Mississippi CDL — Air Brakes Practice Test 5

1.A new driver says his truck has ABS, so he can follow closer because he will always stop shorter. What does the manual say?

ABS does not necessarily shorten stopping distance, but it helps keep the vehicle under control in hard brakingHe is right, since ABS cuts stopping distance in halfABS adds to normal braking power, so closer following is safeABS works only at highway speeds

2.You start a truck with a dual air brake system. The primary gauge reads 105 psi, but the secondary reads 80 psi. Are you ready to drive?

Yes, because one system above 100 psi is enoughNo; wait until the secondary system also reaches at least 100 psiYes, because both systems are above 55 psiNo; wait until both systems reach 150 psi

3.What is a downside of routinely adjusting automatic slack adjusters by hand?

It is likely to wear out the adjusters themselves earlyIt turns off the vehicle's ABSIt makes the brakes engage more slowlyThere is no downside; weekly adjustment is recommended

4.Which statement about automatic front-wheel limiting valves is true?

They are switched with a 'normal' and 'slippery' control in the cabThey raise front brake pressure on icy roadsThey let full air reach the front brakes only during very hard stops, and the driver cannot control themThey are found only on vehicles built before 1975

5.You watch your air gauge climb to about 125 psi and then hold steady. What is the most likely reason it stopped rising?

The safety valve opened to dump the extra airA leak is letting air out as fast as it comes inThe compressor broke down once the tanks were fullThe governor reached its cut-out point and stopped the compressor from pumping

6.Which list puts these air system pressure points in order from LOWEST to HIGHEST, using the typical values in the manual?

Low air warning, governor cut-in, governor cut-out, safety valve openingGovernor cut-in, low air warning, safety valve opening, governor cut-outLow air warning, governor cut-out, governor cut-in, safety valve openingSafety valve opening, governor cut-out, governor cut-in, low air warning

7.A parked truck slowly loses all its air overnight through a small leak. Why does its parking brake keep holding?

The governor locks the wheels when pressure dropsThe safety valve traps enough air to keep the brakes onIts spring brakes are applied by mechanical spring force, which does not depend on airThe ABS holds the brakes until the engine restarts

8.If your service brakes fail, how can a modulating control valve help you stop?

It releases the spring brakes so you can coast to a stopIt sends air from the trailer tanks to the tractor brakesIt lets you apply the spring brakes gradually, harder the farther you move the leverIt cuts front brake pressure in half

9.Your truck has an alcohol evaporator, and you keep it filled every cold day. Does that let you skip draining the air tanks?

Yes, because the alcohol absorbs all of the water and oilYes, but only during the summer monthsNo; the tanks still need daily draining to remove water and oil unless they drain automaticallyNo, but draining once a week is enough

10.Braking hard on a slick road in a vehicle without ABS, you lock the rear wheels but not the steering wheels. What is the main danger?

Losing all steering control at the frontNothing, since only steering-wheel lockup mattersA skid, a jackknife, or even a spinThe spring brakes applying on their own