Learning The Air Brake Test For The CDL Examine

Topic 3795 | Page 1

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Randall H's Comment
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While this test is not difficult, it is something MANY MANY students are messing up on their CDL exam. It is a Go-No Go part of the test. Fail this test and it is an automatic failure of the entire exam. It does not make sense that so many student drivers would fail such a test, especially when it supposed to be done every day during the training period. It is my belief that besides the failure to do it every day and learn it by repetition, that many have a hard time with it because they are trying to do it by memorizing the words as they are given on their handout. But if you are not the type to do well at regurgitating memorized words, this can be a formula for failure. I believe there is a better way and that is what I am going to lay out for you now. This is about seeing the bigger picture of what’s going on, beyond the individual steps used to complete it. This is about understanding what is happening, not just the steps taken to make it happen. OK, here goes…..

At the end of your in cab inspection you should end with checking the service brakes by pulling forward at 5 mph and applying the service brakes to make sure they work and do not pull to the left or right. This sets the stage for preparing for the Air Brake Test. You are sitting there with your truck in low gear, the engine running, and the brake applied. Verify that the air pressure supply is in the range of 120-125 psi, turn the engine off and then turn the key to the on position, and release the Tractor Supply and Parking Brakes by pushing them in. Then wait for the air pressure to stabilize. You are now set up for the brake test. Now, instead of just quoting the steps to take, picture it this way. Picture the air pressure gage, at full pressure right now. As you do your 3 stage test, you will be checking three things that involve pressures.

First you will check to make sure there are not leaks that cause the pressure to drop by more than 4 psi in 1 minute. This happens with the needle on the air gage near full pressure. We don’t want leaks that would deplete the air supply, so we need any drop in pressure to be minimal. Therefore it should not drop more than 4 psi during 1 minute.

Then you will test the alarm which must come on at or before reaching 60 psi. In case a leak should develop while we are driving, we want to know about it. We DO NOT want to find out when the Tractor Supply and Parking Brake valves pop out!!! So, there is an alarm BEFORE it gets that low. Therefore the alarm light and buzzer are set to comeon before it drops too far…….AT OR BEFORE 60 psi.

Then you will verify the Tractor Supply and Parking Brake Valves pop out in the range of 40 – 20 psi. Should there be such a big leak that you are unable to get pulled over and stopped using the service brakes, the truck is designed to apply the emergency brakes when the pressure drops to between 40 and 20 psi. The valves pop out and the spring applies the brakes.

Picturing it this way, from normal operating range to an emergency situation of the brakes being applied automatically will help you grasp what exactly is happening during the air brake test. So, picture the gage with full air, testing it for leaks that result in no more than 4 psi loss in 1 minute, then dropping to test the alarm buzzer and light, and then testing the valves popping out. So, how do we go through this from top to bottom? How will you check the pressure for stage 1? You will hold the brake fully down for 1 minute, timed.

How will you get the pressure all the way down to 60 psi to test the alarm? You’ll have to pump it down because each time you step on the brake pedal air is used and released from the system, causing the air pressure to drop. (Remember…the truck is NOT running so the air compressor will NOT come on to restore pressure)

How will you further reduce it to between 40 and 20 psi to test the valves? You will keep pumping it down. Continued on next post.....

CDL:

Commercial Driver's License (CDL)

A CDL is required to drive any of the following vehicles:

  • Any combination of vehicles with a gross combined weight rating (GCWR) of 26,001 or more pounds, providing the gross vehicle weight rating (GVWR) of the vehicle being towed is in excess of 10,000 pounds.
  • Any single vehicle with a GVWR of 26,001 or more pounds, or any such vehicle towing another not in excess of 10,000 pounds.
  • Any vehicle, regardless of size, designed to transport 16 or more persons, including the driver.
  • Any vehicle required by federal regulations to be placarded while transporting hazardous materials.
Randall H's Comment
member avatar

So, here goes….stage 1

Mr. Examiner, I will need you to help me with this by timing me for 1 minute while I firmly hold the brake pedal down, during which time the air pressure should not drop more than 4 psi while I am also listening for air leaks.

Stage 2 I am now going to pump down the brakes until the alarm buzzer and light come on which should occur at or before the air pressure reaches 60 psi.

Stage 3 I am now going to continue to pump down the brakes until both the Tractor Supply and Parking Brake valves pop out which should occur between 40 and 20 psi. IMPORTANT NOTE!!!!

If during this test you realize you made a mistake……….stop and tell the instructor you are going to start over. This is allowed. Then go back to setting up for the test by starting the truck and letting the air compressor build the air pressure to 120 to 125 psi. You are allowed to do it over!!!

