Iowa CDL — Air Brakes Practice Test 4

1.You usually drive a medium truck with hydraulic brakes, but today you're in an air-braked truck at the same speed. Even if you react just as quickly, how should this change the room you leave ahead?

Leave the same room, because air brakes work the instant you touch the pedalLeave less room, because air brakes stop a truck faster than hydraulic brakesLeave more room, because air brakes need half a second or more to start working after you press the pedalLeave more room only on wet roads, because brake lag disappears on dry pavement

2.During the air leakage part of Iowa's air brake check, you press the foot brake all the way down. When does the one-minute timing start?

The moment your foot first touches the pedalAfter the gauge settles from the first drop caused by applying the brakesOnce the low air warning buzzer soundsAs soon as you restart the engine

3.Parked at a fuel stop with the engine running, you hear the safety relief valve on the first air tank let air out. How should you treat this?

As a fault in the system that a mechanic needs to repairAs normal venting each time the governor stops the compressorAs the automatic drain clearing water and oil from the tankAs the alcohol evaporator purging ice out of the valves

4.While you're driving, a mechanical arm suddenly swings down into your view. What has happened?

The governor has cut out the compressor at about 125 psiThe ABS has sensed a wheel that is about to lockThe safety relief valve has opened at about 150 psiThe air pressure in the system has dropped below 55 psi

5.Automatic slack adjusters are meant to keep brakes in adjustment, yet one of yours is past its legal pushrod stroke limit. Which explanation does the manual NOT offer for that?

A mechanical problem inside the adjusterA problem with the foundation brake parts connected to itAn adjuster that was installed incorrectlyAir tanks that were not drained at the end of the day

6.On Iowa's inspection test, you check the brake lines and hoses at the steering axle. According to the manual, what may a loss of air pressure in those lines cause?

The safety relief valve openingThe wheels locking upThe governor cutting out earlyFaster pressure buildup when the engine restarts

7.While checking the engine area on Iowa's inspection test, you hear air hissing. Why does the manual treat an air leak there as important?

It shows the safety relief valve is working normallyIt matters only if a puddle forms under the engineIt means the alcohol evaporator needs refillingIt can point to a failing part, such as the air compressor, that is hard to inspect directly

8.On Iowa's inspection test, you check that the power unit's parking brake holds a combination vehicle. How should the trailer brakes be set during that check?

Released, so only the power unit's parking brake is holdingApplied, so the trailer helps hold the rigReleased, with your foot holding the service brake downIt does not matter, as long as the vehicle does not move

9.Your truck has automatic air tank drains and an alcohol evaporator. During a cold snap, which daily task does the manual still give you?

Check the alcohol container and top it up as neededOpen each drain valve by hand at the end of the dayRun the engine at a fast idle until the safety valve opensBleed the tanks down to 55 psi to push out moisture

10.On the walk-around, the slack adjusters on two trucks each move about two inches at the push rod when you pull on them. One truck has manual slack adjusters and the other has automatic ones. What does the manual point you toward?

Adjust both by hand, since any slack adjuster moving more than about an inch simply needs taking upAdjust the manual one or have it adjusted, and get the automatic one to a repair shop soon because its stroke signals a mechanical faultLeave both alone, since slack adjusters only need attention if the service brake test pulls to one sideSend the manual one to a repair shop, and hand-adjust the automatic one back within its legal limit before leaving