M923a1 air brake question

[m16ty]

Air brake leaks can be tricky. You can have a relay leaking but something else could be causing the relay to leak (changing the relay won't fix the leak).

I've fooled with the M939 brakes a little. Best thing to do if the leak isn't something obvious is look over the air brake section in the TM really good to see how the system works and how to troubleshoot.

 

[Artisan]

C.O.L.A.

You HAVE to learn what this means. It is a HUGE responsibility driving these rigs
and the reasoning for getting a CDL is to make SURE you know how to TEST air brakes,
amongst other things. When you take the test at the Licensing Department, here in California,
it is the one part of the test where there are NO ERRORS ALLOWED. If you fail to prove
to the DMV examiner that you know what your doing ( COLA Test) the test STOPS, you burned one of
three fails and you come back another time, and they will remember you...

It is not that hard to learn this stuff and it is HUGE important! I just did it in 9 days at Dootson Driving School
in Arcadia California. I am SO GLAD I did NOT just go jump in that seat and go...
like I was told so many guys do. 9 days and maybe 600 bucks. They threw me in
a 36' long bus w/ Air brakes and handed me a study manual and some practice
tests.

COLA, learn it bro... If the truck fails a COLA test YOU PARK IT, period,
End of story, till it is fixed.

You wreck out w/o a CDL and you will loose everything in a court of law too plus
perhaps kill or mame someone as well. Go get educated, then come back and
re-read what you wrote and you will see why some of us a jumping up and down
suggesting you do the deeds bro... Your words would HANG YOU in a court of law
if something happened...

With all due respect...

 

[commandojeff]

How many times can he hear that he should get a CDL? Who cares if you have a CDL or not? The point of this thread is to help him out with getting his brake issue fixed. You do not need a CDL in every state to drive these trucks. I disagree with the fact that you should get a CDL. I do agree with reading the manuals, understanding your trucks, and being responsible. The bottom line is his truck isn't running right and he asked us a question.

I have not had any issues with my air system yet. So I can't help you with you losing air. I do know that you need to be careful with those springs if you have to replace your diaphragms. They are under extreme tension and can easily fly through you.

Be safe!
Jeff

 

[rosco]

On spring brake pots, its not just too uncommon for the big mean spring in there, to break. That usually results in a jagged end that usually punctures the diaphram. The resulting hole can be so massive that the air escaping , won't make much noise escaping. But I'm over thinking... The problem is only a massive leak, with foot on brake pedal. So spring side, should be OK. Would therefore be, the service brake side, if that it. Does the low air buzzer work?

 

[Farmallmilitary]

Like I told everyone I am planning on getting a cdl. I have literally driven this truck 3 times because I know there is an issue with the brakes I am just trying to resolve this problem. I am trying to learn as fast as I can about every system on it including its AIRBRAKE system. Also technically I dont have to have a cdl where I live and as long as I dont load the truck more than 26,000 pounds then I am good. The first time I drove it was putting it on a flatbed and I noticed something wrong with the brakes but thought I will fix it at home. Then I unloaded it and brakes still acting up then I took it for a small test drive NOT on any main roads ( I used the stoplight before as a comparison), just dirt roads and the problem was still there so I parked it and its been there since. I am not driving it anymore because I am have enough sense to not drive it with a brake problem. My main goal posting this thread was trying to figure out its brake problem, not be chewed out by ss members. Thanks to the others for the input though.

 

[quickfarms]

I am not going to chime in about the CDL issue other than saying you should read the manual especially the air brake section.

Below is a link fir an air brake manual that you should read.

http://www.gov.ns.ca/snsmr/rmv/licence/pdf/air_brake_manual.pdf

If you can not find the leak you should have a DOT certified brake technician go over the air system.

 

[doghead]

In your state, and most others, you must be 18 to get your CDL.

 

[Farmallmilitary]

Yeah I accidentally hit the six instead of the nine but I am actually elligible for a cdl.

 

[Artisan]

32,175 pounds is the GVW of an m923a1 yes?
the GCVW is I think 47175 !!! HUGE!

