Mississippi CDL — Air Brakes Practice Test 9

1.In stop-and-go traffic you keep pressing and releasing the brake pedal far more than you need to. What could this lead to?

The governor cutting out early and overfilling the tanksThe spring brakes releasing on their ownBrake lag dropping to zeroAir leaving the system faster than the compressor can replace it, until the brakes no longer work

2.Which statement about automatic air tank drains is accurate?

They push out water and oil on their own, and some can also be drained by handThey still have to be opened by hand at the end of every dayThey cannot be fitted with heaters for cold weatherThey remove water but leave the compressor oil in the tank

3.On a long downgrade in the right low gear, your 'safe' speed is 50 mph. You just braked down to about 45 mph and let off. When do you brake again?

Right away, to get down to 40 mphWhen your speed climbs back up to 50 mphOnly if you reach 60 mphNot again; hold 45 mph using the engine alone

4.Besides making the drums expand, what does excessive heat do to the brake linings?

It causes chemical changes that lower their frictionIt makes them grip harder until they lockIt turns them into a better heat shieldIt has no effect on the linings themselves

5.Total stopping distance for a vehicle with air brakes is made up of four distances. Which of these is NOT one of them?

Perception distanceBrake lag distanceBraking distanceCoasting distance

6.You park after driving through slush, the brakes are soaked, and the temperature is below freezing. Why might setting the parking brakes be a mistake?

They will release by themselves as they dryThey could freeze so the vehicle cannot moveWet parking brakes drain the air tanksThe ABS lamp will stay on

7.At operating rpm, your dual air truck with standard-size tanks takes about two minutes to climb from 85 to 100 psi. What does that tell you?

That is normal for any dual air systemThe governor needs to cut out soonerPressure is building too slowly, so do not drive until it is fixedYou should drive gently and it will catch up

8.Some pre-1975 trucks carry a front brake limiting valve worked from the cab. What was it meant to do, and what is the catch?

It was meant to reduce front-wheel skids on slick roads, but it actually reduces stopping powerIt was meant to cool the front brakes, but it wears out the liningsIt was meant to add front braking on ice, but it locks the rear wheelsIt was meant to replace ABS, but it works only above 55 mph

9.On some older air-braked vehicles, the visible low air warning is not tied to 55 psi. What is it based on instead?

The safety valve's opening pressureThe governor's cut-in pressureA fixed 80 to 85 psiOne half of the compressor governor's cut-out pressure

10.Your truck has air tanks larger than the minimum size, and building from 85 to 100 psi takes a bit longer than 45 seconds. What does the manual say?

A longer buildup can still be safe; check the manufacturer's specificationsIt is always a defect that must be repaired before drivingLarger tanks should fill faster than 45 secondsRemove the extra tanks to meet the time limit