Safety & Compliance > CDL "Air Brakes" Practice Test Back to CDL Practice Tests Main Page 1. What are the three parts of an air brake system? a. Service brakes, emergency brakes and parking brakes b. Service brakes, emergency brakes and alternate brakes c. Safety brakes, parking brakes and emergency brakes d. Dual brakes, service brakes and emergency brakes 2. What does the emergency brake system do? a. In case of a vehicle fire, it supplies air to the automatic fire extinguishing system b. Uses parts of the service and parking system to stop the vehicle in case of a brake system failure c. Supplies a steady air pressure to the service brakes if they fail d. Acts as the parking brake when stopped. 3. If air pressure does not build up fast enough: a. Your pressure may drop too low during driving, requiring an emergency stop. b. You may not be able to release the spring brake. c. The low air warning buzzer will come on during the trip. d. It will have no effect on your stopping ability. 4. What does cut out mean as applied to the air compressor in the air brake system? a. When pressure builds to a sufficient level in the storage tank, the compressor cuts out and stops supplying air. b. On a belt driven compressor, cut out occurs when the belt is loose and begins to slip. c. The compressor will cut out when the brakes are applied. d. The term cut out has no application or relationship to the compressor. 5. Why should you drain the air tanks? a. So that the brake shoes do not remain in contact with the drums and freeze. b. So that the air pressure does not continue to keep pressure on the seals. c. To reduce moisture in the air system. d. To see if the drain valves work properly. 6. How often should you drain the air tanks? a. Whenever you change the oil in the engine. b. Once a week. c. Never, except before repairing the brakes. d. Once per day. 7. Why is alcohol added to the air in some air brake systems? a. Alcohol keeps the system lubricated. b. Alcohol helps prevent the system from freezing in cold weather. c. Alcohol keeps the seals and gaskets from leaking. d. You should never add alcohol to an air brake system. 8. After selecting the proper gear for a steep downgrade, you should: a. Apply the brakes just hard enough to feel a definite slowdown. b. When you are 5 mph below your "safe speed", release the brakes. c. When you reach your "safe speed" again, re-apply the brakes. d. All the above. 9. Emergency and parking brakes must be held on by mechanical force because: a. They won't freeze. b. Mechanical force does not require an evaporator. c. Air pressure can eventually leak away. d. All of the above. 10. What does the automatic front wheel limiting valve do? a. Limits the amount of air required to operate the front brakes. b. Limits the pedal pressure required to operate the front brakes. c. Limits the travel of the brake shoes on the front brakes. d. Reduces the air to the front brakes, except under hard braking. 11. In addition to perception, reaction and braking distance, total stopping time with an air brake system includes the following factor: a. Slippery conditions. b. Elevation. c. Brake lag distance. d. Percent of grade. 12. The air compressor governor will "cut in" at about ___ psi, and will "cut out" at about ___ psi: a. 100;125 b. 125;150 c. 60;30 d. 15;50 13. What are spring brakes? a. A special type of brake that is constructed from spring steel. b. For vehicles equipped with coil springs, an automatic stop to prevent coil collapse. c. The parking brake system on most vehicles equipped with air brakes. d. Brakes that are connected to the leaf spring system on each axle. 14. A dual parking control valve: a. Allows two people to apply the parking brake at the same time. b. Allows the driver to move the vehicle a short distance in an emergency. c. Applies the parking brake to two axles. d. None of the above. 15. At what air pressure will the safety relief valve open? a. 20-45 psi b. 60 psi c. 100 psi d. 150 psi 16. What is the proper way to determine free play in manual slack adjusters? a. Park on level ground and pull hard on the slack adjuster. b. Park on level ground, chock the wheels, release the parking brake and use a pry bar or gloved hand to pull hard on the slack adjuster. c. Park on level ground, chock the wheels, release the parking brakes and back out the adjusting nut on the slack adjuster to its stop. d. Park on level ground, chock the wheels, and use a pry bar or gloved hand to pull hard on the slack adjuster. 17. What is the maximum leakage rate for an air brake equipped combination vehicle? a. 5 psi per minute b. 0 psi per minute c. 3 psi per minute d. 8 psi per minute 18. If you have a service system failure, what happens? a. The service system is designed to retain enough air to stop the vehicle. b. The emergency system will stop the vehicle. c. The parking system will stop the vehicle. d. The brakes will not work and you cannot stop the vehicle. 19. What does the air supply pressure gauge do? a. Indicates how much air pressure is required to operate the service system. b. Indicates how much pressure you have used since starting the engine. c. Indicates how much air pressure there is in the holding tank(s). d. Indicates how much air pressure you need for safe operation. 20. At what air pressure does the low pressure warning signal activate? a. 20 psi b. 40 psi c. 60 psi d. 80 psi 21. What is the most popular type of brakes that modern commercial vehicles are equipped with? a. Disc b. Mechanical c. Hydraulic d. S-Cam 22. The braking power of the spring brake depends on: a. The driver's leg strength. b. The number of coils in the spring. c. The brakes being in correct adjustment. d. The size of the brake chamber. 23. How do spring brakes work? a. Air pressure holds back the spring and if the air pressure drops below the tension of the spring, the brakes are activated. b. The brake shoes are held against the drums with springs. c. The air release valves are held closed by special springs until the air pressure exceeds 45 psi and the valves open. 24. How do you test the service brake? a. Start the engine, move forward slowly and release the accelerator. b. Start the engine, wait for normal air pressure, move forward slowly, and apply the brakes. c. Release the parking brakes with the engine running. d. Use a pry bar or a gloved hand to pull hard on the slack adjuster. 25. When inspecting the brake drums during the pre-trip inspection, what should you look for? a. Check to insure the drums are perfectly round. b. Check for cracks in the drum. c. Check for the thickness of the drum. d. Check the width of the drum to make sure it matches the width of the brake shoe.   Oregon Trucking Associations, Inc. 4005 SE Naef Rd. | Portland, OR 97267 503.513.0005 | 503.513.0008 (fax) | 888-293-0005 | ortruck@ortrucking.org © 2004 Oregon Trucking Associations Inc.