Pennsylvania CDL — Air Brakes Practice Test 8

1.What is a 'wig wag'?

A lever that gradually applies the spring brakesA mechanical arm that drops into view when air pressure falls below 55 psiA valve that limits pressure to the front brakesA gauge needle that shows applied pressure

2.After you release the brakes during stab braking, about how long can it take for the wheels to start rolling again?

Up to five secondsAbout ten secondsThere is no delay at allAs much as one second

3.On some buses, what is the separate air tank tied to the parking-brake system used for?

Supplying extra air to the trailer brakesKeeping the alcohol evaporator topped offReleasing the spring brakes briefly so the vehicle can be movedPowering the ABS computer

4.Which sequence correctly describes stab braking?

Press lightly and hold steady pressure until you stopSet the parking brake and release it over and overBrake fully and never release until you are stoppedBrake hard, release when the wheels lock, then reapply fully as they begin rolling

5.Older vehicles had a front brake limiting valve with a 'normal/slippery' control. What did the 'slippery' setting do?

It doubled the pressure to the front brakesIt shut off the rear brakes completelyIt reduced the front-brake air pressure by halfIt engaged the spring brakes

6.What is the purpose of a modulating control valve?

It drains the air tanks automaticallyIt lets you apply the spring brakes gradually if the service brakes quitIt limits air pressure to the front wheelsIt recharges the secondary system

7.Where is the ABS malfunction lamp located on a trailer?

On the rear bumper at the centerOn the instrument panel inside the cabOn the left side, at a front or rear cornerBehind the tractor's grille

8.What is 'brake lag' on an air brake system?

The brief delay while air moves through the lines before the brakes take holdThe time it takes the driver to spot a hazardThe distance traveled after the wheels lock upThe pause before the compressor cuts in

9.What causes brake fade?

Water freezing inside the brake chambersAir pressure climbing above the governor cutoutThe alcohol evaporator running dryToo much heat from overuse, which reduces lining friction and expands the drums

10.As air is used and tank pressure falls, at about what level does the governor let the compressor start pumping again?

About 150 psiAbout 55 psiAbout 100 psiAbout 20 psi