IN · L (restriction removed) Endorsement

Indiana Air Brakes CDL Practice Test

Below are 25 exam-style questions for the Indiana Air Brakes CDL knowledge test, modeled on the FMCSA-aligned content used by the Indiana Bureau 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

Front-wheel brakes are required on commercial vehicles because:

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

Correct answer: B

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

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

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

Correct answer: C

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

Question 3 of 25

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

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

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 4 of 25

Which is true about air storage tanks?

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

Correct answer: C

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

Question 5 of 25

A dual air-brake system means:

A Two governors
B Two compressors
C Twice the air pressure
D Two separate air-brake systems on one set of brake controls

Correct answer: D

Modern trucks have two separate air systems (often labeled primary and secondary) with one set of brake controls so a failure in one circuit still leaves working brakes.

Question 6 of 25

After parking a tractor-trailer:

A Set only the trailer parking brake
B Set only the tractor parking brake
C Set both tractor and trailer parking brakes
D Leave both released

Correct answer: C

Federal practice is to set both parking brakes when fully parked. The exception is during coupling/uncoupling, where the trailer brakes are set.

Question 7 of 25

A brake check ahead of a downgrade should be done:

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

Correct answer: A

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

Question 8 of 25

Spring-brake pop-out occurs at approximately:

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

Correct answer: A

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

Question 9 of 25

Slack adjusters should be checked because:

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

Correct answer: A

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 10 of 25

If the ABS warning light comes on while driving, you should:

A Disconnect the trailer
B Continue driving — you still have normal brakes — and have the system checked at the next opportunity
C Pump the brakes hard
D Immediately stop on the side of the road

Correct answer: B

A failed ABS system reverts to normal braking. Get it repaired but you can complete the trip.

Question 11 of 25

You should test the parking brake by:

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

Correct answer: C

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

Question 12 of 25

Modulating valves on the rear axle help prevent:

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

Correct answer: A

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

Question 13 of 25

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

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

Correct answer: B

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

Question 14 of 25

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

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

Correct answer: D

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 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 16 of 25

When the parking brake is set, the dashboard valve will normally:

A Flash red
B Stay pushed in
C Have no indication
D Stay popped out and yellow

Correct answer: D

Yellow diamond-shaped valves stay out (popped) when parking brakes are applied; pushing them in releases the brakes.

Question 17 of 25

When testing low-air warning, you should:

A Pump the brake to fan down the pressure and verify the warning activates before pressure drops below 60 psi
B Disconnect the trailer
C Drain the wet tank only
D Look at the dashboard light

Correct answer: A

Fan the brakes (engine off) until the warning device activates and confirm it is above 60 psi.

Question 18 of 25

When applying the foot brake hard:

A The compressor cuts out
B Air pressure may drop slightly
C Air pressure increases
D Air pressure should remain unchanged

Correct answer: B

A small drop is expected during heavy application. The compressor recharges the system back up to cut-out pressure.

Question 19 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 20 of 25

Air pressure builds back up by:

A The vehicle's motion
B The compressor pumping air back into the storage tanks
C The driver inflating the tank with a portable pump
D The brake pedal

Correct answer: B

The engine-driven compressor refills the tanks; the brake pedal only controls release of stored air.

Question 21 of 25

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

A 85 psi
B 125 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 22 of 25

Spring brakes are held off by:

A Air pressure
B Electrical current
C Engine vacuum
D Hydraulic pressure

Correct answer: A

Compressed air holds the springs back. When air pressure drops, the springs apply the brakes mechanically.

Question 23 of 25

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

A Engine
B Drive shaft
C Air compressor
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 24 of 25

The proper braking technique on a long downgrade is:

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

Correct answer: D

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

Question 25 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 Never; only the gauge needs to read it
C 20 psi
D 60 psi

Correct answer: D

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

Study tips for the Indiana Air Brakes exam

The Air Brakes portion of the Indiana CDL exam is graded out of the bank of questions the Indiana Bureau 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 Indiana 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 Indiana 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 Indiana Bureau 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 Indiana 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 Indiana 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 Indiana Bureau of Motor Vehicles office.

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

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