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Old 07-06-2011, 04:52 PM   #1
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Why an Air Brake Endorsement?

I know that in many areas, operating a rig with air brakes requires some combination of special training, testing, and licensing. I did it when I got my Texas non commercial Class B license but I believe the main factor there was the weight of the rig rather than what type of brakes it had. I believe that some other areas require this testing before operating ANY vehicle with air brakes.

What I have wondered is, why is there apparently such a focus on the need to know the inner workings of air brakes?

From what I (think I) know about air brakes, they seem to be a far safer method of controlling your vehicle than conventional brakes. If a hydraulic line breaks on conventionals... aren't you kind of in trouble and have to rely on a mechanical "parking brake" for just the rear wheels? With air brakes, won't a broken air line or failed compressor automatically release the pressure on the brake springs and stop all four (six) wheels?

To prepare for my test, I read my manual and the Texas handbook and before starting out in the morning I will pump my brakes several times to ensure I see the compressor kick in and recover pressure. It was good reading and I enjoyed the additional information I learned but why is this level of knowledge felt to be more important for air brakes than for hydraulics?

Thanks for your thoughts.

Rick
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Old 07-06-2011, 05:00 PM   #2
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The reason you need to know how air brakes work, is because that on semi trucks they work a bit differently than what you might expect. As it happens, I've read the book and thus understand this.. However I did not "Study for the test" as I was not taking it.. I just read the book because I was bored and it was handy.

So though I can't tell you all the differences.. I do recall that there ARE differences. for one there is the precision delay before trailer brakes come on on a semi.

Under the law. Air brakes are Air brakes, Semi or Motor home, not always distinguished. (Sometimes but not always)
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Old 07-06-2011, 07:21 PM   #3
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Mainly because you need to know the warning signs (gauge, buzzer) of low air pressure, what to do about it, and what happens if you loose it entirely. Very different than what happens with hydraulic (automotive) brakes.

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Old 07-06-2011, 07:42 PM   #4
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I agree with FlyingDiver. A person that drives a vehicle with air brakes needs to know the air pressure level that is required to operate air brakes, needs to know how the parking brake works and all the other items that go with air brakes. Funny thing is that when I took my Class B non-CDL I was NOT required to explain all those items or even test on them. The examiner prompted me to test each item and while I tested the hardware I was not required to test them without the prompts... I asked about that and she said that in Texas even though I was driving a motor home with air brakes I was not required to test on those items as I did not need a air brake endorsement!
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Old 07-06-2011, 07:51 PM   #5
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I also think that there needs to be a "Modified" Air Brake Course for Drivers of RV's equipped with Air Brakes ,as opposed to the Operators of Heavy Trucks.

I'm not sorry that I took the Course as I have some interest in Big Trucks and sometimes get to drive them , not for Hire ! The difference between doing a Pre trip on a Motorhome is considerably different from what is required on a Semi!
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Old 07-06-2011, 08:22 PM   #6
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Rick....in most Canadian Provinces an air brake endorsement on your driver's licence is required. Why....? No idea other than I personally think it is a good idea, since most of us are unfamiliar with this type of brake system when we purchase and get involved with larger Coach style MH. The course's teach the principles of the system and the proper way to test your brakes. Seems like a pretty good idea to know something about and how to test the integrity of your brakes if you are going to safely operate a +30,000lbs vehicle. In addition, you'll also know "what" those two gauges on your dash are for ....& "why they move & what they should read"

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Old 07-06-2011, 08:39 PM   #7
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Quote:
Originally Posted by RickO View Post
... With air brakes, won't a broken air line or failed compressor automatically release the pressure on the brake springs and stop all four (six) wheels?...
The rear brakes on each side of the drive axle are the only ones operated by the spring actuators when you lose air pressure (or pull out the yellow brake knob).
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Old 07-06-2011, 09:41 PM   #8
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Thanks all. It still seems to me that the real reason many laws require some form of air brake knowledge is because of the size of what we're driving and the potential damage we could do.

If I get a drop in pressure warning... I'm getting off the road now! If my automotive brake pedal turns to mush... I'm getting off the road now... yet I don't need to know about hydraulic fluid and master cylinders to get a license to drive a car.


Quote:
Originally Posted by cbeierl View Post
The rear brakes on each side of the drive axle are the only ones operated by the spring actuators when you lose air pressure (or pull out the yellow brake knob).
Thanks, I hadn't realized that.

