Free Delaware DMV CDL — Air Brakes Practice Test 2026
The Delaware CDL — Air Brakes knowledge test has ~25 questions, and you need ~20 correct (80%) to pass. Practice free with questions written from the official Delaware 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 Delaware written test
The Delaware CDL — Air Brakes knowledge test has ~25 questions; you need ~20 correct (80%) to pass.
Based on the official Delaware 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 Delaware practice questions.
How to pass the first time
- Read the official Delaware 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.
Delaware CDL — Air Brakes test — frequently asked questions
How many questions are on the Delaware CDL — Air Brakes test?
The Delaware 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 Delaware 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 Delaware 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 Delaware 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 Delaware 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 Delaware driver handbook, practice by topic to target weak areas, and finish with full-length tests until you consistently pass.
Other Delaware practice tests
Take the CDL — Air Brakes test in another state
Every Delaware question is written from the official Delaware 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
Delaware CDL — Air Brakes questions with answers
20 sample questions from the Delaware 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. Which of these is NOT one of the four parts of the air brake check on Delaware's CDL vehicle inspection test?
Correct answer: A brake drum temperature test
The four parts are the air gauge and governor cutoff check, the air leakage rate test, the air warning device test and the emergency brake test. Failing to explain and demonstrate all four correctly is an automatic failure of the inspection test.
Source: Delaware Commercial Driver's Manual — Section 11.1.2, Air Brake or Hydraulic Brake Check
2. In stab braking, you let off the brakes when the wheels lock. How long can it take before the wheels are rolling again?
Correct answer: As much as one second
The wheels can need as long as a second to begin turning after the brakes are released. Braking again before they roll keeps the vehicle from straightening out.
Source: Delaware Commercial Driver's Manual — Section 5.4.3, Emergency Stops
3. Step 2 of the inspection adds one air brake item when the compressor runs off a belt. What do you look at?
Correct answer: Its condition and how tight it is
With a belt-driven compressor, the manual has you look at the belt's condition and tightness as part of Step 2, the engine compartment checks.
Source: Delaware Commercial Driver's Manual — Section 5.3.1, During Step 2 Engine Compartment Checks
4. A coworker claims that ABS always makes a truck stop in a shorter distance. What does the manual say?
Correct answer: Not necessarily; what ABS does is help you keep control when you brake hard
ABS is an add-on to the normal brakes. It leaves your normal braking ability unchanged and may or may not shorten a stop, but it keeps wheels from locking so the vehicle stays controllable.
Source: Delaware Commercial Driver's Manual — Section 5.1.16, Antilock Braking Systems (ABS)
5. A bus has dual parking control valves. Which one is used to set the spring brakes for parking?
Correct answer: The push-pull valve
One of the two valves is a push-pull control for parking. The other is spring-loaded and, while held in, uses air from a separate tank to release the spring brakes so the bus can be moved in an emergency.
Source: Delaware Commercial Driver's Manual — Section 5.1.15, Parking Brake Controls
6. For the L restriction on a CDL, what does the manual count as 'air brakes'?
Correct answer: Any brake system that works wholly or partly on the air brake principle
For both the skills test and the L restriction, a braking system counts as air brakes whether it runs fully or only partly on air. That is why a vehicle with air over hydraulic brakes still calls for the air brakes knowledge test.
Source: Delaware Commercial Driver's Manual — Section 1, CDL Endorsements & Restrictions
7. You brake hard on a slick road in a rig without ABS, and wheels other than your steering wheels lock up. What does the manual say can happen?
Correct answer: The vehicle may skid, jackknife or even spin
Locked steering wheels cost you steering control. When the other wheels lock, the result can be a skid, a jackknife or a spin.
Source: Delaware Commercial Driver's Manual — Section 5.4.2, Braking with Antilock Brakes
8. In the emergency brake test on a tractor pulling an air-operated trailer, when should the trailer-side valves pop out compared with the tractor's own valve?
Correct answer: At the same time as the tractor's valve, or before it
The tractor protection valve and the trailer's parking or emergency brake valve should close together with, or ahead of, the valve for the truck, tractor or bus.
Source: Delaware Commercial Driver's Manual — Section 11.1.2, Air Brake or Hydraulic Brake Check
9. Once you are in the right low gear on a long downgrade, how hard does the manual say to press the brakes each time you apply them?
Correct answer: Firmly enough that you can clearly feel the vehicle slowing
Each application should produce a definite slowdown and bring you to about five mph under your 'safe' speed, after which you release the brakes.
