Maine CDL — Air Brakes: Safe Driving Practices Practice Test

Question 1

With the engine off, you fully apply the foot brake on a tractor-trailer and hold it for one minute. The air gauge falls 3.5 psi in that minute. How does that compare with the manual's standard?

Accepted Answer

It is acceptable, because a combination vehicle may lose up to four psi in a minute with the brakes applied — With the foot brake held down, the limit is three psi per minute for a single vehicle and four psi per minute for a combination. A 3.5 psi drop on a tractor-trailer is inside that limit.

Answer

It is too much, because any loss over two psi fails this test

Answer

It is too much, because any loss over three psi fails for every vehicle

Answer

It is acceptable only if the engine is restarted during the minute

Question 2

Two different kinds of gauge on an air-braked vehicle report air pressure. Which pairing of gauge and reading is correct?

Accepted Answer

Supply pressure gauge: the pressure held in the air tanks. Application pressure gauge: the pressure you are putting on the brakes — Supply pressure gauges are connected to the air tanks and show how much pressure they hold. The application pressure gauge, which not every vehicle has, shows how much air pressure is going to the brakes.

Answer

Supply pressure gauge: the pressure you are putting on the brakes. Application pressure gauge: the pressure held in the air tanks

Answer

Supply pressure gauge: tire inflation. Application pressure gauge: the pressure held in the air tanks

Answer

Both gauges show the same tank pressure, one for each axle

Question 3

Some pre-1975 vehicles are fitted with a front brake limiting valve, and many newer vehicles have an automatic front wheel limiting valve. What separates the two from the driver's seat?

Accepted Answer

The older type has a control in the cab, while the automatic type cannot be controlled by the driver — The older valve comes with a cab control, usually marked 'normal' and 'slippery,' that the driver sets. Automatic limiting valves cut back front brake air on their own, except in very hard applications of 55 psi or more, and the driver has no way to control them.

Answer

The automatic type has a cab control, while the older type works on its own

Answer

Both have a cab control marked 'normal' and 'slippery'

Answer

Neither one changes the air going to the front brakes

Question 4

On Maine's vehicle inspection test, you inspect the brake lines and hoses at an axle. Which of these is NOT one of the things the manual has you inspect?

Accepted Answer

That each line is at least one inch across — The manual has you confirm the hoses or lines can supply the brakes without leaking, check for any that are cracked, frayed or worn, and make sure the couplings and fittings are secure. It gives no minimum size for the lines.

Answer

That the hoses or lines are not leaking

Answer

That no hose or line is cracked, worn or frayed

Answer

That couplings and fittings are secure

Question 5

The manual's check of the governor's cut-out and cut-in points uses the engine at two different speeds. Which pairing is correct?

Accepted Answer

Fast idle while pressure builds to cut-out; idling while you pump the brake to bring pressure down to cut-in — With the engine at a fast idle, you watch for the gauge to stop rising, which shows the governor has cut the compressor out. Then, with the engine idling, you work the brake pedal until the compressor cuts back in and the pressure starts to climb.

Answer

Idling while pressure builds to cut-out; fast idle while you pump the brake to bring pressure down to cut-in

Answer

Fast idle for both parts of the check

Answer

Engine off for both parts of the check, with the key on

Question 6

Several parts of the Step 7 final air brake check have you pump the brake pedal so that tank pressure comes down. Which of these checks does NOT work that way?

Accepted Answer

Checking the rate of air pressure buildup — You pump the pedal to lower tank pressure for the cut-in check, the low pressure warning test, and the spring brake check. The buildup check goes the other way: with the engine at operating rpm, you time how fast the pressure rises.

Answer

Finding the governor's cut-in pressure

Answer

Testing the low pressure warning signal

Answer

Checking that the spring brakes apply on their own

Question 7

Most heavy-duty vehicles have a dual air brake system instead of a single one. What reason does the manual give?

Accepted Answer

Safety — According to the manual, safety is why most heavy-duty vehicles are built with dual air brake systems. The two systems are separate, each with its own tanks, hoses and lines, while sharing one set of brake controls.

