Prepare for the CDL Air Brakes endorsement test with these practice questions and answers. This guide covers air brake components, brake inspection, and proper brake operation.
Q: When going down long or steep downgrades you should always..
Answer: use the braking effects of the engine.
Q: The application air gauge shows:
Answer: amount of pressure currently being applied by brake pedal
Q: The low air pressure warning will activate at approximately:
Answer: 60 psi
Q: If you experience a severe air loss and the service brake system is no longer working, which brake system is used to stop the vehicle?
Answer: emergency brake system
Q: Air tanks should be drained at least:
Answer: daily
Q: An alcohol evaporator:
Answer: injects alcohol into the air lines to help prevent freezing
Q: The air compressor governor determines:
Answer: the cut-in and cut-out pressure
Q: If you experience a sudden drop in the air system you should:
Answer: stop immediately when safe to do so
Q: At approximately 20-45 psi:
Answer: spring brakes will apply automatically
Q: Vehicles equipped with air brakes must have:
Answer: an air pressure gauge
Q: When a driver depresses the brake pedal, what air brake system is he using?
Answer: service brakes
Q: Emergency brakes are activated:
Answer: by a loss of air pressure
Q: Which of the following is the most common foundation brake found in commercial vehicles?
Answer: “S” cam drum
Q: If the air system ruptures, which of the following prevents the air from escaping out the system?
Answer: the one way check valve
Q: The spring brakes, or emergency braking system:
Answer: will work only if the brakes are adjusted properly
Q: A vehicle with a dual air system:
Answer: will only have one set of controls
Q: When driving down the road and the air brake system is working properly, the brakes are held away from the drum by:
Answer: air pressure
Q: When air pressure is lost or leaks off:
Answer: strong springs are released which apply the brakes automatically (these are known as springs brakes)
Q: A dual parking control valve means:
Answer: you can use air pressure from a separate tank to move your vehicle to a safe location
Q: If you have a dual air brake system and a low air pressure warning is activated, you:
Answer: stop immediately and get air system repaired
Q: The front brake limiting valve should be used:
Answer: never
Q: A COMBINATION vehicle air brake system, with engine OFF and brakes APPLIED, should not leak more than:
Answer: 4 psi in one minute
Q: With brakes APPLIED and engine OFF, air loss in a STRAIGHT truck or bus should not exceed:
Answer: 3 psi in one minute
Q: To check for play in the slack adjusters you must:
Answer: park vehicle on flat ground, chock wheels, release brakes and pull hard on the slack adjusters
Q: COMBIANTION vehicles with air brakes, engine OFF and brakes RELEASED, cannot lose more than:
Answer: 3 psi in a minute
Q: Stab braking means:
Answer: brake hard until wheels lock up then release until wheels begin to roll again
Q: A supply pressure gauge is:
Answer: required on all equipment with air brakes
Q: On long downhill grades, experts recommend using a low gear and only enough braking pressure to reduce vehicle speed to 5 mph below the “safe speed” for a hill, why?
Answer: 1. air usage is less when vehicle is in the proper low gear and brakes are applied only when needed to reduce to speed under the “safe speed”2. brake linings should not over heat if in the proper gear3. using this method allows you to maintain control of the vehicle
Q: When is “snubbing” the brakes on a long downgrade acceptable?
Answer: if brakes are properly adjusted and vehicle is in proper gear
Q: Air brakes take more time to work than hydraulic brakes due to:
Answer: brake lag
Q: You lose steering control when:
Answer: your steering tires lock up
Q: Effective braking distance is:
Answer: the distance your vehicle travels after brakes have been applied
Q: The most common type of foundation brake found on heavy vehicles is the:
Answer: “S” Cam Drum
Q: A supply pressure gauge shows:
Answer: air pressure in the air tanks
Q: When going down a long downgrade, the gear you should be in is:
Answer: a lower gear than the one used going up the grade
Q: The brake pedal in the air brake system:
Answer: controls the air pressure applied to put on the brakes
Q: Parking or emergency brakes of trucks and buses can be legally held by pressure.
Answer: spring
Q: The driver must be able to see a low air pressure warning which comes on before pressure in the service air tanks falls below psi.
Answer: 60
Q: All air brake equipment vehicles have:
Answer: a supply pressure gauge
Q: The braking power of the spring brakes:
Answer: depends on the service brakes being in adjustement
Q: The air loss rate for a STRAIGHT truck or bus with the engine OFF and the air brakes APPLIED should not be more than:
Answer: 3 psi in one minute
Q: True/False The Heavier a vehicle or the faster it is moving, the more heat the brakes have to absorb to stop it
Answer: True
Q: The purpose of engine retarders is to:
Answer: help slow the vehicle while driving and reduce brake wear
Q: If your vehicle has an alcohol evaporator, it is there to:
Answer: reduce the risk of ice in the air brake valves in cold weather
Q: The air supply pressure gauge shows the driver how much pressure:
Answer: is available in the air tanks
Q: Which brake system applies and releases the brakes when the driver uses the brake pedal?
