Air Brake Mock

#1. How often should you check brake chamber pushrod travel?

Monthly

Weekly

Daily

Only when the brakes seem to fade

According to the Canada National Safety Code, pushrod travel must be checked daily. Do it as part of your pre-trip inspection

#2. Which statement is true of spring brakes?

They are stronger than service brakes.

They are as strong as service brakes.

They can be used in lieu of service brakes.

They are not as strong as service brakes.

Spring brakes start to drag as pressure drops to 60 psi, and they release as pressure rises to 60 psi. Yet a full service brake application can be 100 psi. The coil spring in most spring parking brake chambers can exert a force of between 1,500 and 2,000 pounds. With a service brake application of 100 psi, a typical Type 30 brake chamber can produce a force of 30 × 100 = 3,000 pounds.

#3. Compared with the service tanks, how much moisture should the supply tank discharge?

The same amount of moisture

More moisture

Either less moisture or more moisture, depending on the manufacturer

Less moisture

The air that flows from the compressor to the supply tank usually contains some water vapour, much of which condenses into liquid water inside the tank. This is why the supply tank is often called the “wet” tank. The air that travels from the supply tank to the service tanks is likely to be drier.

#4. Compounding the air brakes can

damage the slack adjusters.

damage the foundation brakes.

damage the brake chambers.

do all of the above.

Compounding the air brakes means fully applying both the service brakes and the spring brakes (such as when setting the parking brakes) at the same time. Each service brake can exert a force of up to 3,000 pounds, and each spring brake can exert up to 2,000 pounds, for a total of up to 5,000 pounds. This large force can damage slack adjusters, S-cams, brake chamber mounting bolts, brake shoe rollers, brake shoes, and brake drums.

#5. Polarized gladhands on a tractor

can be incorrectly connected to polarized trailer couplers.

cannot be connected to trailers built before 1975.

can be incorrectly connected to non-polarized trailer couplers.

cannot be incorrectly connected to non-polarized trailer couplers.

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.

#6. Which of the following can affect pushrod stroke?

Normal brake wear

Brake fade

All of the above

The kind of brake chamber

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.

#7. Which of the following statements are true about a foot control valve?

(a) It is tolerant of small air leaks downstream.

(b) It needs reservoir pressure to control it to within 10 psi.

(c) It allows you to select any brake application pressure that you need.

Both (a) and (c) are true.

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.

#8. Your vehicle passes the tug test of the parking brakes if

the wheels only turn a half revolution.

the truck moves 1.5 metres or less.

the front wheels are blocked.

the vehicle moves only slightly back and forth.

To perform a tug test, first make sure that the engine is on, the transmission is in a low gear, and the parking brakes are set. Then try to pull forward. The parking brakes should prevent the vehicle from doing more than just slightly rocking back and forth. If you see the wheels actually roll, it means the vehicle has failed the tug test. This counts as a major defect. The vehicle cannot be legally driven on the road until this defect is repaired.

#9. The spring brakes will start to apply when the air pressure falls below

60 psi.

66 psi.

50 psi.

55 psi.

If air pressure falls below 414 kPa (60 psi), the spring brakes will begin to apply automatically.

#10. The air-loss rate test can be performed only when

both the spring and service brakes are released.

the spring brakes are released and the service brakes are applied.

both the spring and service brakes are applied.

the spring brakes are applied and the service brakes are released.

To perform the air-loss rate test, first secure the vehicle and release the spring brakes. Next, ensure that air pressure is within its normal operating range. Now fully apply and hold the brake pedal to keep sending compressed air to the service brakes. Watch your air pressure gauges and see what happens to the service tank air pressures.

#11. In an air braking system, which of the following is not commonly part of a disc brake?

Rotor

Caliper

Pad

Spider

In an air braking system, the three most common types of foundation brakes are S-cam drum brakes, disc brakes, and wedge brakes. Components of S-cam drum brakes include include brake drums, brake shoes and linings, camshafts, pushrods, cam support brackets, spiders, rollers, return springs, dust shields and backing plates, slack adjusters and brake chambers. In an S-cam drum brake, the brake shoes are mounted to the brake spider. Components of disc air brakes include rotors, calipers, brake pads, slack adjusters and brake chambers.

#12. You must make heavy brake applications as part of your pre-trip inspection. Why should you release the spring brakes first?

To prevent the brakes from applying fully

To obtain a true gauge reading

To avoid compounding the pressures

To permit the brakes to apply fully

Compounding the air brakes means fully applying both the service brakes and the spring brakes (such as when setting the parking brakes) at the same time. Each service brake can exert a force of up to 3,000 pounds, and each spring brake can exert up to 2,000 pounds, for a total of up to 5,000 pounds. This large force can damage slack adjusters, S-cams, brake chamber mounting bolts, brake shoe rollers, brake shoes, and brake drums.

#13. When inspecting the air brake chambers, what should you look for?

Mismatched slack adjuster effective lengths

All of the above

Cracks

Non-manufactured holes

Slack adjusters act as levers that increase the force of the air brake chambers. Their effective length is critical. Most slack adjusters are designed with two or three holes for attachment of the pushrod. Attaching the slack adjuster using a different hole changes the slack adjuster’s effective length. Make sure that the effective lengths of the slack adjusters on both sides of each axle (especially the steering axle) are the same. Also look for cracks and holes that are indicators of damage (not normal vent holes).

