Using Air Brakes Practice Questions
A loaded truck does not stop the way anything else you have driven stops. The weight is behind you, the brakes are spread across axles that are not all carrying the same share of it, and the drums doing the work turn every stop into heat they then have to get rid of. This part of the air brakes test is not about valves and governors. It is about what your right foot does when the grade is long, when the wheels lock, or when the trailer starts coming up beside you, and it is the part you will actually use.
5 questions, 4 right to pass. Free, untimed, no account.
Correct · A
At roughly what air tank pressure does the governor stop the compressor from pumping any more air?
- About 125 psi Correct answer
- About 100 psi
- About 150 psi
- About 55 psi
Texas Commercial Motor Vehicle Drivers Handbook, 5.1.2 Air Compressor Governor, p. 5-1
Using air brakes on the road practice test: quick facts
What this practice test does. Your state's own numbers are cited separately.
- Questions per test
- 5
- Right answers to pass
- 4
- Time limit
- None
- Cost
- FreeNo account, no card, no limit on retries
- Questions in the bank
- 65Drawn fresh every time you start
- Every answer cited
- YesDocument, section and page on each one
- Last reviewed
- September 2026Re-checked against the source once a year
- Written from
- Texas Commercial Motor Vehicle Drivers Handbook
What this test covers
Every subject below has cited questions behind it. The number is how many are in the bank right now, and each draw is weighted across them.
- Air brake systems 65
How hard the bank is
Every test you start pulls a mix, so you get the easy marks and the ones people actually fail on.
- Straightforward 15
- Moderate 35
- Hard 15
Sample Using air brakes on the road questions
Real questions from the bank, with the answer and the page it came from. Open a few, then take the test properly.
At roughly what air tank pressure does the governor stop the compressor from pumping any more air?
- About 125 psi
- About 100 psi
- About 150 psi
- About 55 psi
Cut-out is around 125 psi. That is where the governor takes the compressor off load and the needle stops climbing. 100 psi is the cut-in figure, 150 psi is where the safety relief valve opens, and 55 psi is the low air warning. Confusing cut-out with cut-in is the classic mistake.
Tank pressure has been dropping as the brakes are used. At about what pressure will the governor let the compressor start pumping again?
- About 100 psi
- About 125 psi
- About 85 psi
- About 55 psi
Cut-in is around 100 psi, cut-out around 125 psi, so the system normally cycles between those two figures. 85 psi is the bottom of the pressure build-up test range and 55 psi is where the low air warning must already have come on.
An air compressor has its own oil supply rather than being lubricated by engine oil. What does that add to the driver's routine?
- Check the compressor oil level before driving
- Drain the compressor at the end of each day of driving
- Top the compressor up with alcohol in cold weather
- Nothing, because the engine oil check already covers it
A compressor with its own oil supply has to have that level checked before driving. Draining at the end of the day is the air tank routine, and the alcohol top-up belongs to the alcohol evaporator, not the compressor.
A governor is not cutting the compressor in and out at the pressures the manufacturer specifies. Why does that have to be fixed before the vehicle goes out?
- It may not keep enough air pressure in the tanks for safe driving
- It stops the brake lights from coming on when the pedal is pushed
- It disables the low air pressure warning signal
- It makes the spring brakes release on their own
The governor is what keeps a working reserve in the tanks. If it cuts in and out at the wrong pressures the reserve may never be there when it is needed. The stop light switch and the low air warning are separate devices, and nothing about a faulty governor releases spring brakes.
The air tanks on a truck have manually operated drain valves. How often does the driver have to drain them?
- At the end of each day of driving
- Once a week
- Before the start of each trip, but not afterwards
- Only when the low air pressure warning comes on
Manual drain valves are the driver's job at the end of every driving day, by a quarter turn or a pull cable, and the tank has to be drained completely. Only automatic drain valves take that job away, and even then the alcohol evaporator still needs checking in cold weather.
Why does the water that collects in the bottom of an air tank matter most in cold weather?
- It can freeze and cause the brakes to fail
- It thins the compressor oil so the compressor seizes
- It sets off the low air pressure warning while driving
- It makes the safety relief valve open below its setting
Compressed air carries water and a little compressor oil, both of which settle in the bottom of the tank. In freezing weather that water can turn to ice and take the brakes out altogether, which is why the tank is drained completely rather than just cracked open.
At about what pressure is the safety relief valve on the first air tank usually set to open?
- 150 psi
- 125 psi
- 100 psi
- 55 psi
The safety relief valve sits in the first tank the compressor pumps to and is usually set for 150 psi, well above the governor's 125 psi cut-out. If it is venting, pressure has gone somewhere it should never reach.
Air is escaping from the safety relief valve on the first air tank. What should the driver do about it?
