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200+ Free Alabama CDL Air Brakes Practice Questions

Pass your Alabama CDL Air Brakes Knowledge Test exam on the first try — instant access, no signup required.

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For an Alabama CDL air-brake vehicle, in normal stops with air brakes, you should:

A
B
C
D
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2026 Statistics

Key Facts: Alabama CDL Air Brakes Exam

80%

Minimum CDL knowledge-test passing score

49 CFR 383.135

7

Required federal air-brake knowledge areas

49 CFR 383.111(b)

$25

ALEA CDL testing fee

ALEA Document Requirements and Fees

360 days

Alabama CLP validity

ALEA CDL FAQ

14 days

Minimum CLP hold before CDL skills testing for first-time/upgrading applicants

ALEA CDL FAQ

55 psi

Low-air warning must activate before pressure drops below this value in Alabama manual

Alabama CDL Manual Section 5

20-45 psi

Typical manufacturer range for spring brake pop-out/application

Alabama CDL Manual Section 5

85 to 100 psi

Dual-system buildup range that should be reached within 45 seconds at operating rpm

Alabama CDL Manual Section 5

Use ALEA CDL Manual Section 5 as the primary source for the Alabama CDL Air Brakes test. FMCSA requires the separate air-brake knowledge test to cover seven areas in 49 CFR 383.111(b), and 49 CFR 383.135 requires at least 80% correct. ALEA lists a $25 CDL testing fee, a 360-day nonrenewable CLP, and a 14-day CLP holding period before CDL skills testing for first-time or upgrading applicants. Key numbers include about 100 psi governor cut-in, about 125 psi cut-out, 150 psi safety valve, low-air warning before 55 psi, spring brakes at 20-45 psi, 85-to-100 psi buildup within 45 seconds in dual systems, and leak-rate limits of 2/3 psi released and 3/4 psi applied for single/combination vehicles.

Sample Alabama CDL Air Brakes Practice Questions

Try these sample questions to test your Alabama CDL Air Brakes exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 200+ question experience with AI tutoring.

