Oregon CDL: Air Brakes Practice Test

Not quite. The answer is one-half

During your walk-around inspection, check the brake drums to be sure that no cracks are longer than half the width of the friction area.

Not quite. The answer is 3 psi per minute.

After the initial drop, the maximum acceptable leakage rates with the service brakes on are 3 psi per minute for single vehicles and 4 psi per minute for combination vehicles. If the leakage rate is higher, check for leaks and correct them.

Not quite. The answer is 35 mph.

On a steep downgrade, continuous application of the service brakes might cause them to fade (become less effective). Instead, apply your brakes sparingly as a supplement to engine braking. Select a "safe" speed. Let your vehicle reach this speed. Brake gently until you are going 5 mph slower. (In this case, with a "safe" speed of 40 mph, you should brake gently until your speed drops to 35 mph.) Then let your speed increase back to the "safe" speed. Keep varying your speed up and down this way. This technique is known as snub braking or snubbing.

Not quite. The answer is either (a) or (b).

If you need to stop quickly, use either the "controlled braking" method or the "stab braking" method. However, if your vehicle has antilock brakes, stab braking won't work because the wheels won't lock. Use controlled braking instead.

Not quite. The answer is Use gloves and pull hard on each slack adjuster you can reach.

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

Not quite. The answer is all of the above.

Slack adjusters are an important part of your air brake system that allows you to adjust the brakes to ensure that they are safe. They are located in different places, depending on the type of brakes that you have.

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 5 mph slower.

On a steep downgrade, don't keep applying your brakes continuously because this might cause them to fade (become less effective). Instead, apply your brakes sparingly as a supplement to engine braking. Select a "safe" speed. Let your vehicle reach this speed. Brake gently until you are going 5 mph slower. Then let your speed increase back to the "safe" speed. Keep varying your speed up and down this way. This technique is known as snub braking or snubbing.

Not quite. The answer is 3 psi in one minute.

When testing for an air leak, make sure the system is fully charged, turn off the engine, fully apply the foot (service) brake, and hold the brake for one minute. The air pressure should not drop more than 3 psi for a single vehicle or more than 4 psi for a combination vehicle. If it does, check for an air leak somewhere.

Not quite. The answer is that you are applying to the brakes.

If your vehicle is so equipped, the application pressure gauge will show how much air pressure you are applying to the brakes. If you have to apply more pressure than before to achieve the same braking effect, your brakes are fading (becoming less effective).

Not quite. The answer is Typically, one brake system operates the brakes on the front axle, and the other system operates the brakes on the rear axles.

A dual air brake system has two separate air brake systems, each with its own air tanks, hoses, lines, etc. Both systems are controlled by the one brake pedal. Typically, the secondary system operates the brakes on the front axle (and possibly one rear axle as well), and the primary system operates the brakes on the rear axles.

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.

Not quite. The answer is 2 psi per minute.

To test the static air leakage rate, turn off the engine, release the parking brake (i.e., push the parking brake control knob in), and see how fast the air pressure drops. The air pressure should drop less than 2 psi in one minute for a single vehicle and less than 3 psi in one minute for a combination vehicle.

Not quite. The answer is controls the air pressure applied to the service brakes.

The brake pedal controls the amount of air pressure applied to the service brakes. The harder the pedal is pushed, the more air pressure is applied to the brakes.

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 brake normally.

Antilock brakes will automatically keep your wheels from locking so you can brake normally.

Not quite. The answer is 60

The low air pressure warning light must come on before the air pressure falls below 60 psi. On some vehicles, the warning light will come on at a higher air pressure. Check the manufacturer's specifications.

Not quite. The answer is Turn the adjusting nut to move the end of the slack adjuster until the brake shoes contact the inside of the brake drum. Then turn the nut the other way to move the brake shoes away from the brake drum.

To adjust a manual slack adjuster, turn the adjusting nut so that the S-cam rotates in the same direction as when the brakes are applied. Keep turning the nut until the nut stops turning. At this point, the brake shoes should be pressing tight against the inside of the brake drum. Then turn the nut the other way about one-third of a turn to move the brake shoes away from the inside of the brake drum. Note: This procedure may not be described in your CDL manual.

Not quite. The answer is All of the above

A modern Air Dryer Integrated System (AD-IS) combines the governor, air dryer, and safety valve into one system. Compressed air from the air compressor goes to the AD-IS, which removes moisture and contaminants from the air. The clean, dry air then goes to fill the primary and secondary service tanks.

Not quite. The answer is at all wheels.

Foundation brakes are found at each wheel. The most common type of foundation brake is the S-cam drum brake.