Answer: the service brake system
Q: When using the parking brakes or emergency brakes, what type of pressure is being used?
Answer: spring pressure
Q: Three different systems are found on modern air brakes systems: service brakes, the parking brakes, and the:
Answer: emergency brakes
Q: Air loss in a SINGLE vehicle should not be more than with the engine OFF and the brakes ON
Answer: 3 psi in one minute
Q: The vehicle must have a warning device which comes on when air pressure in the service air tanks falls below:
Answer: 60 psi
Q: Air brake equipped vehicles must have:
Answer: an air pressure gauge, to show the pressure available for braking
Q: How do you check the free play in manual slack adjusters?
Answer: park on level ground, chock wheels, release the parking brakes and pull slack adjusters
Q: The most common type of foundation brake found on heavy commercial vehicles is:
Answer: “S” Cam Drum
Q: The air compressor governor controls:
Answer: when the compressor will pump air into the storage tanks
Q: The brake pedal:
Answer: Controls the air pressure applied to operate the brakes
Q: What will determine how effective the spring emergency braking or the parking brakes work?
Answer: depends on the adjustment of the service brakes
Q: When failure occurs in the service brake system, the system you need to stop the vehicle is the:
Answer: emergency brake system
Q: If your vehicle is equipped with an alcohol evaporator, every day during winter weather you should:
Answer: check and fill the alcohol level
Q: What turns on the electrical stop light switch in an air brake system?
Answer: air pressure
Q: What is okay to find on the air brake system?
Answer: Air
Q: If the air system should develop a leak, what will keep the air in the tanks?
Answer: the one-way check valve
Q: If your truck or bus has dual parking control valves, you can use pressure from a separate tank to:
Answer: release the emergency brakes to move a short distance
Q: In air brake equipped vehicles, you use the parking brakes when?
Answer: whenever you park the vehicle
Q: During normal operations, the parking and emergency brakes are usually held back by:
Answer: air pressure
Q: A COMBINATION vehicle air brake system cannot leak more than psi per minute with the engine OFF and the brakes RELEASED.
Answer: 3
Q: A STRAIGHT truck or bus air brake system cannot leak more than psi per minute with the engine OFF and the brakes RELEASED.
Answer: 2
Q: You must make a quick emergency stop. You should brake so you:
Answer: can stay in a straight line and maintain steering control
Q: Why should you not fan the brakes on and off during long downgrades?
Answer: the short time off the brakes does not allow brake cooling
Q: The correct way to use brakes on a long and/or steep downgrade?
Answer: use the braking effects of the engine and when the vehicle speed reaches the “safe” speed, apply brakes firmly until vehicle speed is reduced to approximately 5 mph below “safe” speed
Q: To use the “stab” braking technique during emergency braking, you:
Answer: brake hard with the pedal until the wheels lock, then get off them until the wheels begin rolling again.
Q: Modern air brakes systems combine three different systems. They are the service brakes, the parking brakes, and the
Answer: emergency brakes
Q: The air compressor governor controls:
Answer: when the compressor will pump air into the storage tanks
Q: A COMBINATION vehicle or bus air brakes system cannot leak more than per minute with the engine OFF and the brakes RELEASED.
Answer: 3 psi
Q: Oil and water that collects in the air tanks can make brakes fail. If you do not have automatic tank drains, when should you drain the air tanks?
Answer: every day
Q: Vehicles with air brakes must have:
Answer: an air pressure gauge, to show the pressure available for braking
Q: The driver must be able to see a warning that is given when air pressure in the service air tanks fails below:
Answer: 60 psi
Q: You should know that your brakes are fading when:
Answer: you have to push harder on the brake pedal to control your speed on a downgrade.
Q: To check the free play in manual slack adjusters you need to:
Answer: park on level ground, chock the wheels and release the parking brakes.
Q: Air braking takes more time than hydraulic braking because air brakes:
Answer: need to have air flow through the lines to work
Q: What makes total stopping distance longer for air brakes than hydraulic?
Answer: brake lag
Q: Experts do not recommend “fanning” (on-again off-again braking) for long downhill runs because?
Answer: the short time off the brakes does not allow the brakes to cool
Q: If the air compressor develops a leak, what keeps the air in the tanks?
Answer: the one-way check valve
Q: Why drain water from compressed air tanks?
Answer: water can freeze in cold weather and cause brake failure
Q: For long downhill grades, experts recommend light steady pedal pressure instead of on-again off-again braking. Why?
