m939 air system check valve

[Bolkbich]

My M932a2 was doing funny things. The air compressor was cycling ,the safety blow off valve on top of the air dryer was popping off with only 100-120lbs of air. I started at the dryer and was going through everything when i came across a check valve inbetween the dryer and the first air tank. It was rusted solid and only letting small amounts of air through. I split the valve cleaned out the rust and freed the rubber check. Fixed all my problems. I checked my other 2 m939's that showed no symptoms and they were rusted solid too. One i could free up , the other broke trying to get it apart. They build air much faster now. Just a heads up , if all 3 of mine were stuck im sure its a common problem.

 

[Stonepicker1]

You are correct on those check valves going bad. Back in the late 90's we went through all of our M900 series trucks and and replaced most of them.

I will be replacing all of my check valves on my new M923.

YOU GOT TO DRAIN THOSE AIR TANKS.

 

[usmarines72]

Where can a guy get those check valves?

 

[Stonepicker1]

Where can a guy get those check valves?

Google "N13526H"

 

[Bolkbich]

I checked a couple of other check valves on the upper tanks they were all ok. It just seemed like the first valve had the condensation sitting in it. Im going to check my local truck parts guy tomorrow. Hope he has them. I hate specialty parts.

 

[usmarines72]

How many of these check valves do these trucks have. Might as well order enough to replace them all.

 

[Stonepicker1]

How many of these check valves do these trucks have. Might as well order enough to replace them all.

I think it is three.

 

[wsucougarx]

Bolkbich thanks for the heads up!! Just ordered 4 valves off ebay for $7 each. Also picked up a spare fuel solenoid just in case. Are there any other parts someone should have on hand that are frequent problematic?

 

[srodocker]

Found this thread searching for air problems. Will order some of these check valves! thanks for the ###

 

[M35A2-AZ]

I have a problem with one of my trucks that the dryer popping off every 30 sec.
I was thinking it maybe the regular on the fire.

 

[R Racing]

I replaced mine hoping it would fix my problem. But when I took the old 1 out it was like new inside. replaced the air governor . next im digging in to the unloader valve.

 

[Coffey1]

I think a Q2 quick release valve would be important to keep one in tool box.
It has a nylon ball in that can crack and break.
And when it goes every time you step on brake all air dumps
Never have liked where they are mounted.
Hit it on rock or tree stump and break it your stuck with no air.
.

 

[hklvette]

You are correct on those check valves going bad. Back in the late 90's we went through all of our M900 series trucks and and replaced most of them.

I will be replacing all of my check valves on my new M923.

YOU GOT TO DRAIN THOSE AIR TANKS.

Or you could just keep the air drier serviced. If you're getting water in the tanks on a drier-equipped truck, it needs a new desiccant can at a minimum.

 

[Swamp Donkey]

Google "N13526H"

I'll pass this along as a possible cheaper alternative.

The number above can be crossed to KN23000, which also has better availability, according to a chart I found on Google. My local Truck Pro had them in stock for $12 with no account. You might be able to do even better with an account. Don't waste your time at Napa. They want $29 a pop. I have not checked yet but some of the other valves can possibly be crossed through this chart. Link to the PDF is below.

http://www.google.com/url?sa=t&sour...qmREQKj8CmwS_R1TaGu6dPQ&bvm=bv.81828268,d.cWc

 

[Doug Roberts]

yikes ! yeah I got in and ordered 3 at $10ea , and I'm the guy that drains everyday ( that's what she said )

 

[SLOrazorsedge]

Albert, I just had the same thing occur to my M931A2. It was the ST-3 safety valve. Google Velvac ST-3 safety valve, they are about $15.00 at a truck parts house. I thought it was my air dryer but its this valve inline to the dryer that popped off and blew steadily. Once replaced, back operating perfectly.

 

[M35A2-AZ]

Albert, I just had the same thing occur to my M931A2. It was the ST-3 safety valve. Google Velvac ST-3 safety valve, they are about $15.00 at a truck parts house. I thought it was my air dryer but its this valve inline to the dryer that popped off and blew steadily. Once replaced, back operating perfectly.

It that the one at the end of the wet tank?
Mine is not steady, it pops off every 30 sec. or so.
But I will make sure it is not the ST-3 popping off.

 

[1 Patriot-of-many]

It that the one at the end of the wet tank?
Mine is not steady, it pops off every 30 sec. or so.
But I will make sure it is not the ST-3 popping off.

If it's the safety valve at the end of a tank, you better fix it pronto. Usually the ppv valve is frozen up or rusted.

 

[SLOrazorsedge]

Yes, its inline with the wet tank. My truck's air pressure suddenly ran amok building from 120psi and running up towards 150psi. I immediately pumped the brakes down to 90psi and it began running up again. Being as I was only 2 miles from home, I started that way and pumped the brakes down when they hit 120+. Suddenly there was a huge whoosh noise and air release blowing constantly. My air pressure barely maintained 90 psi until I got home and parked. The ST-3 safety valve was blowing. I removed the ST-3 which appeared brand new, the truck is a NOS total rebuild, new cab, axles, motor, trans & transfer, everything with only 20 hrs and 220 miles. The new valve immediately fixed the issue. The replaced valve simply was full of crude from sitting at Ready Reserve and DRMO/GL.

 

[lindsey97]

Would you guys be kind enough to take a picture of the location of those check valves?

I found the pressure protection valve, bendix PR-2.

My truck is a 1990 m923a1. I am experiencing an overpressure condition much like SLOrazorsedge. The truck functioned perfectly until we had a our first freeze of the year.

I changed the haldex air dryer filters, part # DQ6036, and that made my wipers, horn and 6x6 engage air switch work again. but the truck still overpressures to approx. 140 psi.

I am considering replacing the air governor, but I suspect that the ppv may be not allowing the governor to function properly. I have read some of wheelspinner's posts using the search function which leads me to the ppv malfunction.