What do I need to know about air brakes?

Gib3633 wrote:
Fire up: Most of what you said OK except the slacks where you have to depress the collar to adjust are manual slacks. The other problem everyone wants to adjust there slacks but no one mentions the fact that there are regular stroke chambers and long stroke chambers and almost all chambers or cans as most of you call them have a different allowable stroke length. So you first have to be able to identify your equipment and know the procedure for measuring and know the individual specs before thinking about working with this. It is so much simpler to pay a certified tech.

Gib,
Roger that. I know, realize and stated that most of what I wrote down was the "basics" of air brake systems and, slack adjusters in and of themselves. Yep, there are different kinds of slack adjusters and, brake cans etc. We had multiple sizes and types of brake cans on our fire trucks and we too had to properly identify what we had before any forms of adjustment was made.

I didn't want to get too technical as like I said earlier in the air brake portion of what I wrote, there's a lot more to the systems than what I put down. I just tried to get the basic theory down and, the basic parts/components of the system. Thanks for the correction.
Scott

Fire up: Most of what you said OK except the slacks where you have to depress the collar to adjust are manual slacks. The other problem everyone wants to adjust there slacks but no one mentions the fact that there are regular stroke chambers and long stroke chambers and almost all chambers or cans as most of you call them have a different allowable stroke length. So you first have to be able to identify your equipment and know the procedure for measuring and know the individual specs before thinking about working with this. It is so much simpler to pay a certified tech.

I've found this manual to be very helpful.AIR BRAKE MANUAL
There is a pre-trip brake inspection on Page 85 that will confirm your brakes are working properly. Only takes a minute or two.

If automatic slack adjusters need to be adjusted they require service before use.......

rdmike wrote:
Thanks scott, i too now know 200% more than I did.

How do I know if I have slackers and if I do, how do you adjust?

rdmike,
Well Sir, your sig or your profile does not say what year your coach is but, based on its model name alone, it's fairly new. And that would just about guaranty that you have AUTOMATIC slack adjusters. I'm no expert, not by any stretch but, been around this stuff for decades and, have learned quite a bit by just being around it. I'd say that, based on all kinds rules and DOT specs and all that, I'd just about bet my house, (and I REALLY like my house) that every air braked motor home chassis made in the last 10-15 years or more, has been outfitted from the factory with automatic slack adjusters.

Now, you ask about how to adjust them. Well, as the name implies, they are BASICALLY self adjusting. But, there's a bit more to it in reality. You see, in order for those self adjusters to ADJUST, there must be enough wear on the shoes, to allow for a certain amount of travel in the brakes against the drums. That means they "wore" a tiny bit.

Now, without getting ultra technical here, it works this way. Those slack adjusters are attached directly from the brake can shaft (also known as the PUSH ROD), to the S-cam mechanism in the operation. As you apply the brakes, the diaphragm in the cans travels out and, therefore pushes on the top of the slack adjuster. That slack adjuster is like a minute hand on a clock. If you push on the top end, you have a ton of leverage on the other end of that minute hand. Well, that's how you get the amount of force, needed to push the brakes against the shoes, understand so far?

Well, the slack adjusters also have another component attached to the same "push rod" coming from the brake cans. (at least some of them do, and some don't) And that separate component is linked to "gear drive mechanisms" inside the slack adjusters. While that other component does absolutely nothing in applying the brakes, it's the part that, internally, MOVES gears, pawls, etc. that actually change the way that "Minute hand" is positioned, in distance, from the face of the brake can. Hope this is making sense so far.

So, if that alternate component travels far enough when you apply the brakes, (meaning the brake shoes have wore just a tiny bit) it, in turn (no pun intended) turns the mechanisms inside the slack adjuster to "ratchet" to the next closest position, to make the "throw" a shorter throw. It's complicated but, easy to understand, once you see how it works.

Now, Ok, here's where it gets sticky, in a sense. You can, MANUALLY adjust them, in two different ways.


First off, if you've NEVER HAD ANY EXPERIENCE IN THIS KIND OF THING, DO NOT TRY IT WITHOUT SUPERVISION FROM SOMEONE WHO HAS IT!!! This is your BRAKES you're messing with, care must be taken when goofing around with them, PERIOD!

It's not hard, or even that technical. It is in fact, just like adjusting the "star" wheel on a regular vehicles brakes, only you do it a bit differently. On one side of the slack adjuster is a small collar with a nut sticking out of it. That collar is spring loaded. It can be pushed in. When it is, that allows the nut, inside it, to be turned. If it's not pushed in, the nut cannot turn.

