Nebraska CDL — Air Brakes Practice Test 2

1.Which order matches how an s-cam brake applies after you press the pedal?

Air enters the slack adjuster, the s-cam moves out, the push rod twists, and the camshaft spreads the shoes against the drumThe camshaft twists, air enters the brake chamber, the shoes spread, and then the push rod moves outAir enters the brake chamber, the push rod moves out, the slack adjuster moves, the camshaft twists, and the s-cam spreads the shoes against the drumThe push rod moves out, air leaves the brake chamber, the s-cam pulls the shoes together, and the drum turns the camshaft

2.Air brakes are really three braking systems. Which pairing of a system with the way the driver works it matches the manual?

Service brakes – the parking brake control; emergency brakes – the brake pedalService brakes – the brake pedal; parking brakes – the parking brake controlParking brakes – the brake pedal; service brakes – the trailer hand valveEmergency brakes – the clutch pedal; parking brakes – the brake pedal

3.If a driver keeps overusing brakes that are already fading, where does the manual say this can end?

The spring brakes apply and stop the vehicle safelyThe vehicle can no longer be slowed or stoppedThe ABS takes over and restores full brakingThe governor cuts in and cools the drums

4.A truck's low air warning is a 'wig wag.' What does that device do when system pressure falls below 55 psi?

It sounds the horn in short burstsIt flashes the brake lights to warn traffic behindIt drops a mechanical arm into the driver's viewIt vents the tanks through the safety valve

5.The Step 7 check ends with a low-speed test of the service brakes. Why does the manual say this test is worth doing?

It warms the drums so the linings grip betterIt can reveal brake problems that would otherwise stay hidden until a real stop in trafficIt resets the automatic slack adjustersIt bleeds water out of the air tanks

6.At operating rpm, your dual air system with minimum-size tanks takes about 70 seconds to climb from 85 to 100 psi. How does that compare with the manual's standard?

Acceptable; the standard allows up to three minutesFaster than required; the standard is two minutesToo slow; the manual's standard is 45 seconds or lessAcceptable; buildup time is not part of the check

7.The manual contrasts air brakes with the hydraulic brakes on cars and light or medium trucks. How quickly does it say hydraulic brakes work once the pedal is pushed?

After about half a secondInstantlyAfter about one secondAfter about three seconds

8.Overheated brake drums expand. What does the manual say that does to the brake shoes and linings?

They seize against the drum and lock the wheelThey cool faster because more air can circulateThey must travel farther to reach the drum, and they press against it with less forceThey pull away from the s-cam and stop wearing

9.During the in-vehicle part of Nebraska's vehicle inspection test, you check the ABS indicator on the dashboard of a combination vehicle. What should the trailer's ABS light do?

The ABS light at the rear of the trailer on the driver's side should come on and then go offThe light on the passenger side should stay lit the whole timeIt should flash until the vehicle is moving faster than five mphNothing; the trailer's ABS light is checked only on the road test

10.A driver's CDL carries the L restriction. Under the definition Section 1 uses for that restriction, which vehicles is the driver barred from operating?

Only commercial vehicles whose brakes run entirely on airOnly tractor-trailers; straight trucks and buses are not coveredOnly combinations in which the trailer, but not the power unit, has air brakesCommercial vehicles with any type of air brakes, including systems that run only partly on air