Alaska CDL — Air Brakes Practice Test 9

1.Your truck's wig wag is the manual reset type. Its arm has dropped, and you try to put it back while pressure is still under 55 psi. What happens?

It locks out of view and cancels the warning until the next time you start the engineIt releases the spring brakesIt makes the compressor cut in earlyIt will not stay out of view until system pressure is above 55 psi

2.You hook up to an older trailer built before ABS was required, and you can't tell whether it has ABS. What does the manual suggest?

Look underneath for the electronic control unit and wheel speed sensor wiresAssume it has ABS if the glad hands and air lines are color coded red and bluePump the brakes ten times with the engine off and listen for a click at each wheelCheck whether the air tanks have automatic drains

3.On an older ABS system, how long might the malfunction lamp stay lit after start-up as part of normal operation?

Until the engine reaches operating temperatureUntil the first hard brake applicationFor the first 30 minutes of drivingUntil you are traveling faster than five mph

4.How does an air brake system switch on the brake lights so that drivers behind you are warned?

An electric switch worked by air pressure turns them on when you apply the brakesThe driver flips a dash switch before each stopThe governor lights them whenever the compressor cuts in, whether or not you are brakingThe wig wag arm closes the circuit when it drops

5.On a long grade, overheated brake drums expand. What does the manual say this does to the brake shoes and linings?

They reach the drum sooner and grip harderThey are unaffected, since only the drum changes size while the shoes stay in the same placeThey have to travel farther to reach the drum and press on it with less forceThey lock against the drum and cannot release

6.You press the brake pedal on a truck with s-cam brakes. Which sequence matches the manual?

Air enters the brake chamber, the push rod moves out, the slack adjuster twists the camshaft, and the s-cam presses the shoes against the drumThe s-cam turns first, which pumps air into the brake chamber, pulls the push rod in, and loosens the slack adjuster against the drumThe slack adjuster releases air to the drum, the drum squeezes inward, and the shoes stay stillA spring pushes the shoes outward, and air pressure then pulls them back from the drum

7.Some automatic air tank drains can be had with electric heating devices. What are the heaters for?

Warming the compressed air so the brakes apply harder in winterBoiling the alcohol out of the evaporatorKeeping the automatic drain from freezing in cold weatherDrying the brake linings after rain

8.For single air systems, found on vehicles from before 1975, what air pressure buildup does the manual give as a typical requirement?

From 85 psi to 100 psi in 45 seconds with the engine at operating rpm, the same as a dual systemFrom 50 psi to 90 psi in 3 minutes or less with the engine idling at 600 to 900 rpmFrom 0 psi to 125 psi in one minute at fast idleFrom 20 psi to 45 psi in ten seconds with the engine off

9.Besides brake fade, the manual lists other things that can make you need more application pressure than usual. Which of these is NOT on its list?

Brakes that are out of adjustmentAir leaksMechanical problemsA burned-out warning light

10.Total stopping distance for an air-braked vehicle is made up of four parts. Which of these is NOT one of them?

Perception distanceBrake lag distanceBraking distanceCut-in distance