Pennsylvania CDL — Air Brakes Practice Test 2

1.In an s-cam brake, what happens when you press the brake pedal?

A wedge is driven straight between the two brake shoesA power screw clamps a rotor between two padsAir enters the chamber, and the rod turns the s-cam so the shoes press against the drumHydraulic fluid pushes a piston against a disc

2.On large buses, at roughly what pressure do the low-pressure warning devices commonly activate?

20 to 30 psiRight at 55 psiAbout 80 to 85 psi120 to 140 psi

3.Which sequence correctly describes stab braking?

Press lightly and hold steady pressure until you stopSet the parking brake and release it over and overBrake fully and never release until you are stoppedBrake hard, release when the wheels lock, then reapply fully as they begin rolling

4.How does an air brake system light up the brake lights for the drivers behind you?

An air-pressure-operated electric switch turns them on as you brakeThe governor sends a signal back to the taillightsA contact at each wheel is closed by the slack adjusterThe wig wag completes the lighting circuit

5.What is true about front-wheel braking on a commercial vehicle?

Front brakes should be disabled on wet roadsFront-wheel braking helps in all conditions and rarely causes skids, even on iceFront brakes are only useful on dry pavementFront-wheel braking sharply raises the chance of a skid

6.As air is used and tank pressure falls, at about what level does the governor let the compressor start pumping again?

About 150 psiAbout 55 psiAbout 100 psiAbout 20 psi

7.On newer air brake vehicles, how do you apply the parking (spring) brakes?

Push in the round blue knobPull out the yellow, diamond-shaped control knobPress the brake pedal all the way to the floorCenter the modulating lever

8.If the ABS warning lamp shows the system has failed, what is true about your brakes?

You have lost all braking abilityOnly the parking brake still worksYour regular brakes still work; get the ABS repaired soonThe spring brakes will apply on their own

9.On dry pavement at 55 mph, about how much distance does air brake lag add?

About 60 feetAbout 100 feetAbout 12 feetRoughly 32 feet

10.Which statement about ABS is correct?

It prevents wheel lockup in hard braking but may not shorten the stopping distanceIt always shortens your stopping distanceIt replaces your normal service brakesIt runs continuously the whole time the vehicle is moving