#14. An air line shows signs of wear from rubbing, but there are no leaks because the inner tube is still in good shape. What should you do?

Have the air line replaced after your day's work is complete.

Have the air line replaced before you drive the vehicle.

Drive slowly and monitor the condition of the air line.

Note this in the logbook and continue.

Air line chafing is a common roadside violation. If you’re pulled over for a roadside inspection, you can be cited for brake line chafing. If the chafing continues, the inner tube may be damaged eventually as well.

#15. Assuming good traction and constant vehicle speed, if you double your vehicle's weight, your vehicle's braking distance will be

Doubled.

Tripled.

Quadrupled.

Eight times as long.

The kinetic energy of a moving object is directly proportional to the object’s weight. A vehicle that is twice as heavy has twice the kinetic energy. Brakes use friction to convert the kinetic energy of a moving vehicle into heat. Thus, if you double your vehicle’s weight, it will take twice as long for your brakes to stop your vehicle.

#16. What is the "cut-in" level?

The pressure level that triggers the governor to turn off the air compressor

The pressure level that triggers the governor to turn on the air compressor

The maximum speed of your vehicle that the air brakes can stop safely

The safest pressure level at which you can shut off the engine

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.

#17. How should you test the spring brakes?

Release the spring brakes and try to pull forward a bit.

Apply the service brakes and and try to pull forward a bit.

Apply the spring brakes and try to pull forward a bit.

Release the service brakes and try to pull forward a bit.

To test the spring brakes, first remove any wheel chocks. Set the parking (spring) brakes by pulling out the yellow dashboard knob. Then gently apply engine power in low gear. The parking brakes should keep your vehicle from moving.

#18. What happens to the foot valve when you press down on the brake pedal?

The foot valve signals the compressor to turn on.

The foot valve closes.

The foot valve opens.

The foot valve signals the compressor to turn off.

The brake pedal is attached to a valve underneath it, which is called the brake valve or foot valve. When you press the brake pedal, the foot valve opens, allowing air from the service tanks to flow to the brake chambers. The harder you press the brake pedal, the more the valve opens, sending more air to the brake chambers and causing braking force to increase.

#19. It is important to keep compressed air as dry as possible because

moisture may freeze and cause brake failure.

moisture may cause air brakes to rust.

humid air is associated with low air pressure.

humid air may cause incorrect readings on the pressure gauges.

Water and oil from the compressor can collect at the bottoms of the air tanks. If the air tanks are not drained regularly, the water can freeze and cause brake failure. Some air brake systems include an alcohol evaporator to prevent ice from forming in the air brake system. (Alcohol has a lower freezing point than water.)

#20. The braking system converts the kinetic energy of the moving vehicle into

Heat.

Moisture.

Compressed air.

Oil.

Brakes use friction to convert the kinetic energy of a moving vehicle into heat. The heat must be dissipated by the brakes before it impairs braking effectiveness (brake fade) or damages the brakes.

#21. You're parking a tractor-trailer whose trailer does not have spring brakes, so you set the trailer service brakes. If the trailer air tank drains,

The trailer brakes will release.

Nothing will happen.

Both the tractor brakes and the trailer brakes will release.

The tractor brakes will release.

In a vehicle or trailer that is equipped with air brakes, the service brakes work by air pressure. The problem with using service brakes as parking brakes is that over time, the air pressure may bleed down and may cause the brakes to release. Most trailers equipped with air brakes also have spring brakes, which should be used as parking brakes. If your trailer doesn’t have spring brakes, apply the trailer service brakes and block (chock) the wheels in case the trailer service brakes release.

#22. To test the trailer's service brakes independently of the tractor's service brakes, what should you do?

Pull out the yellow dashboard knob.

Pull out the red dashboard knob.

Apply the spike brake.

Press the brake pedal.

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. Pressing the brake pedal activates the service brakes on the entire vehicle. The red dashboard knob controls the spring brakes on the trailer only. The yellow dashboard knob controls the spring brakes on the entire vehicle.

#23. Where are a vehicle's air tanks located?

Inside the engine compartment

Inside the cab

Under or around the frame

Above or around the frame

Air from the compressor is stored in air tanks. Located under or around the frame of the vehicle, these tanks are usually made of steel and shaped like cylinders with domed ends.

#24. How should you test your vehicle's low air pressure warning signal?

Pump the brakes while your ignition is off.

Repeatedly press and release the brake pedal to lower the air pressure to 207 kPa (30 psi).

Manually let the air out of your brakes and see if the signal comes on.

Repeatedly press and release the brake pedal to lower the air pressure to 414 kPa (60 psi).

Start the test with the pressure above 621 kPa (90 psi) and the ignition on. Then repeatedly press and release the brake pedal. In most vehicles, the low air pressure warning signal should come on when the pressure falls below 414 kPa (60 psi). If the warning device fails to activate at 414 kPa (60 psi), the low air pressure warning device is defective. You should never need to get down to 207 kPa (30 psi).

#25. Before beginning the air-loss tests of the air braking system, make sure that the air pressure approximately equals

100 psi.

The cut-out pressure.

The cut-in pressure.

120 psi.

As described in the British Columbia Air Brake Manual, the first air brake test is a test of the governor’s operation. After the test is performed successfully, rebuild air pressure back to the maximum (at which point the governor should cut out). Then proceed with the air-loss tests. This question is based on the Pre-Trip Procedures sections in the BC Air Brake Manual.