Kansas CDL — Air Brakes Practice Test 3

1.Why does the manual tell you to check brake adjustment often, rather than only at the pre-trip inspection?

Automatic slack adjusters only work during the first few miles of a tripAdjustment can change only when the air tanks are drainedBrakes can slip out of adjustment fast, particularly when they are hotEach time the governor cuts in, it loosens the slack adjusters

2.Your straight truck's air system is fully charged at about 125 psi. For the first leakage check, you turn off the engine, push in the parking brake knob, and simply time the pressure drop. What loss rate is acceptable?

Less than 2 psi in one minuteLess than 3 psi in one minuteLess than 5 psi in one minuteAny rate, provided the low air warning stays off

3.Which chain of events correctly describes how an s-cam brake applies after you press the pedal?

The slack adjuster pumps air into the chamber, and the drum turns the s-cam to pull the shoes inwardThe s-cam drives a power screw that squeezes a rotor between two padsAir presses the shoes straight against the drum, and the s-cam then locks them thereAir enters the brake chamber, the push rod moves the slack adjuster, the camshaft turns the s-cam, and the shoes are forced out against the drum

4.During your final air brake check, the gauge climbs past 125 psi and keeps rising until air starts blowing off at the first tank at around 150 psi. What does this point to?

Normal operation; every system vents at 150 psiThe governor isn't cutting out the compressor, and the safety valve is releasing the excess; have it repairedThe air tanks need to be drained before drivingThe low air warning is set too high

5.On an air-braked vehicle, during which step of the seven-step inspection do you check the slack adjusters, brake drums, linings, and brake chamber hoses?

Step 2, the engine compartment checksStep 5, the walk-around inspectionStep 7, the final air brake checkStep 1, the vehicle overview

6.During a pre-trip inspection you suspect a truck's brakes have far too much slack. What is the main danger if that goes unfixed?

The vehicle can be very hard to stopThe ABS lamp will stay onThe compressor will run nonstopThe spring brakes will refuse to release

7.In an emergency stop, when does the manual say an ABS-equipped vehicle's brakes may be pushed all the way down?

Whenever the tractor has ABS, even if the trailer does notWhenever the pavement is dry and the vehicle is loadedWhen the straight truck or combination you drive always has working ABS on all of its axlesOnly once the ABS malfunction lamp has come on during the trip

8.On a long downgrade, a couple of your truck's brakes are out of adjustment while the rest are properly adjusted. How does this lead to trouble?

The adjusted brakes lock up, which sets off the spring brakes on the drive axlesThe poorly adjusted brakes overheat first and turn on the ABS malfunction lampThe air compressor falls behind, so the tanks empty before the bottom of the gradeThe badly adjusted brakes stop pulling their weight, so the others overheat and fade

9.Which of these would NOT cause the spring brakes on an air-braked truck to apply?

Pulling out the parking brake control knobA leak that drains all the air from the systemPressing hard on the service brake pedalAir pressure falling into the 20 to 45 psi range

10.Your truck has a modulating control valve on the dash for applying the spring brakes. How do you use it when you park?

Push the lever to the end of its travel and lock it there with its locking deviceSet the lever halfway so the spring brakes stay partly releasedLeave the lever alone and hold the truck with the service brake pedalPull the lever and let it spring back so the brakes release