Air leak on M925A2 , Air dryer line?

[bulldog_mack13]

I have an air leak coming from a valve? on the rear of my wet tank behind the big tool box. I circled the part that's leaking air from the top and from a small port on the side. Its an issue when the truck is shut down, it will leak its air out in about 15 or so min. Also this might be related but I have a bit of water in my air tanks time to time.

I replaced the part with one off a working truck and it still leaks, I know its not that.. I think. Pic one is the underlined line going from the part leaking to the air dryer, pic twois the part leaking from the top and from the port on the side, and 3 the underlined line going from the part to the air dryer.

The air dryer sounds like it should and lets off at 120. Could this be fixed by a new air dryer filter or new air dryer? Any help would be appreciated a lot so I don't spend a lot of money on parts I don't need. Also the air flows from the air dryer to the tank via this line and not the other way around correct?

I also am going to order a new engine air filter.

 

[bulldog_mack13]

Any ideas?

 

[Suprman]

In the second pic it looks like the 150psi safety valve. They go bad. You can get a kit with the haldex cartridge and a replacement safety valve. Do both air guages go to around 125psi or do they go higher say 150-160.
Will

 

[bulldog_mack13]

Will ,
They go to 120 then you hear the air dryer. I pulled that valve set up off another truck that was working correctly. I will pull off the valve and go to NAPA and ask for another new one if you think that's the route to take. Thank you

 

[Suprman]

Napa won't have it they have one that's around 160psi it's a smaller size I had to go to the plumbing supply store and make an adapter. The air dryer has an expello valve in the center. It vents out moisture the air dryer collects. It should not vent every time you hit 120psi though. They are known to get leaky, sometimes if you take it apart and clean the parts then put it back together that will cure it. If its a constant leak you can us some windex to find exactly where it is leaking from.

 

[bulldog_mack13]

Its coming from the valve I circled in the picture out the top of it and the tiny port hole on the side of the valve .

 

[Suprman]

That is a safety valve. If pressure gets too high it will vent it before something bursts. You want to get one that is set to 150psi to replace it with. Take a brighter daytime pic of the whole air dryer.
Will

 

[bulldog_mack13]

Will ,
I pulled the filter on the dryer, its pretty nasty but the dryer works like it should. I had to order a filter at 160.00. I also ordered a new safety valve for 150 psi.
I replaced that valve already with one from a truck that didn't have an issue and it still leaks. So with my 100% new one I hope this fixes it.

 

[Suprman]

The valve shouldnt leak unless you are over pressure. There are check valves that can get sticky and restrict air flow if the replacement 150psi valve is opening then you may have another problem. They are hard to get the valves off so if you used a wrench and it got a little bent taking it off the good truck then that can cause a leak.
Will

 

[juanprado]

If I read your post correctly, The valve that is leaking is next to the wet tank in a "t" fitting circled in red?

It is a high pressure relief valve. The abs training handout on the m939 conversion shows it to be a 250 psi valve. pg 11 references it going to the dryer.

http://igor.chudov.com/manuals/M939-Series-Trucks/ABS-Maintenance.pdf

I searched the 3 part tm's from Sept 2012 but could not find it. I will also not claim to be a tm expert. More seasoned hands might find the correct listing.

All the brake parts are made by midland/haldex. Normally they have part or casting numbers. If you can pull the part or see if it has a reference and post it, I can check my part references as I did it for 20 years in another lifetime......

 

[bulldog_mack13]

Juan , Will ,
I replaced the air check valve, and the 150 psi air relief valve. Cleaned everything and also put on new fittings. Pretty much everything that screws onto the wet tank from the air dryer is new.
I am changing my air dryer filter and using the kit that it came with to replace the things inside.

Now Juan , you say I should be a 250 psi and not a 150 psi relief valve? If so I can get one ,

 

[juanprado]

I think there are 2 high pressure relief valves. A 150 on the bottom of the drier and a 250 in line by the wet tank.

Is the one next to the wet tank leaking?

 

[bulldog_mack13]

Yes the one the I circled is leaking form the top and the small side hole. That is the one that is next to the wet tank. I replaced all that today but I cant check it until I get my air dryer back up to shape.

 

[juanprado]

Not a bad idea to have also changed the one way check valve as some members have reported it to be rusted up from not draining the water in the tanks.

hopefully it is just the relief valve and not a by product of another problem.

Keep us posted.

Where did you find the large relief valve? Do you have a part number?

 

[bulldog_mack13]

I got it from the Kenworth dealer. But im sure any auto parts or truck parts place has them. Its a Bendix pop off valve part. 284142BXW is the number on my invoice from them. $ 19.13

My one way Bindix check valve looks backwards from the Midland one that I had off another truck but I installed it like it came off. I will know something soon I hope after I get my dryer done. I hope this really fixes my issue.

 

[juanprado]

Bendix 284142 part number ST-3 safety valve looks to be correct and an exact replacement. I checked the bendix, meritor, and haldex catalog and there is no listings for 250 psi except one specific "special" model used on a "el" compressor. Most valves show to be in the 150 psi range. The meritor and haldex similar function relief valves are shaped different but are functionally the same.

I think the training hand out is not correct on the 250 listed. I would disregard that info.

 

[Suprman]

My air dryer safety valve was leaky on the first 5ton I bought and the only local replacement was a 175psi valve. I was driving around a few days after replacing it and looked down at my air pressure gauges and they were both at 0. It took me a second to figure out the ppv had seized closed the gauges were pegged and the valve was venting at 175.

 

[bulldog_mack13]

Here's what I did.
I replaced the air check valve , and 150 psi air safety valve, all the fittings and such for them from the air dryer line to the wet tank. About 60 dollars worth of items. Then I bought the rebuild kit from a place in town for the air dryer and got a new outer filter for it. $138.99. I rebuilt all that today and cleaned it all. I cranked the truck and I don't hear or see any leaks. Knock on wood. So I cant say exactly what fixed it but that's what I did.
Now to fix my trans temp gauge?

 

[Suprman]

I don't know anything about the trans temp gauge but glad to hear the air leak is fixed.

 

[bulldog_mack13]

One more air question, on a yellow air line under the dash behind my PTO/Winch controls I have this ??" in line air filter" ? ? I think that's what it is, its leaking from the bottom where it looks like some threads for a cap once was?. Is this something my truck needs or should I just connect the line where it was or should I replace it? It looks pretty old. Thanks troopers .


P.S. I feel im getting close to having the truck done. Knock on wood I don't have any water in my air tanks anymore.