Alaska CDL: Air Brakes Practice Test

Not quite. The answer is the air pressure may drop too low during driving.

The manufacturer's specifications should state how fast the air pressure should build up once the engine has reached normal operating speed. If the air pressure does not build up fast enough during your final air brake check, the air pressure may not replenish quickly enough during normal braking either. Don't drive the vehicle until the cause has been found and corrected.

Not quite. The answer is 10

A CMV has two foundation brakes per axle (one on each side). A typical 18-wheeler has five axles: the steering axle, the two tandem drive axles, and the two tandem semi-trailer axles. Therefore, there are 5 × 2 = 10 foundation brakes on the vehicle. Note: According to FMCSA, even a lift axle must have brakes when it is in contact with the roadway.

Not quite. The answer is The brakes could fail.

Water and oil from the compressor can collect at the bottoms of the air tanks. If the air tanks are not drained regularly, the water and oil can freeze or coagulate and cause brake failure.

Not quite. The answer is Never

Applying the spring brakes and the air brakes at the same time may put too much force on the brakes and can actually damage them.

Not quite. The answer is Drive normally until the ABS is repaired.

Losing the ABS function does not change the basic parts of your truck, so you will still have the same brakes that you have always had. Simply use them and get the ABS repaired as soon as possible.

Not quite. The answer is a Class A CDL without an air brakes restriction.

To legally pull a trailer whose gross vehicle weight rating (GCWR) exceeds 10,000 pounds, you'll have to obtain a Class A CDL. If you don't pass a knowledge test on air brakes, your CDL will include a restriction limiting you to driving only vehicles without air brakes.

Not quite. The answer is whenever you leave the vehicle unattended.

Because air pressure can leak when you're away from your vehicle, it should be set with the parking brake, to keep it from rolling. There is an exception to this rule: if the brakes are too hot or wet, use wheel chocks instead, to avoid brake damage or freezing.

Not quite. The answer is Leaky glad hand seals

Glad hands have rubber or urethane seals to form a tight connection and prevent air from escaping. The glad hands are constantly being connected and disconnected, so the seals tend to wear out over time. Leaky seals can cause loss of air pressure.

Not quite. The answer is It disables the spring brake.

If your vehicle's service brakes fail, the emergency (spring) brakes will activate and stop your vehicle. Then to tow your vehicle for repairs, it will be necessary to disable the spring brakes. A technician can manually compress or "cage" the spring in each spring brake chamber. Obviously, the vehicle will be undrivable at this point because it will have no working brakes at all.

Not quite. The answer is so you only have to apply the brakes just hard enough to feel a definite slowdown.

When starting down a downgrade, shift into a low gear and use engine braking to slow your vehicle. Apply the brakes just enough to keep your vehicle near your safe speed.

Not quite. The answer is (b) Spring brake priority

Instead of providing air pressure to both the service brakes and the spring brakes at the same time, trailer brake subsystems give priority to one or the other. Trailers with spring brake priority supply compressed air to the spring brakes (to release them) before the service tanks have filled. Trailers with service brake priority fill the service tanks before supplying air to the spring brakes. When coupling your tractor to a trailer with service brake priority, you must wait until the service tanks are full before you can release the trailer's parking brakes. Trailers more than 25 years old were more likely to implement service brake priority. Today's modern trailers are more likely to implement spring brake priority. Ask your employer or a qualified person whether your trailer uses spring brake priority or service brake priority.

Not quite. The answer is hazardous in direct exposure.

The compressed air that is used in air brake systems can be hazardous if you get near it when it is being exhausted from the vehicle. Compressed air leaving the vehicle travels at a very high speed and carries moisture, oil, dirt, and dust. To avoid exposing yourself to it, learn about all the places where the compressed air can be exhausted from your vehicle (such as the exhaust ports of brake valves).

Not quite. The answer is stop braking, turn quickly, and countersteer.

To recover from a drive-wheel braking skid, first stop braking. The rear wheels will unlock and roll again so there will be no more tendency to slide sideways. Then quickly steer your vehicle back on course. You may find that your vehicle will overshoot and keep on turning, possibly skidding in the opposite direction. Countersteer to counteract this. Note: This maneuver takes some practice. You should become proficient in it before you actually need to use it.

Not quite. The answer is emergency

The emergency brake system utilizes parts of the service brakes and the parking brakes in case your regular brakes fail and you need to come to a stop.

Not quite. The answer is 100 psi.

In a typical air brake system, pumping by the air compressor should start at about 100 psi and stop at about 125 psi. (Check the manufacturer's specifications for the actual figures.)

Not quite. The answer is Never

It used to be thought that applying the steering axle brakes on a slippery surface might cause a front-wheel skid. However, more recent tests have shown that front-wheel braking is good under all driving conditions. Front-wheel skids from braking are unlikely even on ice. Therefore, always have front-wheel braking available. If you're driving an old truck equipped with a front brake limiting valve, leave the control set at "normal" to have normal stopping power. The front-wheel brakes provide about 12% of the total stopping power of a loaded combination vehicle.

Not quite. The answer is Never

Never try to apply the brake pedal when the spring brakes are on. The combined force of the springs and the air pressure could damage the brakes. However, the brake systems on some (but not all) vehicles are designed to prevent this from happening.

Not quite. The answer is lets the air out of the brake chambers.

When you apply the parking brake control, air is released from the brake chambers, causing the springs to apply the brakes and hold your vehicle in place.

Not quite. The answer is the brakes when you depress the brake pedal during normal driving.

Air brakes are actually three braking systems in one: the emergency brake, the parking brake, and the service brake. As these terms suggest, when you depress the brake pedal in normal driving, it's the service brake system that applies the brakes.

Not quite. The answer is brake drum.

In North America, the most common type of foundation brake is the S-cam drum brake. The brake shoes and linings press against the inside of the brake drum, which causes friction to slow the wheel.