Rick
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Old 07-06-2011, 09:57 PM   #9
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Last month I completed the seminar at Freightliner, Gaffney, SC. One of the things I was impress with was the demonstration Mike Cody gave on the "yellow knob", when used in an emergency. We were in the Freightliner bus, and as he was taking members back to their campgrounds he gave two demonstrations. First, at about 30-35 mph he applied the foot pedal brake relatively hard, or full. The coach came to a very abrupt stop without locking up the tires. Then at about 45 mph he pulled the "yellow knob." The coach came to a rolling stop, not as abruptly as when the foot pedal was applied. I was surprised. I thought there would be a screeching halt, but no, it was much gentler then applying the foot pedal full force.

So, if you are going down the highway and someone pulls out in front of you and you think pulling the yellow knob will stop you quick, you have another think coming. However, if you are going down the highway and suddenly become to ill to drive, have DW elbow you back to a sitting position, turn off the cruise control, hold on to the steering wheel to guide the coach, and pull the Yellow Knob. She will maintain control and the coach will come to a rolling stop.

Now, should you be on the highway, what do you supposed may happen if your ASA (Automatic Slack Adjusters) fail to adjust. Would you know how to do it, or would you just continue with a possible unsafe condition? So it is not just about air pressure and gauges, but mechanical in nature also. It really should be in everyone's repertoire that has air brakes to understand how they work, and how to adjust them should the need arise.

Happy trails.
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Old 07-06-2011, 11:12 PM   #10
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I believe Wayne has hit on the central reason, slack adjusters were not always automatic, and the cause of many accidents was not loss of brakes but loss of adjustment. I think this is the main reason for the air ticket requirement.
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Old 07-07-2011, 12:04 AM   #11
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Srydve, I believe you are right, it is a hold over from the "old days", before Automatic Slack Adjusters" were the norm, as they are now (required on all air brake equipped vehicles manufactured after Oct 20, 1994). As for adjusting the Automatic Slack Adjusters this link (though a little tongue in cheek) says it all.

YouTube - ‪AIR BRAKE ADJUSTING AUTOMATIC SLACK ADJUSTERS‬‏

As for pulling out the Yellow Knob, it is the parking brake and only applies the rear brakes, thus, it would not stop the vehicle near as effectively as applying ALL the brakes, both rear and front, with the brake pedal. The Freightliner Manual indicates that the Automatic Slack Adjusters should not be adjusted until the underlying cause is addressed first. And in either case, IMHO, is not a normal DIY type of maintenance.
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Old 07-07-2011, 12:43 AM   #12
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If you live in B.C. and your driving an air brake equiped vehicle without an endorcement. YOU ARE DRIVING WITH NO INSURANCE ! Left out of the thread so far is the proper maintenance of the air tanks, even with the heated de-humidifiers in place and automatic blead valves in place , F/L manuals say to manually blead the tanks and check for water in the system.
Having read that in the manual, I was shocked that the manual pull cables were still wraped up on the top of the tanks on an 11 year old coach. I guess F/L doesn't require the coach builders to route the cables out for owner access. Also knowing how to test the operation of the auto-slack adjusters, you can figure out if they're not doing there job before you have no brakes.
Yes there was a small amount of water in the tanks when manually drained.
Manual draining of the tanks is a test of the proper operation of the automatic drains.
When I first joined iRV2 one of the first threads I read was about someone who had rapidly dropping air pressure in the system, tanks full of water and the whole system full of rust . I can't find the thread, but I think the amount for repairs was $10,000.Understand your air brake system and keep it maintained , lives depend on it.
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Old 07-07-2011, 01:17 AM   #13
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RickO, a little asside if I may. For those of us old enough to remember, the early days of automotive Hydraulic brakes.They weren't always so trouble free. My first car had Hyd.front brakes and linkage rear brakes.So if the single fluid resivoir went dry there was a back up system. Having worked on brakes during the ongoing development of the automotive systems. From manually adjusted drum brakes to four wheel disc with anti-lock, it's been quite a trip. Maybe, though if driver training for cars required a complete understanding of the systems of the car ; brakes in particular, we'd have fewer accidents. At least if every one knew where to check their brake fluid and how to recognise the signs of fliud loss. Just MHO. Skip.
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Old 07-07-2011, 08:46 PM   #14
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Thought I would bring to light that new Disc Air Brakes are now available on Semi and Heavy Truck Applications. They have been tested and shown to reduce stopping distance by up to 35% with just front disc alone.
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