CDL AIR BRAKE PRACTICE STUDY
GUIDE 2026 COMPLETE QUESTIONS
AND VERIFIED ANSWERS
◉ Why drain water from the compressed air tanks? Answer: To prevent
fouling the air compressor oil and to avoid brake failure due to freezing
in cold weather.
◉ What is the maximum allowable leak rate for the air brake system?
Answer: The air brake system for a straight truck or bus should not leak
at a rate of more than 2 psi per minute with the engine off and the brakes
released.
◉ How to make an emergency stop using air brakes? Answer: Use the
stab braking method: brake hard until the wheels lock, then release the
brakes for as much time as the wheels were locked.
◉ How do you know your brakes are fading? Answer: You have to press
the brake pedal harder to control speed on a downgrade.
◉ What keeps air in the tanks if the air compressor develops a leak?
Answer: The one way check valve.
◉ How to check brake slack on S-cam brakes? Answer: Park on level
ground, chock the wheels, and release the parking brakes.
, ◉ What does the application pressure gauge show? Answer: It shows
how much pressure you have when you are applying to the brakes.
◉ At what psi do spring brakes engage? Answer: Spring brakes will
engage when air pressure drops below 60 psi.
◉ At what psi is the safety valve set to reduce pressure? Answer: The
safety valve is set to automatically reduce pressure at 150 psi.
◉ What happens if one system of a dual air system loses pressure?
Answer: Either the front or back brake will not be fully operational.
◉ How long should it take for air pressure to build from 85 to 100 psi?
Answer: It should take no longer than 45 seconds.
◉ What holds back the spring brakes during normal driving? Answer:
Air pressure holds back the spring brakes.
◉ At what psi does the air compressor stop pumping air? Answer: The
air compressor stops pumping air at 125 psi.
◉ What warning must the driver see before service air tank pressure
falls? Answer: The driver must see a warning before pressure falls below
55 psi.
GUIDE 2026 COMPLETE QUESTIONS
AND VERIFIED ANSWERS
◉ Why drain water from the compressed air tanks? Answer: To prevent
fouling the air compressor oil and to avoid brake failure due to freezing
in cold weather.
◉ What is the maximum allowable leak rate for the air brake system?
Answer: The air brake system for a straight truck or bus should not leak
at a rate of more than 2 psi per minute with the engine off and the brakes
released.
◉ How to make an emergency stop using air brakes? Answer: Use the
stab braking method: brake hard until the wheels lock, then release the
brakes for as much time as the wheels were locked.
◉ How do you know your brakes are fading? Answer: You have to press
the brake pedal harder to control speed on a downgrade.
◉ What keeps air in the tanks if the air compressor develops a leak?
Answer: The one way check valve.
◉ How to check brake slack on S-cam brakes? Answer: Park on level
ground, chock the wheels, and release the parking brakes.
, ◉ What does the application pressure gauge show? Answer: It shows
how much pressure you have when you are applying to the brakes.
◉ At what psi do spring brakes engage? Answer: Spring brakes will
engage when air pressure drops below 60 psi.
◉ At what psi is the safety valve set to reduce pressure? Answer: The
safety valve is set to automatically reduce pressure at 150 psi.
◉ What happens if one system of a dual air system loses pressure?
Answer: Either the front or back brake will not be fully operational.
◉ How long should it take for air pressure to build from 85 to 100 psi?
Answer: It should take no longer than 45 seconds.
◉ What holds back the spring brakes during normal driving? Answer:
Air pressure holds back the spring brakes.
◉ At what psi does the air compressor stop pumping air? Answer: The
air compressor stops pumping air at 125 psi.
◉ What warning must the driver see before service air tank pressure
falls? Answer: The driver must see a warning before pressure falls below
55 psi.
