Texas CDL — Air Brakes Practice Test 4

1.Why is it a bad habit to press and release the brake pedal over and over when you don't need to?

It wears out the stop light switch and burns out the brake lightsIt overheats the drums even when you are moving slowlyIt confuses the antilock computer and shuts off ABSIt can bleed off air faster than the compressor replaces it

2.The braking power of the spring brakes depends on what?

The service brakes being properly adjustedThe setting of the front brake limiting valveHow much fuel is in the tanksThe governor cut-out pressure

3.While driving down a long hill, you notice you must push the pedal harder and harder to get the reading shown on the application pressure gauge to hold the same speed. What does this increasing application pressure tell you?

The brakes are fading and you should slow down and use a lower gearThe governor cut-out setting is too highThe air compressor is overcharging the tanksThe stop light switch has failed

4.At roughly what air pressure range will tractor and straight truck spring brakes come fully on by themselves?

55 to 75 psi85 to 100 psi100 to 125 psi20 to 45 psi

5.Your tractor has a front brake limiting valve with a "normal" and a "slippery" setting. What did the slippery setting do on these older systems, and how should the control be set?

It doubled front brake pressure; use slippery only in rainIt reduced front brake air pressure by half; leave the valve in normalIt disconnected the rear brakes; use slippery on ice onlyIt engaged the spring brakes; never move it while driving

6.The low air pressure warning comes on while you are driving. What is the correct response?

Downshift and continue to the next truck stopPump the brake pedal to rebuild pressureStop and safely park as soon as possibleTurn the governor to a higher cut-out setting

7.Most heavy-duty vehicles built today use dual air brake systems. What does that mean?

There are two brake pedals, one for each axle groupAir brakes are backed up by a hydraulic master cylinderTwo separate air systems share a single set of brake controlsEach wheel has its own compressor and tank

8.You are braking hard in a tractor-trailer where only the tractor has antilock brakes. What should you watch for?

The trailer swinging out; ease off the brakes if it does and you safely canThe tractor's steering wheels locking, since tractor ABS cannot prevent thatThe ABS lamp flashing, which is your signal to pump the pedal rapidlyNothing extra, because the tractor's ABS keeps the trailer from skidding too

9.Why does an air-braked vehicle need a greater following distance than a car traveling the same speed?

Brake lag adds stopping distance that hydraulic brakes do not haveAir brakes only work below 45 mphTrucks have better tires, so they can follow closer if neededThe governor limits how hard the pedal can be pressed

10.During the final air brake check, how do you make sure the parking brake is strong enough to keep the vehicle still?

Set it while rolling at about 5 mph and see whether the vehicle comes to a stopStop, apply the parking brake, and ease the vehicle against it in a low gearFan the brake pedal until the parking brake knob pops outCheck that the parking brake knob is yellow and diamond-shaped