MT · L (restriction removed) Endorsement

Montana Air Brakes CDL Practice Test

Below are 25 exam-style questions for the Montana Air Brakes CDL knowledge test, modeled on the FMCSA-aligned content used by the Montana Motor Vehicle Division. 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

Front-wheel brakes are required on commercial vehicles because:

A They reduce stopping distance significantly without normally causing skids on dry pavement
B They make steering easier
C Federal law mandates them as decorative
D They look balanced

Correct answer: A

Front brakes provide a large share of stopping force and modern vehicles are designed so they do not cause front-wheel skids on dry pavement.

Question 2 of 25

After making the initial brake application, the air-pressure drop should not exceed:

A 1 psi
B 10 psi
C 2-3 psi
D 5 psi

Correct answer: C

A small initial drop is normal as the system equalizes — but excessive drop indicates a leak.

Question 3 of 25

When the air pressure in the brake system drops too low:

A Spring brakes apply automatically
B Nothing happens until you stop
C The trailer hand valve releases
D The engine stops

Correct answer: A

When system pressure drops, typically below 20-45 psi, mechanical springs apply the brakes regardless of driver input.

Question 4 of 25

A common cause of an air-brake skid is:

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

Correct answer: B

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

Question 5 of 25

Modulating valves on the rear axle help prevent:

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

Correct answer: A

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

Question 6 of 25

You should NOT drain the wet tank when:

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

Correct answer: D

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

Question 7 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 Disable the warning lamp
D Drain the wet tank

Correct answer: A

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

Question 8 of 25

The air-brake hand valve (trolley valve) operates:

A The parking brake
B The tractor service brakes only
C The trailer service brakes only
D Both tractor and trailer brakes

Correct answer: C

The hand valve applies only the trailer service brakes. It is not a parking brake or a substitute for the foot brake.

Question 9 of 25

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

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

Correct answer: A

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

Question 10 of 25

You should test the trailer service brakes by:

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

Correct answer: A

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

Question 11 of 25

When applying brakes in an emergency without ABS:

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

Correct answer: C

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

Question 12 of 25

Each axle group on an air-brake-equipped vehicle has its own:

A Drive shaft
B Air compressor
C Engine
D Set of brake chambers

Correct answer: D

Each axle group has its own brake chambers fed by the air system; one compressor supplies all of them.

Question 13 of 25

Why should you NOT use the trailer hand valve to hold a parked combination vehicle?

A Air leaks could cause the brakes to release and let the vehicle roll
B It is illegal
C It will activate the spring brakes
D It only works while the engine is running

Correct answer: A

The hand valve relies on continuous air pressure. A slow leak releases the brakes and the vehicle rolls.

Question 14 of 25

Anti-lock braking systems (ABS) on air-brake vehicles:

A Are optional and rarely installed
B Help prevent wheel lockup but do not necessarily shorten stopping distance
C Replace foundation brakes
D Are required only on hazmat trailers

Correct answer: B

ABS helps the driver maintain steering control by preventing wheel lockup. It does not necessarily reduce stopping distance.

Question 15 of 25

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

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

Correct answer: D

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

Question 16 of 25

In a combination vehicle, with the brakes applied and the engine off, the maximum allowable air loss is:

A 5 psi per minute
B 4 psi per minute
C 3 psi per minute
D 2 psi per minute

Correct answer: B

Combination vehicle, brakes applied: 4 psi per minute. Single vehicle, brakes applied: 3 psi per minute.

Question 17 of 25

Glad-hand seals should be:

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

Correct answer: B

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

Question 18 of 25

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

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

Correct answer: A

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 19 of 25

Slack adjusters should be checked because:

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

Correct answer: D

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 20 of 25

When you press the brake pedal, brake pressure is:

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

Correct answer: C

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

Question 21 of 25

Air dryers are used in air-brake systems to:

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

Correct answer: A

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

Question 22 of 25

You should not over-tighten a glad-hand because:

A It can damage the rubber seals
B It violates federal weight law
C It is bad luck
D It will reduce engine power

Correct answer: A

Over-tightening crushes the seals. The connection should be firm but not forced.

Question 23 of 25

Cross-leakage between primary and secondary brake systems is:

A A serious defect that can prevent backup braking
B Required by federal law
C Caused by overuse
D A normal feature

Correct answer: A

Each circuit must remain independent so a failure in one still leaves the other working.

Question 24 of 25

Which is true about air storage tanks?

A They drain themselves automatically in all trucks
B They never need to be drained
C They must be drained completely once a year
D They must be drained daily to remove water and oil

Correct answer: D

Most trucks require manual daily draining of each tank. Some have automatic moisture ejectors, but the driver is still responsible.

Question 25 of 25

Spring-brake pop-out occurs at approximately:

A 20 to 45 psi
B 90 to 100 psi
C 60 to 80 psi
D 0 to 10 psi

Correct answer: A

Pop-out is typically between 20 and 45 psi, varying by manufacturer.

Study tips for the Montana Air Brakes exam

The Air Brakes portion of the Montana CDL exam is graded out of the bank of questions the Montana Motor Vehicle Division draws from each year. While the exact bank is not published, every question is sourced from the Air Brakes chapter of the Montana 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 Montana 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 Montana Motor Vehicle Division 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 Montana 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 Montana 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 Montana Motor Vehicle Division office.

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

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