M1078 airline junction leak - what is it?

[jpelc]

I have 1998 M1078 A0 that Im working on to get ready for off-grid camper project.... discovered air leak from this junction (see photos). I wonder if any one can ID what this line is and where is it going to. It is draining my air while parked.
This is a view from under, looking over the front driveshaft up to the driver side inside chassis rail.

 

[jpelc]

I got the schematic, but no clear to me where is that junction and that line.

 

[Ronmar]

well if it is draining all your air while parked you have some other issues as well. That is the point where air from the front red/emer gladhand via a check valve, charges the wet tank and the rest of the system. it is located in the air sample line that the governor uses to monitor wet tank pressure to cycle the compressor on and off.

if it is leaking it will drain the wet tank of air. There are a pair of check valves between the wet tank and the primary and secondary brake tanks(on the inboard end of the tanks). if the brake tanks are also losing pressure, those tank input checks are leaking air back to the wet tank or air is leaking out of the system someplace else...

 

[GeneralDisorder]

Huh. Completely deleted at some point. My A1R doesn't even have that bracket.

 

[jpelc]

well if it is draining all your air while parked you have some other issues as well. That is the point where air from the front red/emer gladhand via a check valve, charges the wet tank and the rest of the system. it is located in the air sample line that the governor uses to monitor wet tank pressure to cycle the compressor on and off.

if it is leaking it will drain the wet tank of air. There are a pair of check valves between the wet tank and the primary and secondary brake tanks(on the inboard end of the tanks). if the brake tanks are also losing pressure, those tank input checks or something else is leaking air back to the wet tank or out of the system...

Thanks Rommar. I can fix this leak, but sounds like I have more issues. Most likely bad check valves. Already replace one on the glad hand. How would you go about diagnosing it? Just replace all the check valves?

 

[GeneralDisorder]

Replace every check valve. Not worth even taking them apart to inspect. Cheap Haldex COTS parts.

 

[Ronmar]

the test is to fully charge the system(dryer purges) then shutdown. drain all the air out of the wet tank and close the drain valve. Look for pressure drop on the pri/sec-rear/front air gauges in the dash. if you note air loss on the gauge, open the wet tank drain and if it has built up air, it is coming from the check on the tank that lost air pressure. if there is no pressure buildup in the wet tank, then the air is going somewhere else in the system after the service tanks.

Follow the line out of the wet tank to the service tanks, there is a check on each service tank input. disconnect the hose or hoses from the fitting on the check input port, and using 2 wrenches unscrew the inlet side of the check. it is sealed with an o-ring and has a metal star disc with rubber seal and a spring inside.

look for debris and corrosion inside and clean or replace as necessary. Old rubber, the valve probably just needs to be replaced like General said. They are not expensive...

surprisingly the only one i have found bad on my 98 so far is the one up near the front gladhand(pitted to hell), and that was when i was deleting it anyway. every other one i have pulled apart on my truck has been very clean and serviceable...

When clean put a little silicone GREASE on the cap O-ring, re-assemble the spring, disc and cap and re-attach the hose or hoses... Pressurize and leak check...

Just found one of these service input checks leaking on mine a few weeks ago. The person who assembled it used too much thread sealant on the NPT hose fitting and the buildup of gummy sealant had slowly migrated out onto the sealing surface to interfere with the sealing disc. cleaned right up and seals great now...

being an A0 your wet tank is probably plumbed incorrectly. 2 minute fix while you are under there, I can attach some pics when I get home this evening...

 

[Ronmar]

The wet tank is supposed to act as a final filter/dryer stage in the air system before the air feeds into the service brake tanks. Every A0 I have come across has had an issue with the wet tank plumbing, with the wet tank Td off of the dryer output line and fed on to the service tanks. Plumbed like that, only a small portion of the air consumed by the brakes ever sees the inside of the wet tank. You can fix this by swapping 2 hoses on the wet tank so 100% of the brake air from the dryer passes thru the wet tank. Simple fix. One of the lines y0u move is from that fitting in your first pic…

you can also see the primary/rear tank input check valve in these pics…

Before:




After:

 

[jpelc]

General/Rommar, than you for great direction. The line switch makes total sense. Now I understand why they call it the wet tank too! was my next question. I'll get the check valves. To make sure: KN23080. Right?

 

[jpelc]

I replaced the front e-gh earlier this year with this:


It does not appear to be the same as the one on the pri-tank....?

 

[Ronmar]

You want 1/2” thread. Google N13526H

 

[jpelc]

UPDATE: so this was NOT were it was leaking from! I was misslead by tagging on the line as it was causing the sound change. The leak is from farther forward on the bigger line (do not yet know what line it is) thru a pinhole.



Do I need to replace the line, or can I cut it here and join with coupler? This is probebly the most difficult location to work on it!

 

[jpelc]

Also, on the reroute subject: on the wet tank the line to the e-gl is smaller then the once connecting wet tank with the pri-tank. I will need new fittings to make this work. Off hand, do you know what thread goes into the wet tank? I'd replace it with a straight fitting for better direction to the pri-tank.

 

[Ronmar]

Also, on the reroute subject: on the wet tank the line to the e-gl is smaller then the once connecting wet tank with the pri-tank. I will need new fittings to make this work. Off hand, do you know what thread goes into the wet tank? I'd replace it with a straight fitting for better direction to the pri-tank.

The lines are different sizes, but the threaded port where the fittings attach are the same size. I disconnected the lines, swapped the fittings and then re-attached the lines to their original fittings in their new locations. i think those are 1/2"NPT, but would have to measure. Whenin doubt, pull one out and take it along when you get new fittings

My local NAPA stocks DOT air fittings and line. a different angle fitting would probably work better off the wet tank.

For the Pinhole, you could replace the line, or use a compression-compression line fitting in where the pinhole is located. Since it is not the main brake system, I would probably just install a fitting where the pinhole is.

 

[jpelc]

Thanks. I just did that, removed the short line and figure out the fitting swap. NAPA. good advise. as to the pinhole, I think it is a break line or could be CTIS line. It is the same as the 1/2" pri-tank feed line. I need to free them out and trace to varify. It is pressure line and leaks all the time, so my guess it is break line, since CTIS lines are not pressurized (i think) when engine not running). I use shop air for testing, not engine comperessor.

 

[Ronmar]

the only CTIS line that has pressure with truck off is the feed line from the wet tank protection valve, it will only have pressure if the tank is above 85PSI and that line crosses over and runs up the passenger side...

there are 3 lines on the drivers side that would have pressure without your foot on the brake pedal. PRI and SEC air feeding from the tanks up to the pedal and that line running from the front red gladhand to the wet tank via that T fitting you showed in your first post...

 

[jpelc]

Guess I'm replacing that line. Uffff. Life with LMTV.
I'll post an update when done.
Thanks for all the good info.

 

[GeneralDisorder]

Don't need to replace the line for a pinhole. Just get a push to connect coupler, cut the 1/4" out with the pinhole and jam it back together. 5 minutes if that.

DOT plastic air line and PTC fittings are brilliant. They started using them on the A1R and it makes servicing so much easier.