Wisconsin CDL: Air Brakes Practice Test

Not quite. The answer is air pressure.

Spring brakes contain powerful springs that are normally held back by air pressure. If the pressure drops too low, the spring brakes will automatically kick in.

Not quite. The answer is glad hands

As part of your vehicle inspection test, if your vehicle is equipped with air brakes and has a trailer, you will inspect the air connections between the truck or tractor and the trailer. These connections are made with hose couplers (commonly called "glad hands" because they vaguely resemble shaking hands). These glad hands have rubber seals to form a tight connection and prevent air from escaping. Make sure that the glad hands are locked in place and free of damage or air leaks.

Not quite. The answer is 125

The air compressor will start pumping air into the air tanks at about 100 psi and stop at about 125 psi. This action is controlled by the air compressor governor.

Not quite. The answer is Stop and park safely. Continue only after the system has been fixed.

A dual air brake system has two separate air brake systems, each with its own air tanks, hoses, lines, etc. Typically, one system operates the brakes on the rear axle(s), and the other system operates the brakes on the front axle. If one of the systems loses air pressure (causing the low air pressure warning), either the front or the rear brakes won't work properly. As a result, your vehicle's braking distance will increase. If this happens, stop your vehicle and get the system fixed.

Not quite. The answer is Otherwise, you will have to get a CDL with restrictions.

If you do not pass the air brake knowledge test, your CDL will include restriction L, which will limit you to driving vehicles without air brakes. So, good luck!

Not quite. The answer is Only if it's not working properly

Once properly installed and lubricated, an automatic slack adjuster should not need manual adjustment. If it does, it may be malfunctioning or there may be a problem with the foundation brake itself. Find the problem and correct it.

Not quite. The answer is Pressure-protection valve

Various auxiliary air systems, such as air suspension and the driver and passenger air seats, usually get their air from the service tanks of the air braking system. To prevent the tanks from losing air in the event of a leak or failure in an auxiliary air system, a pressure-protection valve is installed between each auxiliary air system and the service tank. If tank pressure drops below a preset level, the pressure-protection valve will close to stop any more air from flowing to the auxiliary air system.

Not quite. The answer is forces the brake shoes against the inside of the brake drum.

When the S-cam rotates, it forces the brake shoes apart and against the inside of the brake drum. Friction will slow the rotation of the wheel.

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

The tractor protection valve protects your air brake system by providing the air supply, closing automatically if the air supply drops too low, and closing if you apply the parking brakes.

Not quite. The answer is Never

Never leave your vehicle unattended without first applying the parking brakes or chocking the wheels. Your vehicle might roll away and hit something – or someone.

Not quite. The answer is brake lag.

When you depress the brake pedal on a vehicle with air brakes, there will be a lag of about a half second before the air flows through the lines to reach the brakes. This will add to your total stopping distance.

Not quite. The answer is brake in a straight line.

In controlled braking, you brake as hard as you can without locking the wheels. As you do this, keep your vehicle going relatively straight.

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 All vehicles with air brakes currently in operation must have low air pressure warning signals.

All vehicles on the road that have air brakes must have low air pressure warning signals.

Not quite. The answer is a loss of brake air pressure.

Each time you release the brakes, some compressed air leaves the system and must be replenished by the air compressor. If you keep pressing and releasing the brake pedal, air may leave the system faster than the air compressor can replenish it. The air pressure may drop to the point that the brakes won't work.

Not quite. The answer is park on level ground, chock the wheels, and release the parking brakes.

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 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 expansion of the brake drums.

Overusing the service brakes can cause overheating and expansion of the brake drums. The brake shoes will have to move farther to contact the brake drums, making braking harder or eventually impossible (brake fade).

Not quite. The answer is With ABS, you do emergency braking differently than without ABS.

Without ABS, hard braking can lock the wheels, resulting in a skid. Therefore, to do emergency braking without ABS, you should use the "stab braking" method or the "controlled braking" method. With ABS, go ahead and brake hard; the ABS computer will prevent your wheels from locking.

Not quite. The answer is to tell you how much air is in the tank.

The supply pressure gauge tells you how much air is in the tank at all times. In some vehicles, it may be connected to a warning bell or light.