Free Pennsylvania DMV CDL — Air Brakes Practice Test 2026
The Pennsylvania CDL — Air Brakes knowledge test has ~25 questions, and you need ~20 correct (80%) to pass. Practice free with questions written from the official Pennsylvania driver handbook — every one has a clear explanation, and you can retake as often as you like with no sign-up.
Content reviewed against official driver handbooks · August 12, 2026
What's on the Pennsylvania written test
The Pennsylvania CDL — Air Brakes knowledge test has ~25 questions; you need ~20 correct (80%) to pass.
Based on the official Pennsylvania exam format — always confirm current details with your state DMV.
Practice by topic
Focus on one area at a time — each topic has its own set of Pennsylvania practice questions.
How to pass the first time
- Read the official Pennsylvania driver handbook at least once before test day.
- Practice by topic to find your weak spots, then fix them.
- Take full-length practice tests until you pass comfortably every time.
- Read every explanation — understanding beats memorizing.
Pennsylvania CDL — Air Brakes test — frequently asked questions
How many questions are on the Pennsylvania CDL — Air Brakes test?
The Pennsylvania CDL — Air Brakes knowledge test has ~25 questions, and you need ~20 correct (80%) to pass. Our practice tests mirror that format.
How many questions can I miss on the Pennsylvania CDL — Air Brakes test?
You can miss up to ~5 of the ~25 questions and still pass — you need ~20 correct, which is 80%.
Can I retake the practice test?
Yes — practice as often as you like, completely free. The questions and answer choices are shuffled each time.
Can I take the Pennsylvania practice test in Spanish?
Yes. Every question here is available in English and Spanish — switch languages anytime. Many states also offer the real knowledge test in languages other than English; confirm what Pennsylvania offers with your DMV.
Can I practice on my phone?
Yes. The practice tests work in any mobile or desktop browser — no app or sign-up needed — so you can study anywhere.
Are these the real DMV test questions?
No. Our questions are original, written from the current official Pennsylvania driver handbook to match the real test's topics and style. We are not affiliated with any DMV or government agency.
What's the best way to study?
Read the Pennsylvania driver handbook, practice by topic to target weak areas, and finish with full-length tests until you consistently pass.
Other Pennsylvania practice tests
Take the CDL — Air Brakes test in another state
Every Pennsylvania question is written from the official Pennsylvania driver handbook and checked against its current edition. DMV Test Free is a free, independent study resource — not affiliated with any DMV or government agency. About DMV Test Free
Pennsylvania CDL — Air Brakes questions with answers
20 sample questions from the Pennsylvania CDL — Air Brakes question bank — each with the correct answer, a short explanation, and the section of the official handbook it comes from.
Show all 20 questions with answers
1. How is the air compressor typically driven?
Correct answer: Through gears or a v-belt tied to the engine
The compressor gets its drive from the engine, using either gears or a v-belt.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.1.1 - Air Compressor
2. What causes brake fade?
Correct answer: Too much heat from overuse, which reduces lining friction and expands the drums
Fade comes from too much heat: overuse changes the lining chemically and cuts its friction, and it expands the drums.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.4.5 - Brake Fading or Failure
3. A visible low-air-pressure warning must come on before tank pressure drops below what level?
Correct answer: 55 psi
Air brake vehicles must have a visible low-air warning that alerts you before tank pressure falls under 55 psi.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.1.11 - Low Air Pressure Warning
4. On newer air brake vehicles, how do you apply the parking (spring) brakes?
Correct answer: Pull out the yellow, diamond-shaped control knob
On newer vehicles you pull out the yellow, diamond-shaped push-pull knob to set the parking (spring) brakes.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.1.15 - Parking Brake Controls
5. How are the powerful springs in spring brakes kept from applying while you drive?
Correct answer: Air pressure holds them back, and losing that air lets them apply
Air pressure holds the springs back as you drive; if that air is lost, the springs set the brakes.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.1.14 - Spring Brakes