If your examiner should ask you if your test is complete, know that he may be asking you to give you a friendly hint that you missed something. He can NOT tell you that you made a mistake, but he can ask you if that completes your test. If he does this, starting over would be a great idea because if you miss even one thing on the test, YOU FAIL!!! If you get it right twice, GREAT!!!

There is nothing that stops you from doing it over. It is not timed. They just want to make sure you know how to do the entire thing 100% right. If that means repeating it, then great, repeat it. But saying you are done and you’ve missed something……..not good at all.

So, learn the big picture and what is actually happening with each stage of the air brake test and it will be a lot easier to remember the stages, how they are done, and what the results should be. That’s how to “BRAKE” it down!

Hope this helps you.

TWIC:

Transportation Worker Identification Credential

Truck drivers who regularly pick up from or deliver to the shipping ports will often be required to carry a TWIC card.

Your TWIC is a tamper-resistant biometric card which acts as both your identification in secure areas, as well as an indicator of you having passed the necessary security clearance. TWIC cards are valid for five years. The issuance of TWIC cards is overseen by the Transportation Security Administration and the Department of Homeland Security.

Daniel B.'s Comment
member avatar

Bravo Randy, Bravo!

Hope you're doing well!

Schism's Comment
member avatar

Shouldn't a static air check verifying that an air loss of no more than 3 psi happen before the service air ( 4 psi ) check ?

-s-

Randall H's Comment
member avatar

Shouldn't a static air check verifying that an air loss of no more than 3 psi happen before the service air ( 4 psi ) check ?

-s-

I understand where you are coming from but it is NOT a part of the test on the exam.

Tarren W.'s Comment
member avatar

Thanks, Randy!!! It's funny because I was just going through the air breaks portion of the High Road program, and I was having a little bit of trouble visualizing the steps of actually doing it.

Great post!

Tarren

Randall H's Comment
member avatar

Bravo Randy, Bravo!

Hope you're doing well!

Thanks Daniel. I am doing great. Learning to do the back up maneuvers tomorrow. My instructor said I am doing very well after 1 week. I'm really pumped up and should have my license in hand in 2 weeks. Hope things have smoothed out for you after your rough time off. Holler at me when you get here....if you come here.

Serah D.'s Comment
member avatar

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Shouldn't a static air check verifying that an air loss of no more than 3 psi happen before the service air ( 4 psi ) check ?

-s-

double-quotes-end.png

I understand where you are coming from but it is NOT a part of the test on the exam.

Wow...it is part of the test in NJ. Looks like there's a difference the training and testing in NJ.

Randall H's Comment
member avatar

double-quotes-start.png

double-quotes-start.png

double-quotes-start.png

Shouldn't a static air check verifying that an air loss of no more than 3 psi happen before the service air ( 4 psi ) check ?

-s-

double-quotes-end.png

double-quotes-end.png

I understand where you are coming from but it is NOT a part of the test on the exam.

double-quotes-end.png

Wow...it is part of the test in NJ. Looks like there's a difference the training and testing in NJ.

Even so, the concept remains the same and that step of the test would be added in at the appropriate place. The main point is seeing the bigger picture of what is happening instead of just memorizing a set of words.

Peggy 's Comment
member avatar

Thank you Randall.

I am preparing to start CDL school next week (hopefully). I took my CDL permit test and passed all but "Air Brake" portion; by one question.... I too came across two "Air Leakage" test questions on my permit testing....it seems there are two "Air Leakage" tests; an Applied and Static testing. The CDL manual I have only clearly defines; Applied Leakage.....in the permit testing I was asked for both....lol. I have questioned seasoned drivers but I was unable to get a definite answer on Static....they all knew Applied.

So my dilemma and question is what is the difference between Applied Leakage Testing and Static Leakage Testing and How are they properly performed during a pre-trip inspection?

Help!! Peggy (Philadelphia)

Pre-trip Inspection:

A pre-trip inspection is a thorough inspection of the truck completed before driving for the first time each day.

Federal and state laws require that drivers inspect their vehicles. Federal and state inspectors also may inspect your vehicles. If they judge a vehicle to be unsafe, they will put it “out of service” until it is repaired.

CDL:

Commercial Driver's License (CDL)

A CDL is required to drive any of the following vehicles:

  • Any combination of vehicles with a gross combined weight rating (GCWR) of 26,001 or more pounds, providing the gross vehicle weight rating (GVWR) of the vehicle being towed is in excess of 10,000 pounds.
  • Any single vehicle with a GVWR of 26,001 or more pounds, or any such vehicle towing another not in excess of 10,000 pounds.
  • Any vehicle, regardless of size, designed to transport 16 or more persons, including the driver.
  • Any vehicle required by federal regulations to be placarded while transporting hazardous materials.
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