Free Indiana DMV CDL — Air Brakes Practice Test 2026
The Indiana CDL — Air Brakes knowledge test has ~25 questions, and you need ~20 correct (80%) to pass. Practice free with questions written from the official Indiana 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 Indiana written test
The Indiana CDL — Air Brakes knowledge test has ~25 questions; you need ~20 correct (80%) to pass.
Based on the official Indiana 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 Indiana practice questions.
How to pass the first time
- Read the official Indiana 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.
Indiana CDL — Air Brakes test — frequently asked questions
How many questions are on the Indiana CDL — Air Brakes test?
The Indiana 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 Indiana 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 Indiana 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 Indiana 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 Indiana 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 Indiana driver handbook, practice by topic to target weak areas, and finish with full-length tests until you consistently pass.
Other Indiana practice tests
Take the CDL — Air Brakes test in another state
Every Indiana question is written from the official Indiana 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
Indiana CDL — Air Brakes questions with answers
20 sample questions from the Indiana 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. When should you NOT set the parking brakes, and instead chock the wheels to hold the vehicle?
Correct answer: When the brakes are very hot from a steep grade, or very wet in freezing weather
Avoid the parking brakes when the brakes are very hot from a steep grade or very wet in freezing temperatures; use wheel chocks instead.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.4.8 Parking Brakes
2. When checking an s-cam slack adjuster by hand, how much movement suggests it needs adjustment?
Correct answer: More than roughly one inch at the pushrod attachment
If a slack adjuster moves more than about one inch where the pushrod attaches, it probably needs to be adjusted.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.3.2 Check Slack Adjusters on S-cam Brakes
3. When the low air warning first comes on while you are driving, what is the safest thing to do?
Correct answer: Pull over to a safe stop right away, while you still have brake control
Don't wait for the spring brakes to trip on their own; bring the vehicle to a safe stop while you can still control the brakes.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.14 Spring Brakes
4. On a long, steep downgrade, how should the service brakes be used relative to the engine?
Correct answer: Only as a supplement to the engine's braking, while in a proper low gear
On a steep grade the brakes should only supplement engine braking - be in a proper low gear and apply them in short intervals.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.4.6 Proper Braking Technique
5. Air-braked truck tractors are required to have antilock brakes if they were built on or after which date?
Correct answer: March 1, 1997
Truck tractors built on or after March 1, 1997 must have ABS; most other air brake vehicles are required to have it from March 1, 1998.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.16 Antilock Braking Systems (ABS)
6. On a newer air brake vehicle, how do you set the parking brakes?
Correct answer: Pull out the yellow, diamond-shaped push-pull knob
Newer vehicles use a yellow, diamond-shaped push-pull knob - pull it out to apply the parking brakes and push it in to release them.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.15 Parking Brake Controls
7. How often must a driver empty manually-operated air tank drain valves?
Correct answer: At the end of each driving day
Manual drain valves have to be opened by the driver at the close of each day of driving to clear out water and oil.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.4 Air Tank Drains
8. What is the point of a modulating control valve for the spring brakes?
Correct answer: To let you bring the spring brakes on gradually if the service brakes quit
A spring-loaded modulating valve lets you apply the spring brakes gradually so you can still slow down if the service brakes fail.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.15 Modulating Control Valves
9. Compared with hydraulic brakes, why do air brakes add 'brake lag' to the stopping distance?
Correct answer: It takes a half second or more for the air to reach the brakes through the lines
Unlike hydraulic brakes, which work instantly, air needs about a half second or more to travel through the lines to the brakes.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.4.4 Stopping Distance
10. How does an air brake system light up the brake lamps for drivers behind you?
Correct answer: Through an electric stop light switch that works off air pressure
An electric stop light switch, operated by air pressure, turns on the brake lights whenever you apply the brakes.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.12 Stop Light Switch
11. How do you check that the parking brake will actually hold?
Correct answer: Set the parking brake and tug against it gently in a low gear
Set the parking brake and gently pull against it in a low gear to confirm it holds the vehicle.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.3.3 Test Parking Brake
12. What happens as you press the brake pedal (the foot or treadle valve) down harder?
Correct answer: More air pressure is delivered to the brakes
Pushing the treadle valve down harder sends more air pressure to the brakes; easing off reduces the pressure and releases them.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.7 The Brake Pedal
13. Why is it a mistake to repeatedly pump and release the brake pedal for no reason?
Correct answer: It can drain air faster than the compressor replaces it, and low pressure means no brakes
Needless pumping bleeds air out faster than the compressor can rebuild it, and if pressure drops too low the brakes stop working.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.7 The Brake Pedal
14. Total stopping distance for an air brake vehicle is made up of which four parts?
Correct answer: Perception, reaction, brake lag, and braking distances
For air brakes the total is perception distance plus reaction distance plus brake lag distance plus braking distance.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.4.4 Stopping Distance
15. Why should you avoid pushing the brake pedal down while the spring brakes are already set?
Correct answer: The combined spring and air forces could damage the brakes
Applying the pedal on top of set spring brakes can combine the spring and air forces and damage the brakes.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.15 Parking Brake Controls
16. With the engine off and the parking brake released, the air loss on a single vehicle should stay under how much per minute?
Correct answer: Less than 2 psi
For a single vehicle the static leakage rate should be less than 2 psi in one minute; a combination is allowed less than 3 psi.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.3.3 Test Air Leakage Rate
17. What is the main cause of brake fade on a long downgrade?
Correct answer: Too much heat from overusing the service brakes instead of leaning on engine braking
Overusing the service brakes builds excessive heat that changes the linings and expands the drums, which cuts braking force.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.4.5 Brake Fading or Failure
18. At 55 mph on dry pavement, roughly how far does an average air brake vehicle travel before it fully stops?
Correct answer: More than 450 feet
Adding the brake lag (about 32 feet) to the other factors, the total stopping distance at 55 mph works out to more than 450 feet.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.4.4 Stopping Distance
19. What does a supply pressure gauge tell the driver?
Correct answer: How much air pressure is stored in the tanks
The supply pressure gauge shows how much air is currently stored in the tanks.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.9 Supply Pressure Gauges
20. What does ABS actually do for you during hard braking?
Correct answer: It helps you stay in control while braking hard, even if it does not shorten stopping distance
ABS helps you keep the vehicle under control during hard braking, though it does not necessarily shorten your stopping distance.
Source: Indiana Commercial Driver's License Manual, Section 5 (Air Brakes), 5.1.16 Antilock Braking Systems (ABS)