Iowa CDL — Air Brakes Practice Test 6

11.To get credit for the air brake check on Iowa's pre-trip vehicle inspection test, what must you do?

Describe the steps aloud; no hands-on demonstration is neededPerform the steps silently while the examiner reads the gaugesPerform the check and also explain it correctlyHand the examiner a completed written checklist instead

12.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

13.Two drivers take the same long downgrade at the same speed. One is in a proper low gear and brakes only now and then. The other stays in a higher gear and rides the service brakes most of the way. Whose brakes are more likely to fade, and why?

The first driver's, because a low gear makes the brakes work harder on every applicationThe second driver's, because leaning on the service brakes without engine braking builds too much heatNeither one's, since air brakes are built to absorb any amount of heat a downgrade producesBoth equally, because brake fade depends only on how heavy the load is, not on technique

14.Four different rigs each lose 2.5 psi in one minute during their pre-trip air leakage checks, all with the engine off. Which rig should stay parked until the leak is found and fixed?

A tractor-trailer with the parking brake released and no brakes appliedA straight truck with the foot brake held fully downA straight truck with the parking brake released and no brakes appliedA tractor-trailer with the foot brake held fully down

15.You passed the air brakes knowledge test. In which skills-test vehicle would you avoid both the L and the Z air brake restrictions?

A truck with hydraulic brakesA truck whose brakes work fully on airA truck with air-over-hydraulic brakesAny of these, as long as you pass the skills test

16.During the engine-area fluid check on Iowa's inspection test, which fluid on the list applies only to vehicles with hydraulic brakes, not air brakes?

Brake fluidEngine oilCoolantPower steering fluid

17.What is the key difference between the controlled braking and stab braking methods for an emergency stop?

Controlled braking stays just short of locking the wheels; stab braking brakes fully and lets off whenever the wheels lockControlled braking relies on the parking brake; stab braking relies on the foot brakeControlled braking holds light, steady pressure; stab braking taps the pedal lightly and quicklyControlled braking is meant for hydraulic brakes; stab braking is only for vehicles with ABS

18.Your straight truck has ABS on all axles, but its yellow ABS lamp has stayed lit all day. A car stops suddenly ahead and you must brake hard. Which approach fits the manual?

Stand on the pedal and hold it, since full application is allowed on a truck with ABS on all axlesStop with the parking brake control alone, since the service brakes are tied to the failed ABSUse controlled or stab braking, since the regular brakes still work but the wheels can now lockPump the pedal lightly until the lamp goes out, and only then brake hard

19.You keep fanning off air after the low pressure warning test. On a straight truck with no trailer, what should pop out on its own once pressure falls to the manufacturer's setting?

The parking brake valve, setting the spring brakesBoth the tractor protection valve and the parking brake valveThe safety relief valve on the first air tankNothing; on single vehicles the spring brakes must be set by hand

20.In Iowa's air brake check, you have just finished the leakage test. What should you do about the engine before starting the low air warning test?

Restart it at a fast idle so the compressor keeps the gauges steadyRestart it, then shut it off again the moment the buzzer soundsTurn the key all the way off so the warning circuit can resetLeave it off and pump the brake pedal with the electrical power still on