Source: Delaware Commercial Driver's Manual — Section 5.4.6, Proper Braking Technique
10. Which vehicles does the manual say must have both emergency brakes and parking brakes?
Correct answer: All trucks, truck tractors and buses
Every truck, truck tractor and bus needs emergency and parking brakes, and they have to be held on mechanically because air can leak away over time. Spring brakes usually fill both roles.
Source: Delaware Commercial Driver's Manual — Section 5.1.14, Spring Brakes
11. A Delaware CDL carries a Z restriction. What is that driver not allowed to operate?
Correct answer: A CMV whose brakes work entirely on the air brake principle
The Z restriction, 'No Full Air Brake' on Delaware's list, goes to a driver who took the skills test in a vehicle with air over hydraulic brakes. That driver may not operate a CMV with a full air brake system.
Source: Delaware Commercial Driver's Manual — Section 1, CDL Endorsements & Restrictions
12. A pickup cuts across your lane with little warning, and your instinct is to hit the brakes. When does the manual call that a good response?
Correct answer: When you have enough room to stop and you brake correctly
Braking is the natural reaction and a sound one, provided the distance is there and the brakes are used properly, in a way that keeps the vehicle straight and still lets you turn.
Source: Delaware Commercial Driver's Manual — Section 5.4.3, Emergency Stops
13. For the air leakage rate test on Delaware's inspection test, you shut off the engine. What do you do with the key next?
Correct answer: Turn it back to 'on' or 'battery charge'
With the engine off, the key goes back to 'on' or 'battery charge'. You then release the parking brake, fully apply the foot brake and, once the gauge settles, hold it for one minute.
Source: Delaware Commercial Driver's Manual — Section 11.1.2, Air Brake or Hydraulic Brake Check
14. Using the manual's downgrade braking technique, when do you apply the brakes again after releasing them?
Correct answer: When your speed has climbed back up to your 'safe' speed
You let the vehicle drift back up to the 'safe' speed, then brake it down to about five mph below that and release. The cycle repeats until the downgrade ends.
Source: Delaware Commercial Driver's Manual — Section 5.4.6, Proper Braking Technique
15. A modulating control valve lets the driver bring the spring brakes on gradually. Why does the manual say it works that way?
Correct answer: It gives the driver a controllable way to stop with the spring brakes after a service brake failure
The valve is spring-loaded to give a feel for the braking, and the farther the lever moves, the harder the spring brakes apply. That lets a driver stop under control when the service brakes are lost.
Source: Delaware Commercial Driver's Manual — Section 5.1.15, Parking Brake Controls
16. On Delaware's air brake check, the low air warning devices should activate before pressure falls under 55 psi or the level the manufacturer specifies. Whose job is it to know that manufacturer's figure?
Correct answer: The applicant's
It falls to the applicant to know the specifications for the test vehicle and describe them to the examiner.
Source: Delaware Commercial Driver's Manual — Section 11.1.2, Air Brake or Hydraulic Brake Check
17. Your low air warning is on, and you are driving a lightly loaded truck on a slippery road. What does the manual warn can happen if you keep going until the spring brakes apply on their own?
Correct answer: The truck may skid out of control
Spring brakes come on when pressure falls into the 20 to 45 psi range. On a light vehicle or a slick surface that can cause a skid, so the safer course is to stop while the foot brake still has air.
Source: Delaware Commercial Driver's Manual — Section 5.4.7, Low Air Pressure
18. In an air-operated disc brake, what turns the power screw?
Correct answer: The brake chamber pressing on the slack adjuster
Air disc brakes use a brake chamber and slack adjuster just as s-cam brakes do. When the chamber pushes on the slack adjuster, the power screw turns and clamps the disc between the caliper's pads.
Source: Delaware Commercial Driver's Manual — Section 5.1.8, Foundation Brakes
19. What does the manual mean by 'brake lag'?
Correct answer: The delay between pushing the pedal and the brakes actually working
Air has to travel through the lines before the brakes apply, so air brakes add a short delay that hydraulic brakes do not have. The distance covered in that delay is part of total stopping distance.
Source: Delaware Commercial Driver's Manual — Section 5.4.4, Stopping Distance
20. Why does the manual warn against walking away from your vehicle without setting the parking brakes or putting chocks under the wheels?
Correct answer: It could roll off and hurt someone or damage property
An unsecured vehicle can roll away. The manual's rule is to apply the parking brakes or chock the wheels whenever the vehicle is left unattended.
Source: Delaware Commercial Driver's Manual — Section 5.4.8, Parking Brakes