The truck weighs 22,175 empty and a 10K payload = GVW right?
So w/ your analogy your saying as long as you do not actually weigh more than 26000 your ok right?

Ummmm, I don't think so. If that were true every trucker would just lie and no one would have CDL's.

In the end I think it will be proven you need a Class B CDL w/ Air brake endorsement.
Each state has to conform to Federal regulations, they all have a means to the same end.
Otherwise it would be chaos!

That brings things full circle, if you have these credentials you would know why "the brakes came on by themselves"
instantly. You would have tested your brakes almost daily as well and the test would have shown
a leak, again COLA ( Cut Out Low Air ) It is part of the testing that keeps you and others around
you alive. Millions of guys have done it.

Lets say you find your leak. ( and I hope you do) You gonna be good w/ fixing just one leak?
How do you know there is not another leak, maybe a smaller leak, maybe SEVERAL?

COLA!

If I am one of the ones "chewing" just tell me and I will unsub...

 

[MyothersanM1]

Getting an air brake ticket is highly advisable, but it still won't answer all of the OP's questions. When I took my CDL training and passed my test, the training included the dash-mounted air brake controls used in common civilian semi tractors, and didn't cover anything like the combination air brake + mechanical driveline brake in the M939 series. It covered testing to see whether there is an air leak, but not how to diagnose where the air leak is. So the OP's question about the actuator on the parking brake lever would still be unanswered by the CDL training.

The parking brake lever on the right side of the driver's seat does two separate things:

1. The lever itself applies a mechanical parking brake in the driveline, just like in older MVs with air-over-hydraulic brakes.
2. The lever bumps that air valve behind it to control the spring parking brakes, which are RELEASED by air pressure, like on any normal air brake truck.

Since you need to be able to have the spring parking brakes released in order to tell whether the mechanical driveline parking brake is adjusted correctly, there's a round button to push on the dash to release the spring parking brakes. With that button pressed in, you can turn the knob on the end of the parking brake handle to adjust the mechanical driveline brake until it holds the truck. That knob is a fine-tuning adjustment to let the operator take up minor wear, and there's also a rough adjustment under the truck that needs to be in the right ballpark. The dash knob is only used for testing/adjusting the mechanical driveline brake, and it is left pulled out at all times in normal operation.

If air leakage can be heard from the engine air intake, then I've been told that's probably from leaking seals in the brake pedal valve which are allowing air to leak into the vent system. I have the same issue on one of my trucks, but I haven't dug in there to fix it yet (don't worry, the truck isn't going on public roads until I fix that).

How many times can he hear that he should get a CDL? Who cares if you have a CDL or not? The point of this thread is to help him out with getting his brake issue fixed. You do not need a CDL in every state to drive these trucks. I disagree with the fact that you should get a CDL. I do agree with reading the manuals, understanding your trucks, and being responsible. The bottom line is his truck isn't running right and he asked us a question.

I have not had any issues with my air system yet. So I can't help you with you losing air. I do know that you need to be careful with those springs if you have to replace your diaphragms. They are under extreme tension and can easily fly through you.

Be safe!
Jeff

I am not going to chime in about the CDL issue other than saying you should read the manual especially the air brake section.

Below is a link fir an air brake manual that you should read.

http://www.gov.ns.ca/snsmr/rmv/licence/pdf/air_brake_manual.pdf

If you can not find the leak you should have a DOT certified brake technician go over the air system.

I'm going to agree with all the above quotes. I'm not going to jump on the CDL bandwagon nor chastise the OP for not having one. But, I will encourage him to get right, legal and safe in his state.

That being said, the air brake test administered by DMV/DOT's does not prepare one to FIX air brakes only how to determine if they are up to being mission capable. On the other hand, the study materials will give one the basic understanding of operation. The OP wrote to ask for help in troubleshooting his air brake system. So, as fine upstanding Steel Soldiers whom are M939 savvy, please, step up and help out.

Study the TM. I own an M818, but I do frequently study the M939 series manuals JUST in case I get one someday...

 

[commandojeff]

I am 20 years old. The DMV didn't seem to have a problem with my truck having a 42,000 GVWR. I use my truck for PERSONAL use. No where in the MO CDL book says you are required to have one for personal trucks. Only states for commercial use. Now, is this the smartest thing, no. But if it isn't required, why waste the time and money getting one?

