New Hampshire CDL — Air Brakes Practice Test 3

11.Section 2 gives a minimum total stopping distance of 419 feet at 55 mph. The Air Brakes section gives a total of more than 450 feet at the same speed. What accounts for the difference?

A longer perception time for drivers of air-braked vehiclesThe extra weight of the air tanks and compressorBrake lag, which adds about 32 feet at 55 mph on dry pavementABS, which lengthens every stop

12.The Air Brakes section spreads its extra checks across the seven-step inspection. Which of these is done in the Step 7 final air brake check, not in the Step 5 walk-around?

Pulling on the slack adjustersLooking over brake drums and liningsChecking the air hoses at the brake chambersTiming the air leakage rate

13.You are testing the low pressure warning signal with the engine off and the electrical power on. Pumping the brake pedal, you watch the gauge fall to 50 psi before the warning finally comes on. What does that tell you?

The signal is not working as required; it must come on before pressure drops under 55 psiThe signal is fine; it only has to come on before 45 psiThe signal is fine; any warning above 20 psi is acceptableThe test is invalid because the engine has to be running

14.A straight truck's air leakage is checked both ways with the engine off. With the brakes released, the gauge falls 2.5 psi in one minute. With the foot brake held fully down, it also falls 2.5 psi in one minute. How do those results compare with the manual's limits for a single vehicle?

Within the limit on both testsToo much loss on both testsToo much loss with the brakes released, but within the limit with the foot brake appliedWithin the limit with the brakes released, but too much with the foot brake applied

15.In the manual's list of air brake parts, what are "foundation brakes"?

The spring brakes that hold a parked vehicleThe first air tank the compressor fillsThe half of a dual system that serves the rear axleThe brakes used at each wheel, most commonly S-cam drum brakes

16.Which gauge does the manual say all air-braked vehicles have, and which does it say is missing on some?

All have an application pressure gauge; the supply pressure gauge is not on every vehicleAll have both gaugesNeither gauge is on every vehicle; both are optionalAll have a supply pressure gauge; the application pressure gauge is not on every vehicle

17.One of the two air leakage tests in the Step 7 check times the pressure drop with your foot off the brake. Which of these is NOT part of setting it up?

Starting with a fully charged air systemHolding the foot brake fully appliedTurning the engine offReleasing the parking brake

18.Your truck has a manual-reset wig wag. With system pressure still at 45 psi, you push the arm up out of your line of sight. What does the manual say will happen?

The arm locks in place and the warning is canceledThe spring brakes releaseThe arm will not stay put until pressure is back above 55 psiThe compressor governor cuts out

19.The safety relief valve is usually set to open at a fixed pressure. Using the manual's usual numbers, about how far above the governor's cut-out level is that?

About 5 psiAbout 25 psiAbout 50 psiAbout 95 psi

20.Several faults described in the Air Brakes section are handed to a mechanic or a repair facility. Which of these tasks does the manual say you must do yourself?

Draining manually operated air tanks once each day of driving is overFixing the fault when the safety relief valve releases airCorrecting a brake whose automatic slack adjuster is out of adjustmentRebuilding a governor that will not cut in or cut out