Massachusetts CDL — Air Brakes Practice Test 7

11.An automatic front-wheel limiting valve reduces air to the front brakes except when what happens?

The brakes are applied very hard — about 55 psi or more of application pressureThe parking brake is setThe vehicle is going down a gradeThe ABS warning lamp is lit

12.When should you NOT rely on the parking brakes to hold the vehicle?

Any time the vehicle is on level groundWhen the brakes are very hot from a steep grade, or very wet in freezing temperaturesWhenever the tanks are fully chargedWhen the ABS lamp is off

13.How often should tanks with manually operated drain valves be emptied?

At the end of every day of drivingOnce a weekOnly when the low-air warning soundsEach time you stop for fuel

14.What most directly causes brake fade on a long downgrade?

Cold, damp brake liningsDraining the tanks too oftenSetting the parking brake while movingExcess heat from overusing the service brakes instead of relying on engine braking

15.Some buses have dual parking control valves fed by a small separate air tank. What is that tank for?

Keeping the alcohol evaporator topped offReleasing the spring brakes a limited number of times so the vehicle can be moved during an emergencySupplying extra pressure to the front brakesPowering the ABS computer

16.On a tractor or straight truck, at roughly what pressure do the spring brakes come fully on by themselves?

20 to 45 psi55 to 75 psi80 to 100 psi100 to 125 psi

17.The total stopping distance for an air-brake vehicle is made up of four parts. Which list is correct?

Perception, reaction, brake-lag, and braking distancesPerception, reaction, steering, and braking distancesReaction, brake-lag, skid, and braking distancesPerception, brake-lag, coasting, and braking distances

18.For an average driver on dry pavement in good conditions, the total stopping distance of an air-brake vehicle at 55 mph is roughly how far?

About 60 feetAbout 250 feetMore than 450 feetAbout 100 feet

19.On newer air-brake vehicles, what does the parking-brake control look like and how do you set it?

A round blue knob you push in to applyA yellow, diamond-shaped knob you pull out to apply and push in to releaseA red octagon you turn a quarter turnA foot pedal left of the service brake

20.How can brakes that are out of adjustment lead to a complete loss of braking on a long grade?

They quit carrying their share, so the remaining brakes take the extra heat, fade, and leave too little stopping powerThey lock their wheels first, which actually shortens the stopThey force the governor to cut the compressor out earlyThey raise the pressure at which the spring brakes apply