C Bring the vehicle to a safe stop as soon as possible and find the cause
D Increase engine RPM

Correct answer: C

Continued driving below safe air pressure risks losing service brakes entirely. Stop safely and diagnose.

Question 14 of 25

When you press the brake pedal, brake pressure is:

A Created by the pedal mechanically
B Released from the storage tanks
C Built up from zero by the pedal
D Received from a separate accumulator

Correct answer: B

Pressing the pedal releases stored air from the tanks into the brake chambers; the pedal does not generate pressure itself.

Question 15 of 25

In a dual system, normal cut-in pressure is approximately:

A 125 psi
B 85 psi
C 40 psi
D 60 psi

Correct answer: D

Cut-in is usually around 100 psi but cut-out is around 125 psi. Cut-in below 60 psi indicates a problem in many systems.

Question 16 of 25

A common cause of an air-brake skid is:

A Both of the above
B Locking the wheels by braking too hard
C Driving too fast for conditions
D Neither of the above

Correct answer: A

Skids result when the wheel locks and the tire loses traction. Speed and over-application are both common contributors.

Question 17 of 25

When applying brakes in an emergency without ABS:

A Press as hard as possible and hold
B Use stab braking — apply hard, release when wheels lock, re-apply
C Pump rapidly and lightly
D Use only the parking brake

Correct answer: B

Stab braking keeps the truck straight in an emergency without ABS. Hard continuous pressure can lock the wheels and cause a jackknife.

Question 18 of 25

Stopping a vehicle with an air-brake failure can sometimes be done by:

A Honking
B Using the trailer hand valve, then engine braking, then a runaway ramp if needed
C Coasting in neutral
D Putting the transmission in reverse

Correct answer: B

In an air-brake failure, the trailer hand valve can still apply the trailer service brakes, then engine braking and a runaway ramp.

Question 19 of 25

When applying brakes in an emergency with ABS:

A Pump rapidly
B Release the brakes immediately
C Press as hard as possible and hold
D Stab the brakes

Correct answer: C

With ABS, full pressure works because the system pulses for you, allowing maximum braking while preserving steering.

Question 20 of 25

Modulating valves on the rear axle help prevent:

A Steering wander
B Wheel lockup during emergency braking
C Tire blowouts
D Engine overheating

Correct answer: B

Modulating valves and ABS sensors release pressure briefly to keep wheels from locking.

Question 21 of 25

Slack adjusters should be checked because:

A They are decorative
B Out-of-adjustment slack adjusters can result in brakes that do not work properly
C They control trailer height
D They affect engine performance

Correct answer: B

Slack adjusters convert pushrod motion into braking force. Out-of-adjustment slack adjusters reduce braking ability and are a common out-of-service item.

Question 22 of 25

The proper braking technique on a long downgrade is:

A Heavy continuous braking
B Apply the parking brake
C Light, intermittent braking with engine braking and a low gear
D Coast in neutral

Correct answer: C

Use the proper low gear so engine braking does most of the work; brief, moderate brake applications keep the speed in check.

Question 23 of 25

Air pressure should normally build from 50 to 90 psi within:

A Less than 30 seconds
B It does not matter
C About 3 minutes in dual systems
D 10 minutes

Correct answer: C

Dual air systems should build from 50 to 90 psi within about 3 minutes at idle.

Question 24 of 25

Glad-hand seals should be:

A Free of dirt and damage and properly seated
B Removed for inspection
C Loose for easy connection
D Coated with oil

Correct answer: A

Damaged or dirty seals cause leaks. Inspect and clean them as part of the trailer hookup.

Question 25 of 25

You should test the service brakes by:

A Pumping the brakes
B Driving at 30 mph and slamming on the brakes
C Listening to the air gauge
D At about 5 mph, applying the brake firmly and feeling for pulling, sticking, or unusual feel

Correct answer: D

A low-speed brake test catches sticking, pulling, or weak brakes before you build up speed.

Study tips for the Nebraska Air Brakes exam

The Air Brakes portion of the Nebraska CDL exam is graded out of the bank of questions the Nebraska Department of Motor Vehicles draws from each year. While the exact bank is not published, every question is sourced from the Air Brakes chapter of the Nebraska CDL handbook, which itself is derived from the FMCSA Model Commercial Driver's License Manual. That means studying our practice tests, reading the corresponding handbook chapter, and re-reading the parts you got wrong is genuinely the most efficient route to a first-time pass.

Most successful applicants follow a simple cycle: take the practice test cold, write down every question you missed, open the matching chapter of the official Nebraska handbook, re-read the section that contains the right answer, then re-take the practice test 24 to 48 hours later. The 24-hour delay matters — sleep is when your brain commits new information to long-term memory, and CDL knowledge questions reward that kind of consolidated learning rather than cramming.

Pay particular attention to questions that include qualifier words like always, never, only, primary, or most. CDL test writers love to flip the right answer with a single qualifier. When two answer choices look almost identical, pay attention to the verb (is it must, should, or may?) and to any numbers (14 days, 100 air miles, 8 hours, 70/8 split). On endorsement tests in particular, watch for trick framing where a true statement about a different endorsement is offered as the "correct" answer to a question that is actually about Air Brakes.

Test-day logistics matter too. Bring photo ID, your Social Security card or birth certificate, your medical examiner's certificate (DOT card), and proof of state residency if you haven't already submitted those documents. The Nebraska Department of Motor Vehicles will not let you sit for the knowledge exam without your documentation, and most offices charge an additional fee for re-attempts. Arrive early — the wait at most CDL testing offices runs 30 to 60 minutes — and silence your phone before the exam begins.

Finally, keep your General Knowledge fundamentals sharp even when you're focused on the Air Brakes exam. Many states administer multiple knowledge tests in a single sitting, and questions on weight definitions (GVWR, GCWR, GAWR), stopping distance, and the pre-trip inspection routine show up across endorsements. If you're unsure on the basics, sit a fresh Nebraska General Knowledge practice test before scheduling the real exam.

Next steps

Missed more than four questions? Re-read the Air Brakes study guide and the matching chapter in the official Nebraska CDL handbook. Then come back and re-take the test. Once you can score 22 of 25 or higher on three runs in a row, you're in good shape to schedule the real exam at your local Nebraska Department of Motor Vehicles office.

Already comfortable with this endorsement? Drill another: NE General Knowledge · NE Combination Vehicles · NE Hazardous Materials · NE Passenger · NE School Bus · NE Tank Vehicle · NE Doubles / Triples

New to the CDL process in Nebraska? Read How to apply for a CDL in Nebraska for the document checklist and step-by-step timeline.