By turning that nut, ever so slightly, you are essentially doing a manual adjustment of the automatic slack adjuster. Now, the second way of MANUALLY adjusting them is, if there's enough play or, THROW in the brake push rod movement, you have to push on the brake pedal hard enough to allow for the "extra" component to sense that there's TOO MUCH THROW IN THE SYSTEM, and therefor, it will automatically ratchet itself, to DECREASE the throw, on the next application of brakes.

Once that's done, it (the slack adjuster) will remain at that adjustment, for however many amount of miles, until the brakes are worn a tiny bit more, and the system SENSESS it needs another adjustment.

So, you see, all this is being done, without your knowing it. Again, there's a bit more to this than I'm telling here but, that's the basic operation of an AUTOMATIC SLACK ADJUSTER. Hope this helps some. To any of you seasoned vets, aka Techs, Mechanics etc. if you're reading anything here that I'm not saying correctly, PLEASE correct me. Again, I'm not an expert, just old.
Scott

P.S. If you cut and paste the link below in an alternate browser, you'll see an image of a automatic slack adjuster. There are a few out there but, this is a basic image.


http://www.anythingtruck.com/commercial/images/421-AutoSlack.jpg

Don't forget to put that clothespin under the brake knob when parked. IN my previous post disaster strikes, lack of this little tidbit of knowledge has cost my insurance company over 22k, me 500 for the deductible, and worst part is being full time, we get to live at the body shop for 2 weeks. Lots gen time as they can offer only an 15 amp extention cord.

s N s wrote:
Thanks Scott. Probably the best bit of advice made as simple to understand that you can find and read. I once was told on this site in a conversation "it's what you don't know about air brakes that can kill you". Again there was some real informative reading there as well. The problem is the people that don't have the slightest clue of the system and how it operates to keep themselves and anyone else around them safe with it's operation. Well done. Thanks!

When I read up on the air brakes it mentioned that everything newer than 1998 (I think) was required to have automatic slack adjusters.

Thanks Scott. Probably the best bit of advice made as simple to understand that you can find and read. I once was told on this site in a conversation "it's what you don't know about air brakes that can kill you". Again there was some real informative reading there as well. The problem is the people that don't have the slightest clue of the system and how it operates to keep themselves and anyone else around them safe with it's operation. Well done. Thanks!

Thanks scott, i too now know 200% more than I did.

How do I know if I have slackers and if I do, how do you adjust?

Calif doesn't require any testing unless your over 40 ft. Even then there is no test for air brakes, but they do walk you through the process during the Class B testing. If you 40 ft and under then no special license is required, even if it has air brakes. So unless drivers take it upon themselves to learn about air brakes, they aren't required to know anything.
Why they don't require an air brake endorsement is beyond me. They not only function differently than hydraulics, their maintence and application techniques are different. Kudos to those who ask such questions and to those capable of giving such great answers. I myself was quite clueless until I began studying up for the test even though it wasn't required.

To all those who made nice comments to my post,
I most certainly want to thank all of you for that. Very much appreciated. I sometimes get a bit "long winded" in some of my explanations of things on here but, based on the way the OP presented his question and, from his statement(s), I wanted him to get as clear of a picture as I could present, without going into much of the infinite detail of air systems and more.

And, yep, I wanted to add the "low air warning" buzzer etc. info but, I elected to leave it out because I was over loading with info anyway. My thoughts were/are, I gave the real basics of how things work. If he likes what he reads and, WANT'S to know more, then go to some of the manuals and websites out there and he can read 'till his hearts content.

I have been chastised before because I presented that much information on a particular subject. Again, I just want the OP to know and realize what's going on so that he/they, have a better understanding and, that MIGHT help to analyze a problem if and when crops up. Thanks again to all. Hope the OP has a better "feeling" for the operation of his brakes and all that's tied to them.
Scott

P.S. By the way, yep, it was mentioned that, if you get a low air warning while cruising down the interstate, do one thing immediately! And that is, CHECK YOUR AIR PRESSURE GAUGES. Note where they are when you first glance at them and, where they are in a matter of a few seconds etc. This will give you time to think and, make that move to get to the side of the road, depending on how fast those air pressure gauges are descending.

I'm sure all of you have seen the FOUR skid marks that start in the right lane and, rapidly move to the side of the road. Yep, that truck DEFINITELY LOST AIR rapidly. And, also as stated, HERE COME THE REAR BRAKES.
Scott