1For Alabama CDL air-brake testing, what component compresses air for the air brake system?
A.The air dryer
B.The air compressor
C.The brake chamber
D.The slack adjuster
Explanation: The air compressor pumps air into the air storage tanks. It is driven by the engine, either through belts or directly. The air dryer removes moisture from the compressed air, the brake chamber converts air pressure into mechanical force at each wheel, and the slack adjuster transfers that force to the S-cam. This Alabama version is aligned to ALEA CDL Manual Section 5 and FMCSA CDL air-brake standards.
2Under ALEA CDL Manual Section 5, what is the typical air compressor governor cut-out pressure range?
A.60 to 80 psi
B.100 to 125 psi
C.125 to 140 psi
D.150 to 175 psi
Explanation: The governor cuts out the compressor (stops pumping) at about 125 to 140 psi. It cuts back in (resumes pumping) at about 100 to 125 psi. This pressure range keeps the system safely above the low-pressure warning threshold of 60 psi while preventing over-pressurization. This Alabama version is aligned to ALEA CDL Manual Section 5 and FMCSA CDL air-brake standards.
3On the Alabama CDL Air Brakes test, at what pressure does the air compressor governor typically cut IN to resume pumping?
A.60 to 80 psi
B.100 to 125 psi
C.125 to 140 psi
D.145 to 150 psi
Explanation: The governor typically cuts in at 100 to 125 psi, signaling the compressor to resume pumping. It cuts out at 125 to 140 psi when system pressure is sufficient. Together these limits maintain a safe operating range well above the 60 psi low-pressure warning. This Alabama version is aligned to ALEA CDL Manual Section 5 and FMCSA CDL air-brake standards.
4For an Alabama CDL air-brake vehicle, what is the purpose of the air dryer in the brake system?
A.To cool the air before storage
B.To remove moisture and oil before air reaches the tanks
C.To increase compressed air pressure
D.To warn the driver of low pressure
Explanation: The air dryer uses a desiccant cartridge to remove water vapor and oil from compressed air before it enters the storage tanks. Removing moisture prevents corrosion, contamination of brake components, and dangerous freezing of air lines in cold weather. This Alabama version is aligned to ALEA CDL Manual Section 5 and FMCSA CDL air-brake standards.
5For Alabama CDL air-brake testing, what is the function of the wet tank (supply or service reservoir)?
A.It cools brake fluid
B.It is the first storage tank where moisture collects before air moves to the other tanks
C.It supplies air only to the trailer
D.It activates the parking brakes
Explanation: The wet tank is the first storage reservoir downstream of the compressor. Most moisture and oil that gets past the air dryer settles there before clean air moves on to the primary and secondary tanks. Drivers must drain the wet tank daily to prevent contamination of the rest of the system. This Alabama version is aligned to ALEA CDL Manual Section 5 and FMCSA CDL air-brake standards.
6Under ALEA CDL Manual Section 5, at what pressure does the safety valve in the supply tank typically open to release excess air?
A.100 psi
B.125 psi
C.150 psi
D.200 psi
Explanation: The safety valve, installed in the supply (wet) tank, is set to open at about 150 psi. It is a backup that protects the system if the governor fails to cut out the compressor. If the valve releases, the compressor or governor needs immediate repair. This Alabama version is aligned to ALEA CDL Manual Section 5 and FMCSA CDL air-brake standards.
7On the Alabama CDL Air Brakes test, what is the role of the foot valve (also called the treadle or service brake valve)?
A.It locks the parking brake
B.It supplies air to the brake chambers in proportion to how hard the driver presses the pedal
C.It drains water from the tanks
D.It controls the trailer air supply
Explanation: The foot valve (treadle valve) meters air to the brake chambers in proportion to how far the driver depresses the brake pedal. Pressing harder sends more air, applying more braking force. Releasing the pedal exhausts air from the chambers, allowing the springs and slack adjusters to release the brakes. This Alabama version is aligned to ALEA CDL Manual Section 5 and FMCSA CDL air-brake standards.
8For an Alabama CDL air-brake vehicle, what does the brake chamber do?
A.Stores compressed air for emergencies
B.Converts air pressure into mechanical force through a pushrod
C.Cools brake drums during use
D.Acts as a backup for the parking brake
Explanation: A brake chamber is a sealed housing with a diaphragm or piston. When air pressure enters, the diaphragm pushes a pushrod outward. The pushrod rotates the slack adjuster and S-cam, which forces the brake shoes against the drum to apply braking force. This Alabama version is aligned to ALEA CDL Manual Section 5 and FMCSA CDL air-brake standards.
9For Alabama CDL air-brake testing, what is the role of the slack adjuster on an S-cam brake?
A.It cushions the impact of hard braking
B.It transfers force from the pushrod to the S-cam and can be adjusted to compensate for lining wear
C.It bleeds water from the system
D.It limits maximum air pressure
Explanation: The slack adjuster is a lever that connects the brake chamber pushrod to the S-cam. As the pushrod extends, the slack adjuster rotates the S-cam, which pushes the brake shoes against the drum. It can be adjusted to maintain proper pushrod travel as brake linings wear. This Alabama version is aligned to ALEA CDL Manual Section 5 and FMCSA CDL air-brake standards.
10Under ALEA CDL Manual Section 5, what does the S-cam do in an S-cam drum brake?
A.It releases air from the lines
B.It rotates between the brake shoes, forcing them outward against the drum
C.It cools the brake drum
D.It activates the low-pressure warning
Explanation: The S-cam is an S-shaped piece of steel between the two brake shoes. When the slack adjuster rotates it, the wide part of the S forces the shoes outward against the drum, creating friction and slowing the wheel. When air pressure is released, return springs pull the shoes back and rotate the S-cam to its original position. This Alabama version is aligned to ALEA CDL Manual Section 5 and FMCSA CDL air-brake standards.

About the Alabama CDL Air Brakes Exam

The Alabama CDL Air Brakes Knowledge Test is required for Alabama CDL or CLP applicants who need to operate commercial motor vehicles equipped with air brakes or air-over-hydraulic brakes without an air-brake restriction. The test is drawn from the Alabama Commercial Driver License Manual, especially Section 5, and must satisfy FMCSA CDL knowledge-test standards in 49 CFR Part 383. Study areas include air compressor and governor operation, air tanks and drains, contaminated air, low-air warning devices, dual air systems, spring and parking brakes, ABS, brake lag and stopping distance, emergency braking, brake fade, downgrade braking, foundation brakes, slack adjusters, air-leak and buildup tests, and the legacy front brake limiting valve.

Assessment

Separate multiple-choice CDL air-brake knowledge test based on Alabama CDL Manual Section 5 and the seven FMCSA air-brake knowledge areas in 49 CFR 383.111(b).

