CDL AIR BRAKE PRACTICE TEST
2026 COMPLETE QUESTIONS AND
VERIFIED ANSWERS
◉ When should parking brakes be used in air brake vehicles? Answer:
Anytime the vehicle is parked.
◉ What should you do if your antilock braking system is not working?
Answer: Drive normally, but get the system serviced soon.
◉ What can excessive use of the service brakes lead to? Answer:
Expansion of the brake drums.
◉ What should you do if a low air pressure warning comes on for only
one system? Answer: Stop and safely park. Continue only after the
system is fixed.
◉ At what psi should the air compressor stop pumping? Answer: 130
psi.
◉ What is the use of air brakes on a downgrade? Answer: It is only a
supplement to the braking effect of the engine.
◉ How long should it take for air pressure to build from 85-100 psi?
Answer: 45 seconds.
,◉ What can you do with dual parking control valves? Answer: Use
pressure from a separate tank to release the spring emergency parking
brakes to move a short distance.
◉ What is the proper method of braking when going down long and/or
steep grades? Answer: Brake until your speed is about 5 mph below
your 'safe' speed, and then release your brakes.
◉ What is the minimum thickness for brake drums or discs? Answer:
1/4 inch.
◉ What does a supply pressure gauge tell you? Answer: How much
pressure is in the air tanks.
◉ Why does air braking take more time than hydraulic braking?
Answer: Air takes more time to flow through the lines than hydraulic
fluid.
◉ What holds spring brakes back during normal driving? Answer: Air
pressure.
◉ What may happen if you don't keep the alcohol evaporator filled?
Answer: Ice may form in the air storage tanks and cause the brakes to
fail.
,◉ What is the service brake system? Answer: The system that applies
and releases the brakes when the driver uses the brake pedal.
◉ What should you do to test air service brakes? Answer: Brake firmly
when slowly moving forwards.
◉ How do you know your brakes are fading? Answer: You have to push
the brake pedal harder to control speed on a downgrade.
◉ What is the maximum leak rate for the air brake system of a straight
truck or bus? Answer: 2 psi per minute with the engine off and the
brakes released.
◉ What does the braking power of the spring brakes depend on?
Answer: The service brakes being in adjustment.
◉ What should you do if one system of a dual air brake system is low on
pressure? Answer: Either the front or rear brakes will not be fully
operational.
◉ What can legally hold the parking or emergency brakes of trucks and
buses? Answer: Spring pressure.
◉ What are the three different systems combined in modern air brake
systems? Answer: Service, parking, and emergency brakes.
, ◉ What does the air supply pressure gauge show? Answer: How much
pressure is in the air tanks.
◉ How should you brake in an emergency? Answer: Brake so you can
steer and your vehicle stays in a straight line.
◉ What should you do if your vehicle has an alcohol evaporator?
Answer: Check and fill the alcohol level every day during cold weather.
◉ How much does the air brake lag distance add at 55 mph on dry
pavement? Answer: 32 feet to your stopping distance.
◉ At what psi will the spring brakes on tractors and straight trucks bring
your truck to a stop? Answer: 20 psi.
◉ What happens when you apply the brakes? Answer: The brake
shoes/linings are pressed against the brake drum.
◉ What is the most important thing to do when a low air pressure
warning comes on? Answer: Stop and safely park as soon as possible.
◉ What is the air loss rate for a straight truck or bus with the engine off
and the brakes on? Answer: Should not be more than 3 psi in one
minute.
2026 COMPLETE QUESTIONS AND
VERIFIED ANSWERS
◉ When should parking brakes be used in air brake vehicles? Answer:
Anytime the vehicle is parked.
◉ What should you do if your antilock braking system is not working?
Answer: Drive normally, but get the system serviced soon.
◉ What can excessive use of the service brakes lead to? Answer:
Expansion of the brake drums.
◉ What should you do if a low air pressure warning comes on for only
one system? Answer: Stop and safely park. Continue only after the
system is fixed.
◉ At what psi should the air compressor stop pumping? Answer: 130
psi.
◉ What is the use of air brakes on a downgrade? Answer: It is only a
supplement to the braking effect of the engine.
◉ How long should it take for air pressure to build from 85-100 psi?
Answer: 45 seconds.
,◉ What can you do with dual parking control valves? Answer: Use
pressure from a separate tank to release the spring emergency parking
brakes to move a short distance.
◉ What is the proper method of braking when going down long and/or
steep grades? Answer: Brake until your speed is about 5 mph below
your 'safe' speed, and then release your brakes.
◉ What is the minimum thickness for brake drums or discs? Answer:
1/4 inch.
◉ What does a supply pressure gauge tell you? Answer: How much
pressure is in the air tanks.
◉ Why does air braking take more time than hydraulic braking?
Answer: Air takes more time to flow through the lines than hydraulic
fluid.
◉ What holds spring brakes back during normal driving? Answer: Air
pressure.
◉ What may happen if you don't keep the alcohol evaporator filled?
Answer: Ice may form in the air storage tanks and cause the brakes to
fail.
,◉ What is the service brake system? Answer: The system that applies
and releases the brakes when the driver uses the brake pedal.
◉ What should you do to test air service brakes? Answer: Brake firmly
when slowly moving forwards.
◉ How do you know your brakes are fading? Answer: You have to push
the brake pedal harder to control speed on a downgrade.
◉ What is the maximum leak rate for the air brake system of a straight
truck or bus? Answer: 2 psi per minute with the engine off and the
brakes released.
◉ What does the braking power of the spring brakes depend on?
Answer: The service brakes being in adjustment.
◉ What should you do if one system of a dual air brake system is low on
pressure? Answer: Either the front or rear brakes will not be fully
operational.
◉ What can legally hold the parking or emergency brakes of trucks and
buses? Answer: Spring pressure.
◉ What are the three different systems combined in modern air brake
systems? Answer: Service, parking, and emergency brakes.
, ◉ What does the air supply pressure gauge show? Answer: How much
pressure is in the air tanks.
◉ How should you brake in an emergency? Answer: Brake so you can
steer and your vehicle stays in a straight line.
◉ What should you do if your vehicle has an alcohol evaporator?
Answer: Check and fill the alcohol level every day during cold weather.
◉ How much does the air brake lag distance add at 55 mph on dry
pavement? Answer: 32 feet to your stopping distance.
◉ At what psi will the spring brakes on tractors and straight trucks bring
your truck to a stop? Answer: 20 psi.
◉ What happens when you apply the brakes? Answer: The brake
shoes/linings are pressed against the brake drum.
◉ What is the most important thing to do when a low air pressure
warning comes on? Answer: Stop and safely park as soon as possible.
◉ What is the air loss rate for a straight truck or bus with the engine off
and the brakes on? Answer: Should not be more than 3 psi in one
minute.