Answer: brake linings do not heat up as much with pressure
Q: Your vehicle has a dual air brake system. If a low air pressure warning comes on for the secondary system, you should:
Answer: stop, safely park, and continue only when the system is fixed
Q: During normal driving, spring brakes are usually held back by:
Answer: spring pressure
Q: In air brake vehicles, the parking brakes should be used:
Answer: whenever the vehicle is parked
Q: Why must air tanks be drained?
Answer: Compressed air usually has some water and some oil, which is bad for the air brake system. The water can freeze in cold weather and cause brake failure.
Q: What is a supply pressure gauge used for?
Answer: Shows how much pressure you are applying to the brakes
Q: All vehicles with air brakes must have a low air pressure warning system?
Answer: True
Q: What are spring brakes?
Answer: Brakes used to hold emergency brakes and parking brakes. Held by strong springs. If the air pressure drops the springs release and put on the brakes.
Q: Spring brakes will come on fully when the air pressure drops to a range of?
Answer: 20-45 psi
Q: The braking power of the spring brakes depends on
Answer: the brakes being in proper adjustment
Q: Front wheel brakes are good under all conditions.
Answer: True
Q: How do you know if your vehicle is equipped with antilock brakes?
Answer: Yellow ABS malfunction lamps on the instrument panel
Q: The brakes are what three different braking systems?
Answer: service brakes, parking brakes, and emergency brakes
Q: The service brakes system
Answer: applies and releases the brakes when you use the brake pedal during normal driving
Q: The parking brake system
Answer: applies and releases the parking brakes when you use the parking brake control
Q: The emergency brake system
Answer: uses parts of the service and parking brake systems to stop the vehicle in a brake system failure
Q: The air compressor
Answer: pumps air into the storage tanks
Q: Air compressor governor
Answer: controls when the air compressor will pump air into the air storage tanks
Q: The air tank “cut out” level will stop pumping air at:
Answer: around 125 psi
Q: When the “cut in” pressure fails to psi the governor allows the compressor to state pumping again
Answer: around 100 psi
Q: Air storage tanks will hold enough air:
Answer: to allow the brakes to be used several times, even if the compressor stops working
Q: Manually operated takes must be drained:
Answer: by you at the end of each day of driving
Q: Automatic air tanks are equipped with electric devices to help:
Answer: prevent freezing of the automatic drain in cold weather
Q: Check the alcohol evaporator container:
Answer: each day during cold weather and fill up as necessary
Q: The safety valve will open at psi
Answer: 150 psi
Q: The safety valve protects:
Answer: the tank and the rest of the system from too much pressure
Q: The safety valve is installed in:
Answer: the first tank the compressor pumps air into
Q: If the safety valve releases air:
Answer: something is wrong, have the fault fixed by a mechanic
Q: You put the brakes on by:
Answer: pushing down on the brake pedal
Q: Pressing and releasing the pedal unnecessarily:
Answer: can let air out faster than the compressor can replace it.
Q: If air pressure gets too low:
Answer: the brakes wont work
Q: Foundation brakes are:
Answer: used at each wheel
Q: Brake drums are located on:
Answer: each end of the vehicle’s axles
Q: Too much heat can make:
Answer: the brakes stop working
Q: What brakes are less common than “S” Cam Brakes
Answer: Wedge brakes & Disc brakes
Q: How many supply pressure gauges are on a dual air brake system?
Answer: a gauge for each half of the system or a single gauge with two needles
Q: A low pressure warning signal will come in before the air pressure in the tanks fall below:
Answer: 60 psi
Q: On large buses it is common for the low pressure warning device to come on at:
Answer: 80-85 psi
Q: The air brake system will warn drivers behind by:
Answer: an electric switch that works by air pressure called the stop light switch
Q: The parking brake is a:
Answer: diamond shaped, yellow push pull control knob
Q: Never push the brake pedal down when:
Answer: the springs brakes are on. The brakes could be damaged by the combined forces of the springs and the air pressure
Q: A modulating Control Valve will:
Answer: allow you to control the spring brakes if the service brakes fail.
Q: There is only enough air in the separate tank to:
Answer: allow you to move the vehicle a few times
Q: Vehicles with ABS have a yellow malfunction lamp to tell you:
Answer: if something is not working properly.
Q: ABS activates when:
Answer: your wheels are about to lock up
Q: ABS is an:
Answer: Addition to your normal brakes.
Q: ABS does not:
Answer: decrease or increase your normal braking capability
Q: True or False. ABS does not necessarily shorten your stopping distance, but does help you keep the vehicle under control during hard braking.
Answer: True
Q: What is a dual air brake system?
Answer: Has two separate air brake systems, which uses a single set of brake controls.
Q: Each System of a dual air brake system has its own air tanks, hoses, lines.