6. In an s-cam brake, what happens when you press the brake pedal?
Correct answer: Air enters the chamber, and the rod turns the s-cam so the shoes press against the drum
Air fills the chamber, and the push rod moves the slack adjuster and rotates the s-cam, which forces the shoes against the drum.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.1.8 - Foundation Brakes
7. When using proper (snub) braking on a long downgrade, the brakes serve as what?
Correct answer: A supplement to engine braking, after you are in the proper low gear
On a long grade the brakes only back up the engine's braking, and you select a low gear first.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.4.6 - Proper Braking Technique
8. Truck tractors with air brakes are required to have ABS if built on or after what date?
Correct answer: March 1, 1997
Air-braked truck tractors built on or after March 1, 1997 are required to have antilock brakes.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.1.16 - Antilock Braking Systems (ABS)
9. When should you skip setting the parking brakes and use wheel chocks instead?
Correct answer: When the brakes are very hot, or very wet in freezing weather
Leave the parking brakes off and chock the wheels when the brakes are very hot or are very wet in freezing weather.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.4.8 - Parking Brakes
10. Why is it a bad idea to repeatedly press and release the brake pedal when it isn't necessary?
Correct answer: It can let air out quicker than the compressor restores it, risking loss of braking
Needlessly working the pedal bleeds air out faster than the compressor can rebuild it, and if pressure gets too low you lose braking.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.1.7 - The Brake Pedal
11. The most common kind of foundation brake on heavy vehicles is which type?
Correct answer: The s-cam drum brake
The s-cam drum brake is the most common foundation brake; wedge and disc brakes are less common.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.1.8 - Foundation Brakes
12. Total stopping distance for an air brake vehicle is made up of which four parts?
Correct answer: The perception and reaction distances, plus the brake-lag and braking distances
Total stopping distance combines the perception, reaction, brake-lag and braking distances.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.4.4 - Stopping Distance
13. How does an air brake system light up the brake lights for the drivers behind you?
Correct answer: An air-pressure-operated electric switch turns them on as you brake
An electric switch that is worked by air pressure turns the brake lights on when you apply the brakes.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.1.12 - Stop Light Switch
14. Why should you avoid pressing the brake pedal while the spring brakes are set?
Correct answer: The combined force of the springs and the air pressure could damage the brakes
Pressing the pedal with the spring brakes set can harm the brakes, because the spring force and the air pressure combine.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.1.15 - Parking Brake Controls
15. Which sequence correctly describes stab braking?
Correct answer: Brake hard, release when the wheels lock, then reapply fully as they begin rolling
Stab braking is braking hard, releasing the moment the wheels lock, then fully reapplying once the wheels start rolling again.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.4.3 - Emergency Stops
16. The brake pedal on an air brake vehicle is also known by which other names?
Correct answer: The foot valve or treadle valve
The brake pedal is also called the foot valve or the treadle valve.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.1.7 - The Brake Pedal
17. At 55 mph in good conditions, the total stopping distance for an air brake vehicle is greater than about how many feet?
Correct answer: More than 300 feet
At 55 mph in good conditions, the total stopping distance works out to more than 300 feet.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.4.4 - Stopping Distance
18. Other air brake vehicles such as trucks, buses, trailers and converter dollies must have ABS if built on or after which date?
Correct answer: March 1, 1998
Other air-braked vehicles, including trucks, buses, trailers and dollies, must have ABS if built on or after March 1, 1998.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.1.16 - Antilock Braking Systems (ABS)
19. After you release the brakes during stab braking, about how long can it take for the wheels to start rolling again?
Correct answer: As much as one second
After releasing, it can take as much as a second for the wheels to begin rolling again.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.4.3 - Emergency Stops
20. What is the job of the air compressor governor?
Correct answer: It regulates the points at which the compressor starts and stops adding air to the tanks
The governor decides when the compressor loads air into the tanks and when it stops, keeping tank pressure within its normal band.
Source: Pennsylvania Commercial Driver's Manual (PUB 223), Section 5.1.2 - Air Compressor Governor