Massachusetts CDL — Air Brakes Practice Test 8

11.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

12.You notice you must apply more and more pressure to hold the same speed. What does that usually mean, and what should you do?

The brakes are fading, so slow down and drop to a lower gearThe tanks are overfilled, so drain them at onceThe parking brakes are dragging, so pull the knob outThe governor has failed, so keep driving carefully

13.Why can you still apply the brakes a few times after the compressor quits?

The storage tanks keep a reserve of compressed airThe pedal mechanically clamps the shoes without airThe alcohol evaporator makes backup pressureThe wig wag pumps air when the compressor quits

14.At about what pressure does the governor "cut in" and let the compressor pump again?

About 150 psiAbout 125 psiAbout 55 psiAbout 100 psi

15.How do you test that the parking brake will hold?

Rev the engine to cut-out and listen for leaksDrain the tanks and see whether the vehicle rollsFirmly apply the foot brake at 5 mphSet the parking brake and gently try to pull forward in a low gear

16.Your tractor has ABS but the trailer behind it does not, and during a hard stop the trailer begins to swing out. What does the manual advise?

Push harder on the pedal so the tractor pulls the trailer straightBack off the brake pedal, when it is safe to do so, until the trailer falls back into linePull out the parking-brake control to set the spring brakesSteer sharply toward the side the trailer is swinging to

17.Air-brake trucks, buses, trailers, and converter dollies (other than truck tractors) built on or after which date must have antilock brakes?

January 1, 1994March 1, 1997March 1, 1998March 1, 1975

18.How is the air compressor usually driven on an air-brake vehicle?

By the exhaust gases spinning a turbineBy a stand-alone electric motorOnly by the drive shaft while coastingThe engine turns it through gears or a v-belt

19.Which sequence describes the "stab braking" method?

Press the brakes fully, release when the wheels lock, then reapply fully once the wheels start rolling againPump the pedal gently while steering hardSet the parking brake, then add the foot brakeHold steady, light pressure all the way to a stop

20.How do air-operated disc brakes differ from s-cam brakes?

They use a power screw rather than an s-cam to clamp the rotorThey need no slack adjusterThey apply the brakes with hydraulic fluid instead of airThey are the most common type on large trucks