Oregon CDL — Air Brakes Exam Simulation
25 questions · 20 correct to pass. You won't see any feedback until you finish — just like the real test.
Oregon CDL — Air Brakes questions with answers
20 sample questions from the Oregon CDL — Air Brakes question bank — each with the correct answer, a short explanation, and the section of the official handbook it comes from.
1. On most air-brake vehicles, a visible low-air warning must come on before tank pressure drops under:
Correct answer: 55 psi
A warning you can see is required and must appear before the tanks fall below 55 psi (or half the governor cut-out on older vehicles).
Source: Section 5.1.11 - Low Air Pressure Warning
2. If you need steadily more application pressure just to hold the same speed on level ground, the brakes are most likely:
Correct answer: fading
Rising application pressure to keep one speed is a sign of brake fade; the driver should ease off, slow down, and shift to a lower gear.
Source: Section 5.1.10 - Application Pressure Gauge
3. Compared with the near-instant action of hydraulic brakes, air brakes need roughly how long for pressure to reach the brakes?
Correct answer: Half a second or more
Air brakes have a built-in lag of about a half second or more because the air has to move through the lines before the brakes engage.
Source: Section 5.4.4 - Stopping Distance
4. Truck tractors with air brakes must be equipped with antilock brakes if built on or after:
Correct answer: March 1, 1997
Air-brake truck tractors made on or after March 1, 1997 are required to have ABS.
Source: Section 5.1.16 - Antilock Braking Systems (ABS)
5. To set the parking brakes on a newer air-brake vehicle, you:
Correct answer: pull the yellow diamond-shaped knob out
Newer trucks use a yellow, diamond-shaped push-pull knob; pulling it out applies the spring parking brakes and pushing it in releases them.
Source: Section 5.4.8 - Parking Brakes
6. Why can a heavily loaded vehicle take a long distance to stop once the spring brakes apply on their own?
Correct answer: The spring brakes do not act on every axle
Spring brakes are not on all axles, so a loaded vehicle stops poorly with them alone; that is why you stop earlier while foot brakes still work.
Source: Section 5.4.7 - Low Air Pressure
7. Brake linings should be replaced when they are:
Correct answer: soaked with oil or grease, or dangerously thin
Linings must not be loose, oil- or grease-soaked, or worn dangerously thin, and mechanical parts must not be broken or missing.
Source: Section 5.3.2 - Check Brake Drums, Linings, and Hoses
8. Where should you look for a trailer's ABS malfunction lamp?
Correct answer: On the left side, at a front or rear corner
Trailer ABS malfunction lamps are yellow and located on the left side, either at the front or rear corner.
Source: Section 5.1.16 - Antilock Braking Systems (ABS)
9. What is the main job of the air compressor?
Correct answer: To pump air into the storage tanks
The compressor, driven off the engine by gears or a belt, forces air into the storage tanks (reservoirs) that feed the brakes.
Source: Section 5.1.1 - Air Compressor
10. Air brakes add which element to total stopping distance that hydraulic brakes do not have?
Correct answer: Brake lag distance
Total stopping distance for air brakes is perception plus reaction plus brake lag plus braking distance; brake lag is the extra factor.
Source: Section 5.4.4 - Stopping Distance
11. Front brake limiting valves were installed on some vehicles built before which year?
Correct answer: 1975
Some vehicles made before 1975 have a front brake limiting valve and a cab control; keeping it in the normal position gives full stopping power.
Source: Section 5.1.13 - Front Brake Limiting Valve
12. How do you check that the parking brake will actually hold?
Correct answer: Set it, then gently try to pull forward in a low gear
With the parking brake on, easing forward against it in a low gear confirms it can keep the vehicle in place.
Source: Section 5.3.3 - Test Parking Brake
13. If the low-air pressure warning activates while you are driving, you should:
Correct answer: stop and safely park as soon as you can
A low-air warning may mean a leak. Controlled braking only works while air remains, so stop and park while you still have foot brakes.
Source: Section 5.4.7 - Low Air Pressure
14. When you pull hard on a manual slack adjuster, roughly how much movement suggests it needs adjustment?
Correct answer: More than about one inch
If the slack adjuster moves more than roughly an inch where the push rod attaches, it likely needs adjusting.
Source: Section 5.3.2 - Check Slack Adjusters
15. On large buses, low-pressure warning devices commonly signal at about:
Correct answer: 80 to 85 psi
It is common for the low-pressure warning on large buses to activate earlier, around 80 to 85 psi.
Source: Section 5.1.11 - Low Air Pressure Warning
16. Which foundation brake design is found most often at each wheel of an air-brake vehicle?
Correct answer: The s-cam drum brake
Foundation brakes sit at every wheel, and the s-cam drum type is by far the most common. Wedge and disc designs exist but are seen less often.
Source: Section 5.1.8 - Foundation Brakes
17. For an average driver at 55 mph in good conditions, the total stopping distance with air brakes is about:
Correct answer: over 450 feet
Adding perception, reaction, brake lag, and braking distance, the total at 55 mph comes to more than 450 feet.
Source: Section 5.4.4 - Stopping Distance
18. Air-brake trucks, buses, trailers, and converter dollies must have ABS when built on or after:
Correct answer: March 1, 1998
Other air-brake vehicles, including trucks, buses, trailers, and converter dollies, are required to have ABS if built on or after March 1, 1998.
Source: Section 5.1.16 - Antilock Braking Systems (ABS)
19. Before walking away from a truck you will leave unattended, the handbook requires you to:
Correct answer: apply the parking brakes or chock the wheels
An unattended vehicle can roll away and cause harm, so you must set the parking brakes or block the wheels before leaving it.
Source: Section 5.4.8 - Parking Brakes
20. After you release the brakes during stab braking, the wheels can take how long to begin rolling again?
Correct answer: Up to one second
It can take as much as a second for the wheels to start turning; re-applying before they roll keeps the vehicle from straightening out.
Source: Section 5.4.3 - Emergency Stops