Free Air Brakes CDL Practice Test

 

Which of the following should you do before leaving your vehicle unattended?

Chock the wheels
Put on the parking brakes
Remove the keys
All of the above
   

How would you check your truck's slack adjusters?

Accelerate, then brake hard
Use gloves and pull hard on each slack adjuster you can reach
Press the brake pedal while listening for any strange noises
All of the above
   

Which of the following is true about your brake function if your ABS fails?

You will have no brake function and the truck will be out of control
You will still have normal brake function and simply need to get the ABS repaired soon
It may cause problems with other mechanical systems and there could be a huge fire risk
It will slow your truck to a halt and force you to pull over
   

Slack adjusters are:

Between the power screw and push rod on disc brakes
Part of your air brake system used to adjust the brakes
Between the push rod and S-Cam on drum brakes
All of the above
   

How do brakes work on a long, steep downgrade?

Not applicable - there is no breaking effect involved in a downgrade
As the main braking mechanism
As the main braking mechanism, with the engine braking effect as an emergency back-up
As a supplement to the braking effect of your engine
   

Spring brakes are:

Made up of powerful springs that are held in back while you are driving by air pressure
Brakes that come on automatically on a truck or tractor when the PSI drops too low
Not going to have full effect until your PSI drops to a certain range, often 20 to 30 PSI
All of the above
   

If the brakes are wet, what can be done to dry them out?

Use the brakes to slow down from a high speed
Drain the air storage tanks
They must be serviced by a mechanic
Use the brakes lightly while driving in a low gear
   

What should you never do when the spring brakes are on?

Check the air in the air tanks
Use the modulating valve
Press the gas pedal down
Push the brake pedal down
   

Most heavy-duty vehicles have a dual air brake system. What is a dual air brake system?

Two air brake systems with separate sets of controls
Two air brake systems that share the same set of air tanks
A primary air brake system for everyday use and a secondary air brake system only for emergencies
Two separate air brake systems that use a single set of brake controls
   

Before driving a vehicle with a dual air system, the driver must allow what to happen?

There are no special circumstances for a dual air brake system
The air compressor to build up a minimum of at least 100 PSI in the primary system
The air compressor to build up a minimum of at least 60 PSI in both the primary and secondary systems
The air compressor to build up a minimum of at least 100 PSI in both the primary and secondary systems
   

Which of the following is true about a dual air brake system?

One is called the primary system and one is called the secondary system
One system usually operates the front axle and one operates the rear axle
They use a single set of brake controls
All of the above
   

What is the correct way to slow a large vehicle down on long downgrades?

Using a low gear and driving more slowly
Using exhaust braking
Holding the brakes down firmly
Controlled braking
   

Pressing on the brakes as hard as you can, releasing when they lock up, then pressing the brakes fully again when the wheels are rolling is called what?

Anti-lock braking
Stab braking
Impact braking
Controlled braking
   

In a dual air brake system, which parts of braking does each system typically operate?

One system operates the brakes on the rear axle/axles, the other operates the regular brakes on the front axle and the trailer
One system operates the brakes on the rear axle/axles and the trailer, the other operates the regular brakes on the front axle (and possibly a rear axle
One system operates the brakes on the front and rear axles, the other operates the brakes on the trailer (and possibly a rear axle)
One system operates the brakes on the rear axle/axles, the other operates the regular brakes on the front axle (and possibly a rear axle). Both supply air to the trailer
   

With air brakes, there is an added delay when stopping. What causes this?

The time required for the air brake system to measure the correct amount of pressure to send to each wheel
The time required for the compressed air to engage the push rod
The time required for compressed air to build up enough pressure to engage the brakes
The time required for the air to flow though the lines to the brakes
   

Where is compressed air stored?

Air compressor
Pressure gauge
Main reservoirs
Service and emergency air lines
   

To test the air leakage rate, one must turn off the engine (with a fully charged air system), turn the key to the on position, release the service brake, and do what?

Measure the PSI as the air pressure gauge falls from its original amount
Time how long it takes for the air compressor governor to cut in
Measure the amount of pressure in the system, then come back in about 30 minutes and measure the pressure again
Time the air pressure drop
   

Chemical changes in the brake lining, which reduce friction and cause expansion on the brake drums is known as what?

Brake fade
Green fade
Surface scorch
Brake overheating
   

Which of the following is a reason that air tanks must be drained?

Your left side brake will cease to operate
You will drive too quickly if they are not
Your brakes may fail due to the water freezing
Your transmission fluid may drain out
   

Why is it especially important to have your brakes adjusted before going down steep grades?

Some brakes will do more work than others
It is not any more important than at any other time
It can cause your slack adjusters to fail
It will cause more of a strain on the air compressor
   

In what instances should you not use the parking brakes when parking?

When the emergency brake is turned on
If the brakes are very hot or very wet in freezing temperatures
If you are on level ground
Always use the parking brakes when parking
   

If parking brakes are not being used when the vehicle is parked, what must be done instead?

Use wheel chocks
Parking brakes must always be used
Use the emergency brakes
Leave the vehicle in gear when parked
   

Which device allows you to remove oil and water from the air brake systems?

Air tank drain
Safety valve
Alcohol evaporator
Treadle valve
   

What does it mean when the safety valve opens and releases air?

The pressure has exceeded 150 PSI
The system is fully charged
Something is wrong, a mechanic needs to check it
The pressure has exceeded 150 PSI and something is wrong, a mechanic needs to check it
   

If you press and release the brake pedal rapidly, what will happen?

You can let the air out faster than the compressor can replace it
Your vehicle will stop faster and straighter
You can safely control your speed around a curve
You can cool your brakes rapidly
   

Which device helps reduce the risk of ice in the air brake systems during cold weather?

Air compressor governor
Air tank drain
Safety valve
Alcohol evaporator
   

What is modulating control valve?

A device that controls when the air compressor will pump air into the air storage tanks
A device that cuts the normal air pressure to the front brakes by half
A valve used to drain oil and water from the air storage tanks
A lever used to apply the spring brakes gradually
 
Check Answers
 

Ready to Apply for on-the-job CDL Training?