Answer

Lower fuel use

Answer

Quieter brake operation

Answer

Faster air pressure buildup

Question 8

Where does the manual say the brake drums are found on a vehicle?

Accepted Answer

At both ends of the vehicle's axles — Brake drums sit at each end of the axles, and the wheels bolt to them. The braking mechanism itself is inside the drum.

Answer

At the middle of each axle, beside the differential

Answer

Inside the air storage tanks

Answer

Only on the rear axles, behind the brake chambers

Question 9

Which of these parts is NOT in the chain that applies an s-cam brake when you press the pedal?

Accepted Answer

The power screw — In an s-cam brake, air enters the brake chamber and drives the push rod out, which moves the slack adjuster and twists the brake camshaft to turn the s-cam. A power screw belongs to air disc brakes, where it takes the s-cam's place.

Answer

The brake chamber and its push rod

Answer

The slack adjuster

Answer

The brake camshaft

Question 10

A new driver believes the governor sets how hard the brakes apply when the pedal is pressed. What does the governor actually do?

Accepted Answer

It controls when the compressor pumps air into the storage tanks — The governor manages the compressor. It stops the pumping at the cut-out level, around 125 psi, and lets it start again at the cut-in level, around 100 psi.

Answer

It decides how much air reaches the front brakes on slick roads

Answer

It opens to vent the tanks when pressure gets dangerously high

Answer

It turns on the brake lights when the pedal goes down

Question 11

One part of the final air brake check confirms that the spring brakes apply on their own. As you keep fanning off air on a tractor-trailer, which controls should pop out when pressure falls to the manufacturer's specification?

Accepted Answer

Both the tractor protection valve and the parking brake valve — On a tractor-trailer, the tractor protection valve and the parking brake valve should both close, or pop out, somewhere from 20 to 45 psi. On other combinations and on single vehicles, it is the parking brake valve that closes. This puts the spring brakes on.

Answer

Only the parking brake valve

Answer

Only the tractor protection valve

Answer

Neither, because the valves on a combination never pop out

Question 12

On Maine's inspection test, you check the air and electric line connections on a combination vehicle. What must you do to receive credit for that item?

Accepted Answer

Check the connections at the power unit and at the trailer — A note in the combination vehicle part of the inspection test says the connections have to be inspected at both ends, on the power unit and on the trailer, for the item to count.

Answer

Check the connections at the power unit only

Answer

Disconnect each line and reconnect it for the examiner

Answer

Start the engine and build pressure to governor cut-out first

Maine CDL — Air Brakes: Safe Driving Practices practice test

Study questions with answers

1. With the engine off, you fully apply the foot brake on a tractor-trailer and hold it for one minute. The air gauge falls 3.5 psi in that minute. How does that compare with the manual's standard?

2. Two different kinds of gauge on an air-braked vehicle report air pressure. Which pairing of gauge and reading is correct?

3. Some pre-1975 vehicles are fitted with a front brake limiting valve, and many newer vehicles have an automatic front wheel limiting valve. What separates the two from the driver's seat?

4. On Maine's vehicle inspection test, you inspect the brake lines and hoses at an axle. Which of these is NOT one of the things the manual has you inspect?

5. The manual's check of the governor's cut-out and cut-in points uses the engine at two different speeds. Which pairing is correct?

6. Several parts of the Step 7 final air brake check have you pump the brake pedal so that tank pressure comes down. Which of these checks does NOT work that way?

7. Most heavy-duty vehicles have a dual air brake system instead of a single one. What reason does the manual give?

8. Where does the manual say the brake drums are found on a vehicle?

9. Which of these parts is NOT in the chain that applies an s-cam brake when you press the pedal?

10. A new driver believes the governor sets how hard the brakes apply when the pedal is pressed. What does the governor actually do?

11. One part of the final air brake check confirms that the spring brakes apply on their own. As you keep fanning off air on a tractor-trailer, which controls should pop out when pressure falls to the manufacturer's specification?

12. On Maine's inspection test, you check the air and electric line connections on a combination vehicle. What must you do to receive credit for that item?

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