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No air brake engagement on M35A2

502NDMP

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This is a question asked by a friend, and I did try and find info before posting. He states that the compressor is working and he is building air in the air packs but has no air-assist. He didn't find any line leaks, any suggestions what may be happening or where to start looking for a solution. Thanks to everyone in advance.
 

cattlerepairman

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Lack of air assist but brakes working would point to the air pack not doing its job.
It can be rebuilt or replaced. Brakes not working could also be a bad master cylinder.

Especially for people not very familiar with the trucks I recommend downloading, reading and following the Technical Manuals ("TM") which have all the illustrations and step by step instructions you would ever need.

It takes a bit of effort up front to get used to the TM, but it is well worth it.


TM-9-2320-209-20 is the Organizational Maintenance series, so it has a bunch of different volumes that it's listed under.

TM9-2320-209-20-1 is the Maintenance Schedule
-20-2-1 and -20-2-2 are the Org. Maintenance Troubleshooting
-20-3-1, 2, 3, and 4 are the actual Organization Maintenance repair manuals
-20P is the parts manual

You'll probably want to look in both the Troubleshooting manuals and the actual repair manuals. They are all listed on the "Deuce TM's" page on this site or you can go to https://jatonkam35s.com/jatonkaM35sTMdownloadpage.htm
and get them there.

Also, searching on this site will unearth a treasure of information.



Sent from my SM-G950W using Tapatalk
 

502NDMP

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Thank you for your in-depth reply! I used to have a quad cab and all the TMs, but sold a couple of years ago. I thought it may have been the air pack, but was puzzled that it was building air, etc and they were not working. I knew someone here would have a lot more experience than I with these trucks. I am on the CUCV learning curve myself after downgrading. Thanks again for taking the time to help out.
 

cattlerepairman

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m715mike opens another can of woms - and we do not know because we do not know your friend and how much clue he has when it comes to brake systems or the M35. The brakes could be far out of adjustment and simply not generate enough friction to brake well. The linings could be contaminated. The hydraulic system could be low on brake fluid (we do not know if your friend knows where the master cylinder is and how to check brake fluid levels) or in need of being bled.

So - any "advice" is based on assumptions, the most obvious one is that the situation is as it was stated - everything works but there is no air assist.

The 24 series TM (troubleshooting) says the following (I use the 361 series manuals from 2006 because I like those):
 

Attachments

502NDMP

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I’m curious (and this may be a dumb question), but what are the symptoms (what is the truck doing / not doing) that leads your friend to conclude that there is no air assist?
He says that he feels that only the manual aspect is functioning when he brakes, basically almost both feet. He drove trucks in the USMC, so I am assuming he knows the difference. He doesn't have internet, so I am trying to help him out. Sorry I only have limited information. The master cylinder was replaced and the brakes were done by me before I gave him the truck, he checked the master and it was full and we did use the proper fluid. I will print and forward the attachment for him and have him go through the air pack system. Thanks again for all the help
 

fasttruck

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A sign that the hydrovac is working would be to listen for air exhausting from it when the brakes are released. It has to be quiet to hear this. Build air pressure, shut engine off, operate brake pedal and listen.
 

502NDMP

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No sound or air release noise, completely quiet. So, the hydovac is not working.
 

cattlerepairman

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Now your friend needs to decide if he wants to spend $90 and a half day or $500 and an hour. Rebuild kit and doing the overhaul vs. installing new air pack.
Tactical Repair on YouTube has two real-time videos on how to do the rebuild. Other than a bit of time it is really not that bad.


 
Last edited:

cattlerepairman

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If it was my truck I would probably do two things before I rip the airpack out:

- drain all air pressure, remove the splash shield and add air tool oil to the big chamber; in the usually recommended location (small 1/8 hex plug; see black arrow in this thread: https://www.steelsoldiers.com/threads/where-to-put-oil-on-air-pack.87592/#lg=post-1123810&slide=0). If you cannot budge the plug, simply remove the lower end of the J-pipe and add oil through that hole).

- I would also drain all air pressure , remove the air line at the very top and add air tool oil into the pack there. After re-connecting everything I would gently and persistently tap the middle part of the air pack with a hammer. That is where the compensator piston resides. If it is stuck, nada happens.

Then refill air reservoirs, and while soldier B operates the brake pedal I would continue tapping.

Will it free up whatever may be stuck? Perhaps. If it does, the added lubrication might just do the trick and keep the pack working.

Nothing ventured, nothing gained.
 

502NDMP

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Wow, thanks for all that information. I am going to print everything up for him and drop it off. Thank you to everyone for all the information and suggestions. He is going to have plenty of things to check, he is pretty bored with all the time off, should be fun for him. He is going the rebuild route, but I wanted to rebuild the air pack...he is not the only one who is bored stiff, looks pretty straight forward.
 
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