Air Brakes · Section 5.3

Inspecting air brakes: CDL practice questions

Section 5.3 covers the air brake checks you make during a vehicle inspection, in the order the manual gives them. The Air Brakes knowledge test asks about these checks, and the skills test asks you to do them.

Examlane has 30 questions on this chapter. Ten are below; open one to see the answer and why. The rest are in the practice tests.

Practice this chapter

1. Before you pull on the slack adjusters by hand, how should the vehicle be prepared?
1. On a slight hill, with the parking brakes on
2. On level ground, wheels chocked, parking brakes released
3. On level ground, parking brakes on, engine running
4. Anywhere safe, with the wheels free to roll
Answer: B. On level ground, wheels chocked, parking brakes released
Park on level ground and block the wheels so the vehicle cannot move, then release the parking brakes so the slack adjusters can move.
Based on: CDL manual, Section 5.3.2 (Georgia edition of the national model manual, read 2026-10-24). Question in our own words.
2. A slack adjuster probably needs adjustment if it moves more than about how far at the point where the push rod attaches?
1. About one quarter inch
2. About one half inch
3. About one inch
4. About three quarters of an inch
Answer: C. About one inch
When you pull hard, an adjuster that travels more than about an inch at the push rod probably needs adjusting.
Based on: CDL manual, Section 5.3.2 (Georgia edition of the national model manual, read 2026-10-24). Question in our own words.
3. What is a danger of too much brake slack?
1. The brakes grab too suddenly
2. The air compressor overheats
3. The spring brakes release by themselves
4. The vehicle can be very hard to stop
Answer: D. The vehicle can be very hard to stop
Brakes with too much slack work poorly, so the vehicle can be very hard to stop.
Based on: CDL manual, Section 5.3.2 (Georgia edition of the national model manual, read 2026-10-24). Question in our own words.
4. A vehicle has automatic slack adjusters that adjust on their own during full brake applications. How should you treat them at inspection?
1. Skip them, because they adjust themselves
2. Check them only after a brake problem
3. Check them at every inspection
4. Check them only at yearly inspections
Answer: C. Check them at every inspection
Automatic slack adjusters can still fail or be out of adjustment, so they must be checked like any other slack adjuster.
Based on: CDL manual, Section 5.3.2 (Georgia edition of the national model manual, read 2026-10-24). Question in our own words.
5. On a vehicle with automatic adjusters, the pushrod stroke goes past the legal adjustment limit. What does this indicate?
1. A fault in the adjuster, the brake parts, or its installation
2. The adjuster only needs a routine manual adjustment now and then
3. The brakes have simply worn in normally
4. The air compressor is producing too much pressure for the system
Answer: A. A fault in the adjuster, the brake parts, or its installation
A stroke beyond the legal limit on an automatic adjuster points to a mechanical problem or poor installation, not a need for routine adjusting.
Based on: CDL manual, Section 5.3.2 (Georgia edition of the national model manual, read 2026-10-24). Question in our own words.
6. Brakes with automatic adjusters are found out of adjustment. What is the recommended action?
1. Adjust them by hand every time and keep driving
2. Keep driving and recheck at the next inspection
3. Replace the air compressor
4. Get the vehicle to a repair shop at the earliest chance
Answer: D. Get the vehicle to a repair shop at the earliest chance
A brake with an automatic adjuster that is out of adjustment has an underlying fault, so the vehicle should be repaired promptly.
Based on: CDL manual, Section 5.3.2 (Georgia edition of the national model manual, read 2026-10-24). Question in our own words.
7. Why is manually adjusting an automatic slack adjuster dangerous?
1. It always makes the brakes grab too hard
2. It can give the driver a false sense of safety
3. It can turn off the antilock system on that wheel
4. It lets air leak out of the spring brake chambers
Answer: B. It can give the driver a false sense of safety
Hand adjustment usually hides the real problem, so the driver may wrongly believe the brakes are working well.
Based on: CDL manual, Section 5.3.2 (Georgia edition of the national model manual, read 2026-10-24). Question in our own words.
8. A brake drum crack is too long when it is longer than what?
1. A quarter of the friction area's width
2. Three quarters of the friction area's width
3. Half of the friction area's width
4. The friction area's entire width
Answer: C. Half of the friction area's width
A drum or disc is unsafe if a crack runs longer than half of the friction area's width.
Based on: CDL manual, Section 5.3.2 (Georgia edition of the national model manual, read 2026-10-24). Question in our own words.
9. Which condition means brake linings are unsafe?
1. Soaked with oil or grease
2. Covered in light brake dust
3. Slightly darker than when new
4. Warm after a recent stop
Answer: A. Soaked with oil or grease
Linings that are oil- or grease-soaked, loose, or dangerously thin cannot brake safely.
Based on: CDL manual, Section 5.3.2 (Georgia edition of the national model manual, read 2026-10-24). Question in our own words.
10. With the engine at operating rpms, a dual air system should build pressure through which range within 45 seconds?
1. 20 to 45 psi
2. 50 to 90 psi
3. 100 to 125 psi
4. 85 to 100 psi
Answer: D. 85 to 100 psi
Pressure in a dual air system should rise from 85 psi to 100 psi in 45 seconds or less, with the engine at operating rpm.
Based on: CDL manual, Section 5.3.3 (Georgia edition of the national model manual, read 2026-10-24). Question in our own words.

Read the chapter itself in your state's CDL manual, Section 5.3. Your state's manual is free: find it in the state table.

More Air Brakes chapters: Air brake system parts.