Be responsible, know your truck, read the manual, and help others.

 

[TMNT]

As far as the FMCSA (the Feds) are concerned, the laws governing commercial vehicles apply only to vehicles that are engaged in interstate commerce. Privately owned vehicles used for personal use only and not used for any commercial purpose, aren't "commercial vehicles" regardless of their size or weight. That's the facts.

However, each state has their own rules regarding which license is required for heavy vehicles. For example, you as a private citizen, could go buy the largest diesel motor coach available, with air brakes, and be perfectly legal to drive it on your regular non-CDL drivers license in most states. I'm not saying its a good idea, but its not illegal. Some states require a special license if the vehicle exceeds a certain width, length or weight but that's mostly Chinafornia and New Jersey, but there may be others.

You put a company name on it and haul even one passenger or package for a fee, drive it across a state line, and then you are 100% subject to all federal and state laws governing commercial motor carriers.

In Georgia, a CDL is required only if the vehicle is used for commerce, and the GVWR (its rated max weight, not how much it actually weighs) of the truck or a truck-trailer combo exceeds 26,000 pounds. That's why many trucks have a tag that says 26,000 LBS on it. It might be rated for 40,000 pounds, but it's tagged for 26,000 so the driver doesn't need a CDL. And that is true even if it has air brakes. Just don't let them catch you grossing over 26K!

Another example would be a guy that uses his "personal" F350 dually to pull a trailer with lawn equipment around for doing lawn work. The truck has a GVWR of 16,500 pounds and the trailer has a GVWR of 10,000 pounds. The combo exceeds 26,000 pounds and he's using the truck for commerce. He must have a CDL and a DOT medical card to legally drive that truck while he's using it for business. When he uses the same truck to pull his 10,000 pound boat to the lake on the weekend, provided he has no commercial markings on the truck and it is registered to him personally, his wife with a regular, non-CDL license is perfectly legal to drive it.

I can own and drive a semi truck around for personal transportation if I want to, with no requirement to have a CDL, so long as it is for personal use only. That's the law. That's why you see big rigs that are labeled "not for hire." Those are personally owned rigs and not used for or engaged in commerce. Again, I'm not saying you shouldn't be trained and capable, I'm just saying that in most states a CDL isn't required for non-commercial trucks. Your mileage may vary and you might live in one of the states that have different rules, so talk to your local enforcement officers and get a copy of your state laws to read for yourself. Half the time the enforcement officers don't understand the laws either.

 

[Farmallmilitary]

I am rigourously studying all the paper work for the airbrakes and i am getting a much better understanding of the operation. I am almost certain it is a diaphragm I just need to get under it and figure out which one. Also "Artisan" i appreciate the input you have given, so please keep posting.

 

[73m819]

Can I suggest that you install a quick disconnect at the air tank to plug in SHOP AIR, this way you have a air supply without listening to the motor and will you find the leak eaiser

 

[Farmallmilitary]

I will try that when iam diagnosing the place where it is leaking, i didnt think of that. Anyone know where to get a whole new chamber for the 5 ton rockwells? If the diaphragm is bad i dont want to try to rebuild it, that would be suicide. Or should i just take the chamber off and take it to a big rig shop for them to rebuild. I know many places dont like to rebuild them due to the danger of the spring, so that may not be an option.

 

[rangereter]

I think that those chambers are 1216's meaning that on your maxi's (cans with 2 diaphrams) your service diaphram is a #12 and the emergency/parking side is a #16....the single cans on rear and steer axle are just #12 service diaphrams..pretty straight forward to change and just a few bucks apiece at any truck parts store. The park side of the rear cans are #16's and as I said in my previous post, don't service without a full understanding of the assembly. For now just diag your air loss/ brake drag and we will help from there. (don't forget about the chock-block safety glasses stuff either. Regards,
Bob

 

[quickfarms]

We rebuild the single cans all the time but we replace the maxi's (spring brake cans) because the spring is dangerous and the rebuild kit is almost the cost of the replacement. I would suggest that you take the bad can to a truck parts house so they can march it up there are several sizes and different style plungers

 

[juanprado]

Missouri uses the same code as Louisiana and many states. It is not the personal or commercial use. It is the gvwr that drives the requirement.