Time Limit

No separate public time limit published by ALEA

Passing Score

At least 80% correct under 49 CFR 383.135

Exam Fee

$25 CDL testing fee; CLP/CDL issuance and skills-test fees are separate (Alabama Law Enforcement Agency (ALEA))

Alabama CDL Air Brakes Exam Content Outline

25%

Air Brake System Parts

Compressor, governor, storage tanks, drains, alcohol evaporator, safety valve, brake pedal, foundation brakes, gauges, stop light switch, ABS, and front brake limiting valve.

15%

Dual Air Systems and Warnings

Primary and secondary systems, pressure gauges, minimum operating pressure, low-air warning devices, wig-wag operation, and low-pressure response.

30%

Inspection and Air Tests

Compressor belt, slack adjuster travel, automatic slack adjuster cautions, drums and linings, hoses, governor checks, leak tests, warning test, spring-brake pop-out, buildup, parking brake, and service brake checks.

20%

Using Air Brakes

Normal stops, controlled and stab braking, ABS use, brake lag, stopping distance, brake fade, downhill braking technique, low-air emergencies, and parking brake exceptions.

10%

Alabama and FMCSA Rules

ALEA CDL testing logistics, CLP validity and holding period, L and Z air-brake restrictions, 49 CFR Part 383 required knowledge, and the 80% passing standard.

How to Pass the Alabama CDL Air Brakes Exam

What You Need to Know

  • Passing score: At least 80% correct under 49 CFR 383.135
  • Assessment: Separate multiple-choice CDL air-brake knowledge test based on Alabama CDL Manual Section 5 and the seven FMCSA air-brake knowledge areas in 49 CFR 383.111(b).
  • Time limit: No separate public time limit published by ALEA
  • Exam fee: $25 CDL testing fee; CLP/CDL issuance and skills-test fees are separate

Keys to Passing

  • Complete 500+ practice questions
  • Score 80%+ consistently before scheduling
  • Focus on highest-weighted sections
  • Use our AI tutor for tough concepts

Alabama CDL Air Brakes Study Tips from Top Performers

1Memorize the pressure numbers first: about 100 psi cut-in, about 125 psi cut-out, 150 psi safety valve, warning before 55 psi, spring brakes at 20-45 psi, and 85-to-100 psi buildup within 45 seconds in dual systems.
2Practice the final air-brake check as a sequence: governor, leak rates, low-pressure warning, spring-brake pop-out, buildup, parking brake, and service brake.
3Separate service, parking, and emergency brake functions; many missed questions confuse foot-valve braking with spring parking brakes.
4Do not skip legacy topics. Alabama Section 5 still tests front brake limiting valves and wig-wag warnings even though they are older equipment.
5Review ABS carefully: it helps prevent wheel lockup and maintain control, but it does not necessarily shorten stopping distance or increase normal braking power.
6Use only official ALEA, FMCSA, and CFR sources for final review; competitor practice-test wording can conflict with the manual.

Frequently Asked Questions

Who administers the Alabama CDL Air Brakes Knowledge Test?

The Alabama Law Enforcement Agency (ALEA) administers Alabama CDL knowledge testing through its Driver License Division and CDL offices. The official study source is the Alabama Commercial Driver License Manual published by ALEA.

What should I study for the Alabama CDL Air Brakes test?

Study Alabama CDL Manual Section 5. It covers air brake system parts, dual air brake systems, inspection checks, air-leak and buildup tests, low-air warnings, spring brakes, ABS, brake lag, emergency braking, brake fade, downgrade braking, parking brakes, and legacy front brake limiting valves.

What score do I need to pass?

Federal CDL standards in 49 CFR 383.135 require at least 80% correct on each CDL knowledge test, including the air-brake portion.

How much does CDL testing cost in Alabama?

ALEA lists a $25 testing fee for CDL or CDL learner license applicants. CLP/CDL issuance fees, skills-test fees, medical costs, TSA fees, and training costs are separate when they apply.

What happens if I do not pass or do not take the air-brake knowledge component?

Under 49 CFR Part 383 and the Alabama CDL Manual, a CLP or CDL issued after failing or not taking the air-brake component must show an air-brake restriction. That restriction limits operation of CMVs equipped with air brakes.

Is air brakes an endorsement?

Air brakes are commonly discussed like a separate CDL knowledge test, but federally the issue is an air-brake restriction rather than an endorsement. Passing the knowledge component and demonstrating air-brake inspection/operation as required helps avoid or remove that restriction.