Answer: True
Q: The dual air brake system operates:
Answer: the regular brakes of the rear axle and the other system operates the brakes on the front axle.
Q: The first system is called the system
Answer: Primary
Q: The other system is called the system
Answer: Secondary
Q: Before driving a vehicle with a dual air system, allow time for the air compressor to build up to a minimum of psi pressure in both the primary and secondary systems
Answer: 100
Q: The warning light and buzzer should come on before the pressure drops below psi in either system
Answer: 60
Q: If the low pressure warning comes on while driving you should:
Answer: stop right away and safely park the vehicle
Q: If one air system is very low on pressure, either the front or rear brakes will not be operating fully. This means it will take you longer to stop and you should:
Answer: bring the vehicle to a safe stop and have the air brakes system fixed
Q: What are the slack adjusters?
Answer: Vehicles with too much slack can be very hard to stop
Q: How can you check the slack adjusters?
Answer: Park on level ground, chock the wheels to prevent the vehicle from moving. Release the parking brakes so you can move the adjusters.
Q: If the slack adjuster moves more than inch it probably needs adjustment.
Answer: about 1
Q: How can you test the low pressure warning signal?
Answer: Shut the engine off when you have enough air pressure so that the low pressure signal is not on. Turn the electrical power on and step on and off the brake pedal to reduce air tank pressure. The warning signal must come on before the pressure drops below 60 psi in the tank
Q: How can you check that the spring brakes come on automatically?
Answer: Continue to fan off the air pressure by stepping on and off the brake pedal to reduce tank pressure. The spring brakes should come on when pressure fails below 20-40 psi
Q: What are the maximum leakage rates?
Answer: When the engine is at operating rpms, the pressure should build from 85-100 psi within 45 seconds in dual air systems. In single air system pressure should build up from 50-90 psi within 3 minutes at an idle speed of 600-900 rpms.
Q: How do you test air leakage rates?
Answer: With a fully charged system typically 125 psi turn off the engine, release the parking brake, and time the air pressure drop. The loss rate should be less than 2 psi in one minute for single vehicles and less than 3 psi in one minute for combination vehicles. Then apply 90 psi or more with the brake pedal. After the initial drop, if the air pressure falls more than 3 psi in one minute for single vehicles or more than 4 psi in combination vehicles.
Q: How do you check air compressor governor cut-in and cut-out pressures?
Answer: Run the engine at an fast idle. The air governor should cut in at 100 psi and cut out at 125 psi. With the engine idling, step on and off the brake to reduce the air tank pressure. The pressure should cut-in at 100 psi
Q: How do you test the parking brake?
Answer: stop the vehicle, put the parking brake on, and gently pull against it in a low gear.
Q: How do you test the service brakes?
Answer: wait for normal air pressure, release the parking brake, move the vehicle forward slowly about 5mph and apply the brakes firmly using the brake pedal. Note any vehicle pulling to one side, unusual feel or delayed stopping action.
Q: Why should you be in the proper gear before starting down a hill?
Answer: Because the brakes on a long and/or steep downgrade is only a supplement to the braking effects the engine.
Q: What factors can cause the brakes to fade or fail?
Answer: from excessive heat caused by using them too much and not relying on the engine braking effect and if the brakes are not adjusted properly.
Q: The use of brakes on a long, steep downgrade is only a supplement to the braking effect of the engine. True or False
Answer: True
Q: If you are away from your vehicle only a short time, you do not need to use the parking brake. True or False
Answer: False
Q: How often should you drain air tanks?
Answer: at the end of each working day to remove moisture and oil. Otherwise the brakes could fail
Q: How do you brake when you drive a tractor-trailer Combination with ABS?
Answer: Brake as you always have. Use only the braking force necessary to stop safely and stay in control.
Q: You still have normal brake functions if your ABS is not working. True or False.
Answer: True
Q: ABS helps you avoid:
Answer: wheel lock up
Q: What is controlled braking?
Answer: apply brakes as hard as you can without locking up the wheels.
Q: What is stab braking?
Answer: apply your brakes all the way. Release the brakes when the wheels lock up. As soon as the wheels start rolling, apply the brakes fully again
Q: There is an delay when using air brakes
Answer: added. due to the time it takes for air to flow through the lines to the brakes.
Q: Perception Distance + Reaction Distance + Brake Lag Distance + Effective Braking Distance=
Answer: Total Stopping Distance
Q: On dry pavement at 55 mph on normal driving conditions, total stopping distance would be
Answer: over 450 feet
Q: If the low air pressure warning comes on you should:
Answer: stop and safely park your vehicle as soon as possible
Q: It will take a heavily loaded vehicle will take a to stop
Answer: longer distance
Q: A lightly loaded vehicle on slippery roads may when spring brakes come on
Answer: skid out of control