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M35A3 (M109A4) disappearing air pressure

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Location
Dover, New Hampshire
Hey all, new M109A4 owner here. I'd like to share a problem I am having with you guys in hopes that I can track down the issue. My air pressure builds normally and pressurizes the CTIS system just fine. When I go to turn my wheel however, the air gauge drops to zero PSI and the buzzer and warning light come on. Wait about 30 seconds and the gauge jumps right back up to operating pressure. The air assist steering does not seem to be functioning at all and when this happens the transfer case disengages as well (if engaged at the time). My question is this: Is there some sort of overload or leak protection valve that is causing this issue? Seems almost like a circuit breaker for an air system is tripping and cutting off air to the steering, transfer case and gauge. If such a thing exists where can I find it? I'm not sure but there may be an air leak upstream in the air assist steering system that is causing this but if I can't maintain any pressure in the system there is no way to look for it! Help!
 

Elijah95

Certified Rookie
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Georgia
There is no air protection safety valve that I’m aware of on a deuce, what your experiencing is most likely an extremely large loss of air, and when air drops too low you will lose your wipers/horn/CTIS/brake assist/t-case to front axle air shift engagement

The air assist steering on A3 series Deuces (in your case, 109a4) is extremely greedy for air when properly functioning and often times just backing up a trailer rocking the wheel back and forth can drain a system fast! Often times they need to be rebuilt due to leaking seals

So I advise this:
Crank the truck up, build air pressure until it stops building, shut it down, and gently apply pressure to the steering wheel left or right. You should lose air pressure, but it shouldn’t blow the tanks pressure in one big old blast.

Report back with results


Sent from my iPhone using Tapatalk
 
Last edited:

HDN

Well-known member
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Location
Finger Lakes Region, NY
Welcome to the A3 club! In my experience, the air-assisted steering cylinder will suck a lot of air with a lot of back and forth steering movement, like when parking in a tight spot, to the point that my air buzzer will sound. I believe that is normal behavior. My truck is a 1995 and I haven't done anything to the steering cylinder yet.

Have you looked in the support TMs for troubleshooting info? I'd start there.
 

M37M35

Well-known member
Steel Soldiers Supporter
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East Central Oklahoma
My question is this: Is there some sort of overload or leak protection valve that is causing this issue?
There is no air protection safety valve...
Actually, I think the A3s/A4s do have a protection valve to keep the steering or CTIS from completely draining the system if something goes wrong. If I remember right, it shuts off at 60# to maintain air for the brakes. If it's defective, that could be your cause.
I don't know where it would be located, but you could check the TM, or follow the air lines.
 
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HDN

Well-known member
1,937
4,646
113
Location
Finger Lakes Region, NY
Yes, there is a priority valve in A3 air systems to reserve air for brakes. If you haven't found the TMs yet, you can find them on Jatonka's site. I don't think there are A3 TMs on SS yet for some reason.
 
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