M923A1 Air Problem

[sd39u]

I'll preface this by saying...I'm at deer camp with my M923A1...and 80 miles from my tools and my technical manuals with really bad cell reception so trying to view them on an iPhone in 3G coverage ain't gonna work.

Air pressure won't build past 60psi, low air light stays on. Checked all the usual easy stuff, looked for open valves etc.

Any easy suggestions before I park the truck at deer camp and have my wife come pick me up?

Thanks!

 

[74M35A2]

60psi is the minimum for brake operation, it may be OK to drive carefully?

If it builds pressure at its normal rate up to 60psi, then something on the accessory air side could likely be causing the large leak. There is a PPV (pressure protection valve) that insures the primary brake tank(s) get at least 60psi before other non-essentials get their air. Items after the PPV are things like wipers, horn, and at least one other I am forgetting.

Do you hear air escaping if you then shut it down and listen to where it is coming from? Check all 4 glad hands, and the blow hole at the bottom of the air dryer to make sure nothing is escaping there. Same with the tank drain valves. Air escaping from the wiper valves/motors or horn? Any air hissing around the compressor governor which is on the bulkhead just above the horn?

 

[Coffey1]

Also check valves on tanks to see if they are open.
You never know a tree branch could have close it.
Very remote but I like to look at all possible causes

 

[sd39u]

It builds air very slowly...i heard a slight leak like it was coming from spring brake valve...cycled that and it went away. Air still isn't building.

 

[infidel got me]

I just fixed my buddies truck last week, wouldn't build air past 60 psi. It was a bad diaphragm in the rear brake can. The leak was loud enough to find easily. Hope you find it, bag a 12 pointer.

 

[Suprman]

Sticky unloader in the air compressor head is a good possibility. Check under the air dryer see if the expello valve is leaking. Could be related to the governor but every time I have an air issue its usually one of the first two.

 

[sd39u]

Just oily stuff that came out of air dryer...the valve was closed. Gonna find a rock and tap on the top of the compressor.

 

[Csm Davis]

Okay there are two valves onto the wet tank close one and see if you gain air or lose air if needed if you can open the first on then close the other, they control the primary and secondary air systems. One of them closed off should get you home.

 

[JohnnyBM931A2]

60psi is the minimum for brake operation, it may be OK to drive carefully?

If it builds pressure at its normal rate up to 60psi, then something on the accessory air side could likely be causing the large leak. There is a PPV (pressure protection valve) that insures the primary brake tank(s) get at least 60psi before other non-essentials get their air. Items after the PPV are things like wipers, horn, and at least one other I am forgetting.

Do you hear air escaping if you then shut it down and listen to where it is coming from? Check all 4 glad hands, and the blow hole at the bottom of the air dryer to make sure nothing is escaping there. Same with the tank drain valves. Air escaping from the wiper valves/motors or horn? Any air hissing around the compressor governor which is on the bulkhead just above the horn?

The one you forgot might have been the CTIS system, though he doesn't have that on his A1.

 

[Artisan]

#1 Call a pro for advice.

But...

Let it build as high as it will go then shut it off.
JUMP under the truck and listen for a leak
at the rears.

See if you can ID an air leak at one wheel.

If you find a leak at one wheel cap off that air line
to it and cage that one wheel. Vise grips?

I do not see why this would not work.

See #1

I do not know diddy but what I do is I have an IPAD and
I have loaded all the TM's on it. THAT can save you.
Food for thought.

 

[lindsey97]

Faulty air governor or unloader is malfunctioning on top of the compressor.

Does it build air evenly into the primary and secondary, or just primary? Do your wipers, 6x6, and horn work? If not then the ppv has rust and trash in it preventing the secondary from building air.

 

[lindsey97]

Turn the adjustment screw on the air governor one turn each direction, then back to where it was, maybe it will work again. Drain your air tanks also. Is it freezing where the truck is located?

 

[sd39u]

It was 27 degrees yesterday morning. I'll turn the governor each way.

No wipers, no horn. I drained the tanks during the day yesterday. I've got an air compressor hear at the barn and some basic tools.

Thanks again to all for the help so far. Those TM's will be on my iPad as soon as I get home!!!

 

[Suprman]

The ppv wont open unless you have around 65psi. The governor is past the ppv so if you have no horn and wipers adjusting the governor is pointless. I have seen air dryer filters totally clogged up. Sometimes you can unscrew the top cartridge and pull out the small tube filter part and put the main one back on and it will work ok temporarily.

 

[sd39u]

Got it! Valve on the back of the air dryer stuck open. Piece of red gasket stuck in it. Popped back in and the air came up. had to crawl under while truck was running to find it.

Thanks again folks!

 

[Scrounger]

That is good that you found the problem and are able to get the truck home.
I would suggest that one of the first things on the vehicle maintenance list would be to replace the dryer. While one could rebuild the existing dryer there are members on the forum that sell new dryers for less than what it would cost to rebuilt the one you have. And that doesn’t even cover the time involved.

 

[Jeepsinker]

Also, I know you found your problem, but carry a spare brake light switch. They are a two piece design, half plastic, and they blow apart sometimes.

 

[sd39u]

I just checked the classifieds...no air dryers...I'll keep checking.

Truck is home, tech manuals installed on the iPad. No deer!

That is good that you found the problem and are able to get the truck home.
I would suggest that one of the first things on the vehicle maintenance list would be to replace the dryer. While one could rebuild the existing dryer there are members on the forum that sell new dryers for less than what it would cost to rebuilt the one you have. And that doesn’t even cover the time involved.

 

[74M35A2]

Contact Suprman, he has them brand new complete for the price of a replacement cartridge. He is listed in the Vendor section with them. I have bought several things from him, always a positive experience. He authored post #14 above.

 

[Scrounger]

I can concur with the above post. Suprman is a good person to deal with and has a good price on the dryers.