New York CDL: Air Brakes Practice Test

Not quite. The answer is All of the above are correct.

On both tractor-trailers and single vehicles, to test whether the spring brakes will come on automatically, use the same method you use for testing the low air pressure warning signal: Step on and off the brake pedal, this time until you reach an even lower psi reading and the parking brake valve closes or pops out.

Not quite. The answer is 32 feet

55 mph = 81 feet per second. Air brake lag typically lasts about 0.4 seconds. Therefore, the lag distance equals 81 feet per second × 0.4 seconds = 32 feet.

Not quite. The answer is a supply pressure gauge.

A supply pressure gauge is connected to a service tank (or possibly to both service tanks in a dual air brake system). It shows the amount of air pressure in the service tank.

Not quite. The answer is the brakes to fade.

Excessive heat caused by overuse of the brakes can expand the brake drums away from the brake pads or shoes and affect the brake linings, reducing friction. The brakes will fade (lose their effectiveness). On a long or steep downgrade, rely on engine braking more than the service brakes.

Not quite. The answer is It supplies compressed air from the service tank with the highest pressure.

A two-way check valve allows compressed air from two different sources to flow through the same air line. The valve will select the source with the higher pressure. In this case, a two-way check valve is connected to both the primary and secondary service tanks to always draw air from the tank with the higher pressure and send it to the parking brake control valve. This arrangement ensures that the higher pressure is available to release the spring parking brakes. It also ensures that the spring parking brakes will not activate if pressure is lost in just one of the two tanks.

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 Park on level ground, turn off the parking brakes, and pull hard on each slack adjuster.

To check the slack adjusters, try to pull on them manually while wearing gloves. If there is an inch or more of "give," then there is an issue and they should be fixed.

Not quite. The answer is 150 psi.

The safety valve, which protects the system from excessive pressure, is usually set to open when the system reaches 150 psi.

Not quite. The answer is 1 inch

The slack adjusters won't move if the parking brakes are on. To check the slack adjusters, park on level ground, chock the wheels, and then release the parking brakes. Use gloves and pull hard on each slack adjuster that you can reach. If a slack adjuster moves more than about one inch where the pushrod attaches to it, it probably needs adjustment.

Not quite. The answer is They work as a supplement to the braking effect of your engine.

When you drive down long, steep downgrades, the braking effect of your engine is what's most important, and your brakes are only a supplement to being in the proper low gear. They cannot compensate for your vehicle being in an unsafe high gear without putting too much pressure on your brakes.

Not quite. The answer is Every time you leave your vehicle, with a few exceptions

You should always use your parking brake except when the brakes are very hot or they are wet and at risk of freezing.

Not quite. The answer is They are springs that apply the brakes if air pressure drops too low.

Spring brakes are an important backup system: powerful springs that automatically apply the brakes if they sense that air pressure has dropped too low for effective braking. The spring brakes are also used as parking brakes.

Not quite. The answer is you have to press the brake pedal harder than usual to control your speed.

If your brakes begin to fade, you'll notice that you have to depress the brake pedal harder to achieve the same braking effect as before. If your vehicle is so equipped, check the application pressure gauge to see just how much pedal effort you are employing. If the brakes continue to fade, you may not be able to slow down or stop at all.

Not quite. The answer is 2 psi per minute.

One of the tests you must make of the air brake system is a test of the leakage rate without the foot brake applied. Fully charge the air brake system, turn off the engine, and release the parking brake. The air pressure should not drop more than 2 psi per minute for a straight vehicle or 3 psi per minute for a combination vehicle. If it is greater, check for leaks in the system.

Not quite. The answer is Whenever your vehicle is parked

You should always use your parking brake except when the brakes are very hot or they are wet and at risk of freezing.

Not quite. The answer is Do all of the above.

To ensure that your vehicle will be safe when you leave it unattended, apply the parking brakes and chock the wheels. Removing the keys is a simple safety tip for any vehicle, even a passenger car.

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

The parking brake control allows you to evacuate air from the brake chambers. With the air gone, the spring brakes will come on automatically and hold your vehicle in place.

Not quite. The answer is The dashboard air pressure gauges won't drop when it's drained.

It may be difficult to visually identify the supply tank. Instead, remember that your dashboard air pressure gauges monitor the air pressure in the primary and secondary service tanks. (In some vehicles, there are two gauges, one for each service tank; in other vehicles, there is one gauge with two needles.) Draining the service tanks will cause the gauges to show a drop in air pressure in those tanks. The supply tank is the tank that does NOT drop the gauges when it's drained.

Not quite. The answer is 32 feet.

When you depress the brake pedal, it will take perhaps a half second for the air to reach the brakes. At 55 mph, your vehicle will travel about 32 feet in that time before the brakes kick in. This will add to your total stopping distance.

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.