Wisconsin CDL — Air Brakes Practice Test 2

1.During the inspection you find that the low air pressure warning signal never comes on. Why does the manual treat that as a serious hazard?

The parking brakes could release on their own while you driveThe compressor would keep running and overheatAir could drain away unnoticed, so a single-circuit vehicle may brake suddenly and a dual system will take much longer to stopThe ABS would shut itself down above highway speed

2.According to the manual, what is the most common brake defect found during roadside inspections?

Cracked brake drumsFrozen drain valvesWorn air hosesBrakes that are out of adjustment

3.What effect does pushing the brake pedal down harder have?

It sends less air to the brakes to prevent lockupIt applies more air pressure to the brakesIt sets the parking brakesIt has no effect once the shoes touch the drums

4.On a modern air brake vehicle, the low air pressure warning must come on before tank pressure drops below what level?

60 psi100 psi125 psi20 psi

5.About how much distance does air brake lag add at 55 mph on dry pavement?

About 12 feetAbout 32 feetAbout 100 feetAbout 200 feet

6.On a newer air brake vehicle, how do you set the parking (spring) brakes?

Pull the yellow, diamond-shaped knob outwardPush the yellow, diamond-shaped knob inwardHold the brake pedal down for several secondsTurn the red, round knob to the left

7.In stab braking, why must you wait for the wheels to start rolling before reapplying the brakes?

So the tanks have time to refillSo the ABS can reset itselfReapplying before the wheels roll keeps the vehicle from straightening outSo the drums have time to cool

8.Why must the parking and emergency brakes be held on by mechanical force instead of air pressure?

Because springs react faster than air ever couldBecause air pressure can eventually leak away and let them offBecause federal rules ban air-held parking brakesBecause mechanical force burns less fuel

9.Your dual air system takes far too long to build pressure during the pre-trip check. What is the danger if you drive it anyway?

Tank pressure can fall too low while you are driving and force an emergency stopThe governor will begin cutting in far below its normal settingThe alcohol evaporator will flood the tanks with fluidThe ABS lamp will stay lit until the tanks are drained

10.Why is it risky to let the spring brakes set themselves instead of stopping under control first?

The spring brakes only work above 60 psiThey apply the front brakes twice as hardThey always overheat the drums instantlyA light load or slick road can skid, and a heavy load stops slowly since the springs miss some axles