Massachusetts CDL — Air Brakes Practice Test 3

1.What does an alcohol evaporator do in an air brake system?

Raises tank pressure past the governor cut-outFilters oil out of the compressed airLowers the chance of ice forming in brake valves during cold weatherEnds the need to drain the tanks in winter

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

Keep the vehicle in a low gear and press the pedal gently as you drive so heat dries the brakes outPull and push the parking-brake knob repeatedly until the water clearsOpen every tank drain valve and let the system blow itself dryCoast in neutral at highway speed so airflow dries the linings

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

The ABS is working correctlyThe parking brake is still setABS may no longer be working at one or more of the wheelsThe tanks are fully charged

4.The total stopping distance for an air-brake vehicle is made up of four parts. Which list is correct?

Perception, reaction, brake-lag, and braking distancesPerception, reaction, steering, and braking distancesReaction, brake-lag, skid, and braking distancesPerception, brake-lag, coasting, and braking distances

5.At about what pressure does the governor "cut in" and let the compressor pump again?

About 150 psiAbout 125 psiAbout 55 psiAbout 100 psi

6.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?

You may follow other traffic more closely, since the stop will always be shorterYou should still pump the pedal in short stages the way stab braking calls forNothing changes; controlled braking is required no matter what equipment you haveYou may press the brake pedal all the way down rather than metering it short of lockup

7.What is the role of the service brake system?

It applies and releases the brakes with the pedal during ordinary drivingIt holds the vehicle still after you park and walk awayIt stops the vehicle only when an air line rupturesIt feeds compressed air to the tires

8.Water and compressor oil settle in the bottom of the air tanks. Why does that make draining important?

The added weight noticeably hurts fuel economyOil will clog the alcohol evaporator within an hourTrapped water can turn to ice in winter and cause the brakes to failFull tanks stop the governor from cutting out

9.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?

Push harder on the pedal so the tractor pulls the trailer straightBack off the brake pedal, when it is safe to do so, until the trailer falls back into linePull out the parking-brake control to set the spring brakesSteer sharply toward the side the trailer is swinging to

10.On an air-brake vehicle, what is "brake lag"?

The time the compressor needs to refill the tanksThe short delay before the air reaches and works the brakes after you press the pedalThe distance traveled while you decide to brakeThe pause before the spring brakes release