Nebraska CDL — Air Brakes: Safe Driving Practices Practice Test

Question 1

On a vehicle with drum brakes, what does the manual say the wheels are bolted to?

Accepted Answer

The brake drums — Brake drums sit at each end of the axles, and the wheels bolt onto them. The braking mechanism is housed inside the drum, where the shoes and linings press against the drum's inner surface to create the friction that slows the vehicle.

Answer

The slack adjusters

Answer

The brake chambers

Answer

The brake camshafts

Question 2

In the first part of Nebraska's Air Brake Check you build air pressure up to governor cutoff. What else does the Nebraska Specifics page expect you to do at that point?

Accepted Answer

Identify the cutoff pressure for the vehicle you are testing in — For the air gauge and governor cutoff check, the driver chocks the wheels when needed, gets the vehicle started, confirms the air gauge works, builds pressure to governor cutoff (roughly 120 to 140 psi) and names the cutoff pressure for the vehicle being used.

Answer

Shut the engine off and drain every air tank

Answer

Pump the pedal until the low air warning comes on

Answer

Set the parking brake and pull against it in a low gear

Question 3

Automatic front wheel limiting valves, found on many vehicles, hold back air to the front brakes. At what point do they stop doing so?

Accepted Answer

When the brakes are applied very hard, at 55 psi or more of application pressure — Automatic front wheel limiting valves cut the air going to the front brakes during ordinary braking and stop limiting only on a very hard application, 55 psi or more. Unlike the older cab-controlled valve, the driver has no control over them.

Answer

When tank pressure drops below 55 psi

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When the driver moves the cab control to 'normal'

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When road speed drops below five mph

Question 4

What does the manual say about how many air storage tanks a vehicle has and how big they are?

Accepted Answer

Both the number and the size differ from one vehicle to another — Air storage tanks hold the compressed air, and the manual says both how many there are and how large they are differ among vehicles. They store enough for several brake applications even if the compressor quits.

Answer

Every air-braked vehicle has exactly two tanks of equal size

Answer

There is one tank per axle, sized by axle weight

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Federal rules fix the same number and size for every vehicle

Question 5

Front brake limiting valves were fitted to some vehicles made before 1975. What were they supposed to accomplish?

Accepted Answer

Make the front wheels less likely to skid on slippery surfaces — The valves were meant to cut the chance of a front wheel skid on slick roads by halving front brake pressure in the 'slippery' setting. The manual points out that they actually reduce stopping power and that tests show front wheel skids from braking are unlikely even on ice, so the control belongs in 'normal.'

Answer

Shorten the stopping distance on dry pavement

Answer

Keep the front brake linings from wearing out

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Hold air in the front brake chambers while parked

Question 6

Is an application pressure gauge found on every vehicle with air brakes?

Accepted Answer

No; the manual notes that not all vehicles have one — The application pressure gauge tells the driver how much air pressure is going to the brakes, and the manual notes that not every vehicle has one. Supply pressure gauges, by contrast, are on all air-braked vehicles.

Answer

Yes; it is required wherever a supply pressure gauge is required

Answer

Yes, but only on vehicles built since 1994

Answer

No; it is found only on trailers

Question 7

The manual calls air brakes a good, safe way to stop large and heavy vehicles. What two conditions does it attach to that statement?

Accepted Answer

They have to be kept in good repair and used correctly — The opening of Section 5 explains that compressed air is what works the brakes, and that the system is a safe way to stop big vehicles provided it is well maintained and properly used.

Answer

The vehicle has to be empty and the road dry

Answer

The driver has to use stab braking and stay under 55 mph

Answer

The system has to be single-circuit and drained every hour

Question 8

During the walk-around you look at the air hoses that run to the brake chambers. What are you looking for?

Accepted Answer

Hoses that are cut or worn from rubbing — The walk-around covers drums or discs, linings and hoses. For the air hoses at the brake chambers, the check is that they have not been cut or worn through by rubbing.

Answer

Hoses that are a different color from the others

Answer

Hoses longer than half the width of the drum

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Hoses that feel warm after a short drive

Question 9

Section 2 lists what to check regularly while you are on a trip. Which instrument does it name specifically for vehicles with air brakes?

Accepted Answer

The air pressure gauge — Among the instruments to watch during a trip, Section 2 lists the air pressure gauge for drivers who have air brakes, along with temperature gauges, pressure gauges and the ammeter or voltmeter. Any sign of trouble you notice on the road should be checked out.

Answer

The tachometer

Answer

The odometer

Answer

The fuel gauge

Question 10

A truck tractor with air brakes was built in 1995, before ABS was required on tractors. What does the manual say about whether it might have ABS?

Accepted Answer

It might; many commercial vehicles made before the required dates were given ABS voluntarily — ABS became mandatory on air-braked truck tractors built on or after March 1, 1997, but many vehicles made earlier were fitted with it by choice. The manual points drivers to the certification label, which shows when the vehicle was manufactured.

Answer

It cannot; ABS did not exist for air brakes before 1997

Answer

It must; ABS has been required on every tractor since 1975

Answer

It might, but only if it pulls a trailer built after 1998

Question 11

During the Step 7 air leakage test your pressure falls faster than the manual allows. What does the manual tell you to do?

Accepted Answer

Find the air leaks and get them fixed before you drive — When the air loss rate is higher than the manual's limits, the driver is to look for leaks and have them repaired before driving. Skipping that risks losing the brakes on the road.

Answer

Drive, but stop to rebuild pressure every hour

Answer

Drain the tanks and repeat the test until it passes

Answer

Raise the governor cut-out pressure to make up the loss

Question 12

A new mechanic makes four statements about the air compressor. Which one does NOT agree with the manual?

Accepted Answer

It runs off its own electric motor and has no connection to the engine — The engine drives the compressor, by gears or by a v-belt, and the compressor pumps air into the storage tanks. It can be air cooled or use the engine's cooling system, and it is lubricated either by engine oil or by its own oil supply, which you check before driving.

Answer

It pumps air into the storage tanks

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It may be cooled by air or by the engine's cooling system

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It may carry a separate oil supply or share the engine's oil

Nebraska CDL — Air Brakes: Safe Driving Practices practice test

Study questions with answers

1. On a vehicle with drum brakes, what does the manual say the wheels are bolted to?

2. In the first part of Nebraska's Air Brake Check you build air pressure up to governor cutoff. What else does the Nebraska Specifics page expect you to do at that point?

3. Automatic front wheel limiting valves, found on many vehicles, hold back air to the front brakes. At what point do they stop doing so?

4. What does the manual say about how many air storage tanks a vehicle has and how big they are?

5. Front brake limiting valves were fitted to some vehicles made before 1975. What were they supposed to accomplish?

6. Is an application pressure gauge found on every vehicle with air brakes?

7. The manual calls air brakes a good, safe way to stop large and heavy vehicles. What two conditions does it attach to that statement?

8. During the walk-around you look at the air hoses that run to the brake chambers. What are you looking for?

9. Section 2 lists what to check regularly while you are on a trip. Which instrument does it name specifically for vehicles with air brakes?

10. A truck tractor with air brakes was built in 1995, before ABS was required on tractors. What does the manual say about whether it might have ABS?

11. During the Step 7 air leakage test your pressure falls faster than the manual allows. What does the manual tell you to do?

12. A new mechanic makes four statements about the air compressor. Which one does NOT agree with the manual?

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