Air Brake Mock
#1. Which of the following can affect pushrod stroke?
Pushrod stroke adjustment limits vary depending on the size and type of the air brake chamber. As the brakes wear, brake pushrod stroke increases. If drum brakes overheat, the drum may expand away from the brake shoes. You will have to press the brake pedal farther (increasing pushrod stroke) to achieve the same amount of braking force that you did before. This is known as brake fade.
#2. When brakes become overheated, they also become
Overheating of the brakes can lead to a loss of braking effectiveness, known as brake fade. Your vehicle may take longer to stop. If brake fade continues to worsen, your service brakes may stop working completely. Brake fade is a particular problem for drum brakes, because excessive heat causes the brake drums to expand away from the brake linings.
#3. Which of these vehicles is most likely to be equipped with air brakes?
Air brakes are favored for large commercial vehicles because (a) they can produce large braking forces (typically thousands of pounds of braking force at each wheel); and (b) unlike hydraulic fluid, compressed air can be rapidly and automatically replenished in the event of a slow leak.
#4. Why is it important for you to check the slack adjusters?
If your brakes aren’t properly adjusted, they may not be able to stop your vehicle safely, possibly resulting in a serious accident. Federal and provincial laws require that you check manual and automatic slack adjusters daily, during the pre-trip inspection. You may be fined as much as $2,000 for driving a vehicle with defective brakes. This includes excessive brake chamber pushrod stroke.
#5. The effectiveness of the spring brakes for emergencies or parking
The effectiveness of a vehicle’s spring brakes depends on the condition of the brakes and proper brake adjustment. If the brakes are out of adjustment (for example, the pushrod stroke is excessive), neither the service brakes nor the spring brakes may work properly.
#6. What is the maximum available pushrod stroke of a typical Type 30 brake chamber?
The most common type of air brake chamber used on trucks and trailers is the Type 30. These chambers have a maximum available pushrod stroke of 2½ inches (65 mm). A long-stroke Type 30 brake chamber is designated Type 30LS and has a maximum available stroke of 3 inches (76 mm)
#7. When can you adjust automatic slack adjusters?
Once properly installed, automatic slack adjusters shouldn’t need manual adjustment. If an automatic slack adjuster strokes beyond the maximum allowed, this usually indicates that there are other brake problems that need to be repaired by a qualified brake service mechanic. If you are not so qualified, then don’t attempt to adjust an automatic slack adjuster except in an emergency in which your brakes have failed on the road
#8. How can you tell if you have cross-connected the supply line and the service (control) line on a tractor-trailer with air brakes?
If you cross-connect the air lines, supply air will be sent to the service (control) line instead of the trailer air reservoirs. Reservoir air will not be available to release the trailer spring brakes (parking brakes). And when you press the brake pedal, service air won’t flow to the trailer brake chambers or relay valves, so the service brakes won’t work either.
#9. To obtain an air brake endorsement in British Columbia, you must do which of the following?
To obtain an on-highway air brake endorsement in British Columbia, you must meet the following requirements: 1. Complete an air brake course (see the ICBC website for types of courses and their providers). 2. Pass a knowledge test on air brakes. 3. Pass an air brake pre-trip inspection test. 4. Pay the required fees. A road test in a vehicle equipped with air brakes is NOT required. Note: There are two types of air brake courses. If you successfully complete a driver-certification air brake course instead of the standard air brake course, you won’t be required to pass the air brake pre-trip inspection test. [“Air Brake Endorsements,” ICBC, https://www.icbc.com/driver-licensing/types-licences/Pages/Air-brake-endorsements.aspx]
#10. You can usually make a normal stop by applying no more than
Even though truck air brake system pressures are 100 psi (690 kPa) and above, much lower air application pressure, usually less than 20 psi (138 kPa), is used to make normal stops.
#11. When draining the air tanks, you observe excessive oil coming out of the supply tank. Which of the following is most likely to be faulty?
Most modern air compressors are lubricated with the engine’s own oil supply. It’s normal for an air compressor to pass a trace amount of this engine oil. However, if the air dryer or supply tank has been contaminated with excessive oil, it could mean that the compressor is faulty and should be replaced.
#12. What is the purpose of the hand valve?
The trailer hand valve control (also known as a spike, a trolley valve, or a Johnson bar) controls the service brakes only on the trailer, not the tractor. You can use it to test the trailer service brakes independently of the tractor service brakes, such as after coupling your tractor to a trailer and during your pre-trip inspection of the combination vehicle.
#13. When are you required to complete a pre-hill inspection?