Below is a copy and paste from the book downloaded straight from Mo. I have also attached it for reference.

You must have a CDL to operate:
 Any single vehicle with a gross vehicle weight rating
(GVWR) of 26,001 pounds or more.
 A trailer with a GVWR of more than 10,000 pounds
if the gross combination weight rating (GCWR) is
26,001 pounds or more.
 A vehicle designed to transport 16 or more
passengers (including the driver).
 Any size vehicle that is used to transport
hazardous materials as defined in 42 CFR 383.5.
Federal regulations through the Department of
Homeland Security require a background check
and fingerprinting for the Hazardous Materials
endorsement. Contact your local department of
driver licensing for more information.

 

[Artisan]

Can I suggest that you install a quick disconnect at the air tank to plug in SHOP AIR, this way you have a air supply without listening to the motor and will you find the leak eaiser

GAWD I hate being a noob! How elegantly simplistic! THANK U.
I have no issues but that is a good tip to remember!

Farmall this trick would be the first thing I would do...GAWD that could
make it so easier to find leaks. I might throw on a valve so I could
pressurize it and throw the valve off.

Farmall have you checked to make sure the ball valves at the 4 corners
on the glad hands are all shut OFF?

( I am learnin' W/ya Farmall! )

( I was eyeballing an M925A1 recently and a pro here told me I needed at least
a Class "B" w/ Air brake to legally operate the M925***. So what did I do? I went and
got it, I asked for an accellerated course at Dootson and they abligsed, with a
grin, for I now understand that a LOT of guys and gals spend THOUSANDS of dollars
to get educated by an acredited CDL school. One chick who was sent to learn w/ me
told me she had spent over $4k so far! I saw others there for HOURS on end and still
having a hard time parallell parking a 36' BUS! LOL! It is not so tough if you
LISTEN to the instructor. So I studied for the written by way of taking the practice
tests they gave me for my state and we cut off the awnsers and made my own
tests, I took the tests over and over and the wife would grade me, THEN I went
back and re-studied everything I got wrong till it was second nature. I passed
everything first time and I got TANK, PASSENGER, CDL B, AIR, MOTORCYCLE,
GENERAL KNOWLEDGE and I think there was somthing else... ( I was told that the
DMV examiners LOVE the students who go to truck driving school because
they teach you stuff the RIGHT way, and not the way your "buddy" teaches you,
FWIW ) Then the actual driving test w/ an examiner, it was like 40 Minutes of
DON'T EFFF UP BRO! NOT ONE MISTAKE. Well, at the very end he said I took
one corner a little fast (NOT) and he deducted 3 points. I think they have a 40
point deal they use. I bet that examiner has NEVER given anyone a 100% pass.
I was PERFECT on every sign, every RR track, pedestrians, lane changes EVERYTHUNG
but no, he said I was a little fast on a corner...NOT! Ha!

So this is all brand new to me too. I am taking it one step at a time and conquering
it. I am well on my way now, but I see years of study before I can fix almost anything
on the behemoth! )

***It is exactly the same as an M923 except I have a winch.

 

[Farmallmilitary]

Ok so as you guys suggested, i hooked up a quick disconnect air coupling to the truck. I then air up the beast (after blocking the wheels) and had a buddy of mine push the brakes while i listened around and crawled around the truck. I found 1 very obvious leak in a airline on the front left tire but it wasnt the MAIN leak. So listening around the rear end I could here air coming from the brake drum on 3 of the 4 rear wheels. I am guessing there is a punctured diaphragm in those pods on the service side of the chamber. So unfortunatly I think i should at least get 3 new chambers but i will probably end up getting 4 chambers for the whole rear end. This is probably another stuipid question but why are there two pods for each brake on the rear two axles? There is a small one just like the ones on front of the truck and then there are bigger pods on the same brake as well. I am guessing it is the larger pod because that was the one i heard actuating.