- Treat it as a fault and have a mechanic repair it
- Nothing, since that is how the valve holds pressure steady
- Drain the tank down and carry on driving
- Reset the governor cut-out setting to a lower pressure
The safety valve is a last line of defence, not a regulator. Air coming out of it means something in the system is letting pressure rise too far, and that is a mechanic's job. Draining the tank or moving the governor setting hides the fault instead of fixing it.
How to use this test
-
Take it cold, once
Do not revise first. You want to know which subjects are actually weak, and a clean run tells you that in ten minutes.
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Read the reason, not the score
The explanation for each answer opens on the next page with its handbook page. That is the bit that makes it stick.
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Retry only what you missed
The result page has a button for exactly that. Far faster than sitting the whole thing again.
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Come back on another day
A different draw each time exposes different gaps. Two runs a week beats ten in one evening.
Why this one is different
You can check every answer
Document, section and page on all of them, plus the date it was read. Nothing goes live without all four.
Nothing is behind a paywall
Every question in the bank is free, every time. There is no premium tier holding the hard ones back.
Scored by subject
You find out which topic is costing you marks, not just a number out of 5.
More about this test
Two emergency methods, and the one exception
There are two ways to stop hard without losing the vehicle, and the test wants you to tell them apart. Controlled braking means braking as hard as you can without locking the wheels, and keeping your steering movements very small while you do it. If a wheel locks, or you need a bigger steering correction than that, you release and start again. Stab braking is the other one: full application, release the instant the wheels lock, then full application again as soon as the wheels start rolling.
That last bit is where people lose the question. After you release, it can take up to a second before the wheels turn again, and a second feels like a long time when something is in front of you. Get back on the brakes before they are rolling and the vehicle cannot straighten out, because locked wheels do not steer. Wait for the roll, then stab again.
The only case where you simply put the pedal to the floor is a vehicle you always drive that has working ABS on every axle. Not the tractor only. Not the trailer only. Partial ABS still helps you, but it does not earn the full application, and the half you are missing is the half you have to watch. Brake hard in a combination where only the tractor has ABS and the trailer starts to swing, and the answer is to ease off the brakes if it is safe to do so. Braking harder will not pull it back into line.
Why brakes fade, and why you come off them
On a long grade you are in the proper low gear first, and the brakes are there to take back the speed the hill keeps giving you. The method is to apply hard enough to feel a definite slowdown, hold it until you are about 5 mph below your safe speed, then release completely and let the speed build back up before you do it again. Drivers who come off as soon as they feel the slowdown end up braking almost continuously, which is exactly how drums cook.
Two things go wrong when they do. The lining changes chemically and loses friction, and the drum expands away from the shoes. So the shoes now have to travel further to touch the drum at all, and when they touch they press with less force. Each application achieves less than the one before it, which is why fade gets worse rather than levelling off. It is a different thing from brake lag, which is the delay before air-applied brakes take hold in the first place.
When you stop
Brakes that have just come down a long grade are very hot, and setting the parking brakes on hot brakes can damage them. Chock the wheels on a level surface and let them cool first. The opposite problem is very wet brakes in freezing weather, which can freeze on. Those you dry out by braking lightly in a low gear as you drive.
If air is escaping and you cannot stop it, stop the vehicle on the foot brake while the air lasts. Do not wait for the spring brakes to do it for you. They are not fitted to every axle, so a heavy load ends up being stopped by only some of the brakes and rolls a long way, and a light one can skid out of control when they snap on.
And whatever the state of the brakes, a vehicle is never left unattended without the parking brakes set or the wheels chocked, however short the errand.
Also worth reading
Last reviewed September 2026. Sources are re-checked against their publishers once a year.
Questions about this test
What is the difference between stab braking and controlled braking?
Should I pump the brakes going down a long hill?
Does ABS let me just stand on the brake pedal?
Does ABS shorten my stopping distance?
Is brake fade the same thing as brake lag?
Why can I not set the parking brakes after a long downgrade?
My trailer swings out when I brake hard. What do I do?
Still not sure?
Every question names the document and page behind it, so a wrong answer is something you can prove rather than argue about.
Other tests to take
- Chambers, slack adjusters and drums 4 questions, 3 to pass
- Compressor and governor 4 questions, 3 to pass
- Dual air systems 4 questions, 3 to pass
- Air brake inspection and leak tests 4 questions, 3 to pass
- Brake lag and stopping distance 4 questions, 3 to pass
- Spring and parking brakes 5 questions, 4 to pass
- Tanks, valves and lines 4 questions, 3 to pass
Ready when you are.
5 questions drawn fresh from 65 cited ones. No account, nothing to pay, and every question in the bank is free.