British Columbia has many mountainous roads. You must perform a brake pre-hill inspection (brake check) wherever a sign is posted requiring you to do so before a steep hill ahead. (You may be fined for failing to stop to conduct a brake pre-hill inspection.) It’s also wise to perform a pre-hill inspection before every long or steep downgrade.
#14. Polarized gladhands on a tractor
To prevent cross-connection of the supply and service lines, polarized gladhands and polarized trailer couplers are now available. The supply gladhands and couplers are shaped slightly differently from the service gladhands and couplers, making cross-connection impossible. However, polarized gladhands can still be connected to universal (non-polarized) trailer couplers, so cross-connection in this situation is still possible.
#15. What does caging a brake chamber do?
If your vehicle’s service brakes fail, the emergency (spring) brakes will activate and stop your vehicle. Then to tow your vehicle for repairs, it will be necessary to disable the spring brakes. A technician can manually compress or “cage” the spring in each spring brake chamber. Obviously the vehicle will be undrivable at this point because it will have no working brakes at all.
#16. As air pressure builds during your pre-trip inspection of the air brakes, the low air pressure warning device should deactivate at
The low air pressure warning device must activate when pressure falls to 60 psi (414 kPa) and deactivate when pressure rises to the same level – 60 psi (414 kPa). However, it activates at even higher pressures in some vehicles.
#17. When you use the free stroke (pry bar) method, the pushrod should not move more than
To measure pushrod stroke with the free stroke (pry bar) method, use a pry bar to pull the pushrod out of the brake chamber. It should only move ½ – ¾ inch (13 mm – 19 mm). If the pushrod moves more than that, the brake needs adjustment.
#18. If drum brakes overheat, the vehicle's stopping distance will increase. What is the reason for this?
In a drum brake, a brake shoe contacts the inner surface of the brake drum, and the resulting friction slows the wheel. If the drum brake overheats, the brake drum will expand away from the brake shoe to the point that braking effectiveness is reduced. This is known as brake fade.
#19. To inspect an air brake system, you should wear
The compressed air that is used in air brake systems can be hazardous if you get near it when it is being exhausted from the vehicle. Compressed air leaving the vehicle travels at a very high speed and carries moisture, oil, dirt and dust. Plus there is always the chance of an accident in procedures that require you to release the brakes and crawl underneath your vehicle to inspect various items. While you’re inspecting the air brakes, wear a bump cap or hard hat, safety glasses, a visible safety vest, and steel toe boots.
#20. Which of the following statements are true about a foot control valve?
The foot control valve is a foot-controlled pressure regulator. It allows you to select any brake application pressure that you need for either gentle or emergency stops. The foot valve can maintain the application pressure that you’ve chosen, even if there are small leaks downstream from the foot valve.
#21. What is the purpose of a relay valve?
Relay valves are used to reduce the lag time, both when the brakes are applied and when they’re released. Relay valves are remote-controlled air valves that respond to a control signal from the foot valve. These valves are located near the brake chambers that they operate, and they receive a large volume of air from the service reservoirs. When the brake pedal is pressed, the control signal directs the relay valve to send air to the brake chambers. When the brake pedal is released, the air from the brake chambers is exhausted from a port in the nearby relay valve instead of having to flow back to the foot valve to be exhausted there. Only the air in the control line must flow back to the foot valve.
#22. Which of these can contaminate a brake system's air lines?
The air produced by the compressor and delivered to the supply tank usually contains some water vapour and a small amount of oil and carbon particles. This is usually normal and not a cause for concern as long as you drain the air tanks of this material daily.
#23. After you've connected your tractor to a trailer, you should test the trailer service brakes by applying
After connecting your tractor to the trailer, test the action of the trailer service brakes by applying the hand control valve. This valve applies only the trailer service brakes, not the tractor service brakes. For this reason, the trailer hand valve should not be used for normal braking once your vehicle is on the road.
#24. To “tug test” the trailer service brakes after you couple your tractor to the trailer, you should apply
After coupling your tractor to the trailer, use the hand control valve to test the action of the trailer service brakes. This valve applies only the trailer service brakes, not the tractor service brakes. First, release the entire vehicle’s parking brakes. Next, slowly pull away and use the hand control valve to apply the trailer brakes to check their operation.
#25. What is the "cut-in" level?
A typical air compressor can produce air pressures of up to 500 psi (over 3,000 kPa), far higher than required for safe operation of the brake system. Therefore, an air compressor governor is employed to keep tank pressures within a relatively narrow range. When tank pressure rises to the “cut-out” level the governor prevents the compressor from pumping more air into the tanks. When the tank pressure falls to the “cut-in” level, the governor allows the compressor to pump air into the tanks again.