AL · L (restriction removed) Endorsement

Alabama Air Brakes CDL Practice Test

Below are 25 exam-style questions for the Alabama Air Brakes CDL knowledge test, modeled on the FMCSA-aligned content used by the Alabama Law Enforcement Agency (ALEA) Driver License 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

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 2 of 25

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

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

Correct answer: A

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

Question 3 of 25

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

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

Correct answer: C

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

Question 4 of 25

A driver should never:

A Use the trailer hand valve as a parking brake
B Test the parking brake
C Drain the wet tank
D Make pre-trip inspections

Correct answer: A

The trailer hand valve is not a parking device — see the trailer-hand-valve question. Always set the trailer parking brakes.

Question 5 of 25

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

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

Correct answer: D

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

Question 6 of 25

If air pressure drops in the emergency line:

A Trailer service brakes apply
B Nothing happens
C Tractor brakes apply
D Trailer spring brakes apply automatically

Correct answer: D

Loss of supply-line pressure is the failsafe that triggers the trailer's spring brakes.

Question 7 of 25

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

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

Correct answer: A

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

Question 8 of 25

When you press the brake pedal, brake pressure is:

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

Correct answer: A

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

Question 9 of 25

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

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

Correct answer: C

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

Question 10 of 25

A common reason for compressor failure to keep up is:

A All of the above
B A broken governor
C A clogged air filter or worn compressor
D A leak in the brake system

Correct answer: A

Any of these causes can prevent the compressor from maintaining cut-out pressure.

Question 11 of 25

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

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

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 12 of 25

Brake drums in good condition will:

A Be glowing red after stops
B Have small cracks
C Be coated with oil
D Be free of cracks longer than half the width of the friction area

Correct answer: D

Cracks longer than half the friction area or any visible heat checks usually fail inspection.

Question 13 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 Listening for a hiss
C Pumping them while parked
D Looking at the gauge

Correct answer: A

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

Question 14 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 15 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 16 of 25

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

A Have no indication
B Stay pushed in
C Flash red
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

After parking a tractor-trailer:

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

Correct answer: D

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

Question 18 of 25

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

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

Correct answer: A

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

Question 19 of 25

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

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

Correct answer: D

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

Question 20 of 25

When approaching a long downgrade, you should:

A Skip the brake test
B Coast in neutral
C Test the brakes at the bottom
D Test the brakes by lightly applying them at the top

Correct answer: D

A light brake application at the top tests for pulling or weakness before the descent puts heat into the system.

Question 21 of 25

You should test the service brakes by:

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

Correct answer: C

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

Question 22 of 25

When applying brakes in an emergency with ABS:

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

Correct answer: A

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

Question 23 of 25

A dual air-brake system means:

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

Correct answer: A

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 24 of 25

A brake check ahead of a downgrade should be done:

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

Correct answer: C

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

Question 25 of 25

Spring brakes are held off by:

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

Correct answer: D

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

Study tips for the Alabama Air Brakes exam

The Air Brakes portion of the Alabama CDL exam is graded out of the bank of questions the Alabama Law Enforcement Agency (ALEA) Driver License Division draws from each year. While the exact bank is not published, every question is sourced from the Air Brakes chapter of the Alabama 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 Alabama 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 Alabama Law Enforcement Agency (ALEA) Driver License 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 Alabama 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 Alabama 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 Alabama Law Enforcement Agency (ALEA) Driver License Division office.

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

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