Massachusetts CDL — Air Brakes: Handling Emergencies Practice Test

Question 1

How can brakes that are out of adjustment lead to a complete loss of braking on a long grade?

Accepted Answer

They quit carrying their share, so the remaining brakes take the extra heat, fade, and leave too little stopping power — Every brake has to carry part of the load; the ones out of adjustment quit early, dumping their share of the heat onto the rest, which then fade until too little braking is left to control the vehicle.

Answer

They lock their wheels first, which actually shortens the stop

Answer

They force the governor to cut the compressor out early

Answer

They raise the pressure at which the spring brakes apply

Question 2

On a tractor or straight truck, at roughly what pressure do the spring brakes come fully on by themselves?

Accepted Answer

20 to 45 psi — As air pressure falls into about the 20-to-45-psi range, the springs apply the brakes, but you should stop well before that happens.

Answer

55 to 75 psi

Answer

80 to 100 psi

Answer

100 to 125 psi

Question 3

You have just pushed through deep standing water and your brakes are soaked. How does the manual say to get them working again?

Accepted Answer

Keep the vehicle in a low gear and press the pedal gently as you drive so heat dries the brakes out — Staying in a low gear and riding the pedal gently builds enough friction heat to dry the soaked linings, which is why wet brakes should be dried out rather than simply parked on.

Answer

Pull and push the parking-brake knob repeatedly until the water clears

Answer

Open every tank drain valve and let the system blow itself dry

Answer

Coast in neutral at highway speed so airflow dries the linings

Question 4

Your tractor has ABS but the trailer behind it does not, and during a hard stop the trailer begins to swing out. What does the manual advise?

Accepted Answer

Back off the brake pedal, when it is safe to do so, until the trailer falls back into line — Watch the trailer whenever you brake hard, and when it starts to come around, ease pressure off the pedal if traffic and space allow so the unit can settle back into line.

Answer

Push harder on the pedal so the tractor pulls the trailer straight

Answer

Pull out the parking-brake control to set the spring brakes

Answer

Steer sharply toward the side the trailer is swinging to

Question 5

If one half of a dual air brake system loses most of its pressure while driving, what is the result?

Accepted Answer

Either the front or the rear brakes lose full power, so it takes longer to stop — With one system very low, either the front or rear brakes will not work fully, lengthening your stopping distance; stop safely and get it repaired.

Answer

The vehicle stops instantly with no warning

Answer

The other half shuts down as well

Answer

Nothing changes, since the halves are identical

Question 6

Why is it dangerous to keep rolling in a heavily loaded truck until the spring brakes grab on their own?

Accepted Answer

Because the springs work on only some of the axles, the loaded vehicle will travel a very long way before it stops — The springs do not act on every axle, so a loaded rig needs a very long distance to come to rest once they take over; stop while the foot brakes still have air.

Answer

The springs release again as soon as the vehicle slows below 20 mph

Answer

The engine will stall the moment the springs apply

Answer

The trailer brakes will lock and drag the tractor sideways

Question 7

After the start-up bulb check, the yellow ABS malfunction lamp stays lit. What does that tell you?

Accepted Answer

ABS may no longer be working at one or more of the wheels — A lamp that stays on after the bulb check, or comes on while driving, warns that one or more wheels may have lost ABS protection.

Answer

The ABS is working correctly

Answer

The parking brake is still set

Answer

The tanks are fully charged

Question 8

In the "controlled braking" method for an emergency stop, how do you use the brakes?

Accepted Answer

As firmly as possible short of locking the wheels, using only slight steering inputs — Controlled braking means squeezing the brakes hard but short of lockup, with small steering inputs; release if the wheels lock or you need to steer more.

Answer

As hard as possible, even if the wheels lock

Answer

Lightly, pumping the pedal quickly

Answer

Only with the parking-brake control

Question 9

What is a modulating control valve used for?

Accepted Answer

Applying the spring brakes gradually, so you can use them if the service brakes fail — A modulating valve lets you bring the spring brakes on smoothly by hand, useful as a backup if the service brakes quit.

Answer

Draining the air tanks automatically

Answer

Cutting air pressure to the front brakes

Answer

Warning you of low air pressure

Question 10

Which sequence describes the "stab braking" method?

Accepted Answer

Press the brakes fully, release when the wheels lock, then reapply fully once the wheels start rolling again — Stab braking is full application, release at lockup, then reapply once the wheels roll; allow up to a second for them to start turning before reapplying.

Answer

Pump the pedal gently while steering hard

Answer

Set the parking brake, then add the foot brake

Answer

Hold steady, light pressure all the way to a stop

Question 11

You always drive a rig whose antilock system is working on every axle. According to the manual, what does that change about an emergency stop?

Accepted Answer

You may press the brake pedal all the way down rather than metering it short of lockup — Full-axle working ABS is the single exception to normal emergency-stop practice: instead of controlled or stab braking, you are allowed to push the pedal all the way down and let the system prevent lockup.

Answer

You may follow other traffic more closely, since the stop will always be shorter

Answer

You should still pump the pedal in short stages the way stab braking calls for

Answer

Nothing changes; controlled braking is required no matter what equipment you have

Question 12

Some buses have dual parking control valves fed by a small separate air tank. What is that tank for?

Accepted Answer

Releasing the spring brakes a limited number of times so the vehicle can be moved during an emergency — The separate reservoir can release the spring brakes a limited number of times to move the vehicle in an emergency, so plan your moves carefully.

Answer

Keeping the alcohol evaporator topped off

Answer

Supplying extra pressure to the front brakes

Answer

Powering the ABS computer

Massachusetts CDL — Air Brakes: Handling Emergencies practice test

Study questions with answers

1. How can brakes that are out of adjustment lead to a complete loss of braking on a long grade?

2. On a tractor or straight truck, at roughly what pressure do the spring brakes come fully on by themselves?

3. You have just pushed through deep standing water and your brakes are soaked. How does the manual say to get them working again?

4. Your tractor has ABS but the trailer behind it does not, and during a hard stop the trailer begins to swing out. What does the manual advise?

5. If one half of a dual air brake system loses most of its pressure while driving, what is the result?

6. Why is it dangerous to keep rolling in a heavily loaded truck until the spring brakes grab on their own?

7. After the start-up bulb check, the yellow ABS malfunction lamp stays lit. What does that tell you?

8. In the "controlled braking" method for an emergency stop, how do you use the brakes?

9. What is a modulating control valve used for?

10. Which sequence describes the "stab braking" method?

11. You always drive a rig whose antilock system is working on every axle. According to the manual, what does that change about an emergency stop?

12. Some buses have dual parking control valves fed by a small separate air tank. What is that tank for?

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