Oklahoma CDL — Air Brakes practice
Oklahoma CDL — Air Brakes: Safe Driving Practices practice test
Following distance, scanning, blind spots, using your lights, and the habits that prevent crashes and keep you in control.
Content reviewed against official driver handbooks · August 12, 2026
13 questions · pass with 10 correct. You get instant feedback and an explanation after every answer.
Study questions with answers
12 sample Safe Driving Practices questions with the correct answer, a short explanation, and the official handbook reference. Read through them, then take the quiz above.
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1. What is the job of an alcohol evaporator in some air brake systems?
Correct answer: To reduce the risk of ice forming in the valves in cold weather
By feeding alcohol into the system, the evaporator lowers the chance of ice forming in air brake valves and other parts during cold weather, since ice can keep the brakes from working.
Source: Section 5.1.5 - Alcohol Evaporator
2. Why is it important to drain the air storage tanks completely?
Correct answer: To clear out water and oil that harm the system and can freeze
Compressed air carries water and a little compressor oil that settle at the bottom of the tank; the water can freeze in cold weather and cause the brakes to fail, so the tanks must be emptied fully.
Source: Section 5.1.4 - Air Tank Drains
3. Which statement about slack adjusters on vehicles built since 1994 is accurate?
Correct answer: They are automatic but still have to be checked
Every vehicle made since 1994 uses automatic slack adjusters; even though they self-adjust during full brake applications, the driver still has to inspect them.
Source: Section 5.3.2 - Walk-around Inspection
4. Why is working the brake pedal up and down when you do not need to slow down a bad habit?
Correct answer: It bleeds air off faster than the compressor can put it back, and the brakes quit once pressure gets too low
Every time you let the pedal up, some air leaves the system. Fanning the pedal for no reason empties the tanks quicker than the compressor can refill them, and once pressure sinks far enough you have no brakes.
Source: Section 5.1.7 - The Brake Pedal
5. Among foundation brakes, which design is the most widely used?
Correct answer: The s-cam drum brake
Foundation brakes sit at every wheel, and the s-cam drum brake is by far the most common; wedge and disc types are far less common.
Source: Section 5.1.8 - Foundation Brakes
6. How is the air compressor usually driven by the engine on an air brake vehicle?
Correct answer: Through gears or a v-belt
The compressor takes its power from the engine, linked either through a set of gears or by a v-belt.
Source: Section 5.1.1 - Air Compressor
7. During the engine compartment step of the inspection, what extra air brake item should you check on a belt-driven compressor?
Correct answer: The condition and tightness of the compressor drive belt
When the compressor runs off a belt, the inspection adds a check of that belt's condition and tension; it should be in good shape.
Source: Section 5.3.1 - Engine Compartment Checks
8. On air-operated disc brakes, what component does the job that an s-cam does on drum brakes?
Correct answer: A power screw that pinches the rotor between the caliper's lining pads
Disc brakes still use a brake chamber and a slack adjuster, but the slack adjuster rotates a power screw, and that screw pinches the rotor between the lining pads of a caliper the way a big clamp would.
Source: Section 5.1.8 - Foundation Brakes
9. You are braking hard in a combination where antilock brakes are fitted to the tractor but not the trailer. What should you be watching for?
Correct answer: The trailer swinging out, which calls for easing off the brakes when you can do it safely
ABS on the tractor alone should preserve your steering and cut the odds of a jackknife, but the manual still tells you to watch the trailer and, when it is safe to do so, come off the brakes if the trailer starts to swing.
Source: Section 5.4.2 - Braking with Antilock Brakes
10. What advantage do the air storage tanks give you if the compressor quits pumping?
Correct answer: Enough compressed air is still on hand to apply the brakes a number of times
The reservoirs hold a supply of compressed air, and the manual notes there is normally enough of it left for a number of brake applications even after the compressor has stopped working.
Source: Section 5.1.3 - Air Storage Tanks
11. After you have selected the correct low gear for a long downgrade, how should you use the service brakes?
Correct answer: Squeeze hard enough to feel a clear drop in speed, then let off once you are roughly five mph under your safe speed
On a grade the brakes only back up the engine's braking effect. Squeeze until the truck noticeably slows, hold roughly three seconds until you are about five mph under your safe speed, release, then repeat once the speed builds back up.
Source: Section 5.4.6 - Proper Braking Technique
12. If a truck's air compressor carries its own separate oil supply, what should the driver do before setting out?
Correct answer: Check the compressor's oil level
A compressor that holds its own oil, rather than being lubricated by engine oil, needs its oil level checked before you drive.
Source: Section 5.1.1 - Air Compressor
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