Air Pressure Issue

kdaniels

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I've done some searching on the forum but haven't found anything ...My M923A2 (with CTIS) will build air pressure on start up to 120psi on both primary and secondary tanks in about 3-4 minutes. BUT when I drive to down the road and use that PSI there is no rebuilding it in the tanks.....as I use the brakes it continues to drop well below safe levels.

If I let it sit for a while (over night) the next morning it will build right back to 120 psi. I'm thinking the governor is the problem. Anyone had a similar issue or can direct me to a solution?


Semper Fi !!


Keith
 

simp5782

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Is your air dryer purge valve sticking on the bottom side of the dryer once it blows off? It can seem air very quick.

Check both of your tank shut off valves to ensure they are open and the handles have some resistance to them. They can get weak and close themselves while driving.

Open the line that goes into the rear of the wet tank and put a few drops of marvel mystery oil in to lube up the three 1 way check valves in the system.

Checking the governor is easy. There is a small line coming down from the frame rail on the passengers side of your air dryer. It is a 9/16 or 1/2" wrench. Take that line off. That comes from your governor. Take it off and drive it and see what your results are.
 

kdaniels

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Location
Dothan, Al
I have noticed no leaks from the system. Tires are all up as they should be, but my air dyer doesn't make the bleed off noise it use to. I have to admit I haven't serviced as I should have and my Monday start up and run days aren't much help in keeping the vehicle serviceable. It made a very loud "goose honking" noise when I first got the truck back in 2013 when I had it idling....it no longer does that...so I'm wondering if the air dyer is (could be a issue) as well.

The governor was my first thought with the failure to rebuild pressure.

Semper Fi

keith
 

sandcobra164

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I had something similar happen. It turned out to be some kind of gunk in the line from the air drier to the governor. There is a fitting midway just forward of the transfer case. What was happening in my case is once the governor signaled the drier to open, it would hold the purge valve open and drain the tanks. Just like you, if I let the truck sit for a while, it would build pressure and repeat the process. In your case, I'd verify the line from the governor to the top of the compressor is clean and able to pass air both ways. I'd look for a plugged line going to your air drier as well since you no longer hear it blow off. I got a newer style drier from member Suprman on here for less than I could get one from a heavy truck place. I'm not sure if he still has them but it's worth looking into. It installs the same, just have to re-drill the bracket as the new unit uses 3 bolts in a triangular pattern and 1 brass fitting has to be transferred from your old drier to the new one if you decide to go that route.
 

kdaniels

Member
192
11
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Location
Dothan, Al
003.jpg It's in pretty good shape...a Air Force truck out of Oklahoma. I drove it the 300+ miles home from Red Stone (Huntsville, Al) back in May of 2013.
 

doghead

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Have you ever serviced the air drier?

iirc, they need it every 6 months.
 

kdaniels

Member
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Dothan, Al
I'm ashamed to say ..no. No excuse. I've got too involved in a few other "olive drab" projects and this one has been put on the back burner. I've been reading the forum on that subject and have printed off the service pages from my dvd manual.



Semper Fi


keith
 

kdaniels

Member
192
11
18
Location
Dothan, Al
On closer inspection while the vehicle was running I found that I had a constant flow of air out of the bottom of the air dryer. I've looked thru some of the posts related to the air dyer and made the determination to replace it with a newer updated unit rather than worry with this one. I do/will miss the explosive air release on the old unit, it was always good for a few smiles from unsuspecting bystanders.


SEMPER FI !


keith
 
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