Troubleshooting an air leak

[Geom]

Hey guys,

I've been trying to troubleshoot an air leak in the bus that just materialized suddenly.

A bit of background:

We've been parked here for about a month or so.
To maintain level, we've been using the bus' automatic leveling system.
To keep the air bags full I have an electric compressor hooked into the main air tank.

That has worked pretty well for us so far and the compressor comes on once or twice a day to keep the bags at about 110 psi.

Anyway, sometime today we were just sitting in the bus when I could hear a hiss from outside, towards the back of the bus. There was no pop or any sudden release of air, just a pronounced and steady hiss.

I went outside to look and it sounded like it's coming just forward of the rear wheels, in the middle, and if I had to guess it was on louder passenger side.

I checked to make sure the tank in that general area wasn't somehow open and I poked around in there as much as I could comfortably manage but I could not find it.

The leak is enough to remove pressure entirely from the lines. As where it had been a steady 110, it's now at or near 0.

Thinking it might be the leveling valves getting stuck, I tried to rock the bus back and forth to see if that would unstick them (maybe not something one does, but all I could come up with, lol). Anyway, that obviously had no effect.
Then I got to looking at the book and if I'm reading the air diagram right, the air bag system (including the valves) is a "separate" branch unto itself within the whole air system. The bags are still full and holding the bus nice and level. So I don't suspect a leak in the bags or the suspension system.

After draining all the tanks with what little air was left, I turned the compressor back on. The leak was still there, but I used what little pressure it had managed to build up to pump the brakes a couple of times. I could hear the front brakes actuating.
That also appears to have had no effect.

Any advice on where to look?
It just popped suddenly. We weren't moving and had not moved in a while.
I've been draining the air tank maybe once a week or two and there wasn't a whole lot of moisture in them.
I'm going to continue dissecting the book a bit, but I'm not even sure what system to start looking at. I don't have a way to block the bus, yet, and I'm hesitant to crawl under it, especially with an air leak in the mix. The bags are holding fine right now, but that will not last long.

Anyway, as always any help is greatly appreciated.

Thanks
George

[Ed Hackenbruch]

Don't know about your GM but on my MCI that sounds like it might be the rear brake relay valve.

[Oonrahnjay]

     I'd guess (I don't know anything about your particular bus) that the first place to start is to locate the source of the noise.  Usually a leak happens right where the noise is (like a hole rubbed in an air line) but sometimes the location will tell you something else (if the leak is diffuse and coming from a quick-release valve, look at the place that that valve controls -- i.e. if it's a quick release for the rear brakes, look for a leak in a brake canister assembly).
    Also, the source of the noise will point you towards the possible issue.  Do you have an air dryer and does that air dryer work in line with air from an external compressor?  Since you've been using the air suspension mostly lately, it is likely that will be where you find the problem but you can never be sure until you do the detailed work.
    A 4-foot piece of small stiff hose (I use 1/4" DOT line) and a spray bottle with bubble soap in it are your best friends at this stage.  But be careful of the suspension doing things you might not expect it to do (like moving when it shouldn't) -- use GREAT CAUTION if you have to get under it.

[bevans6]

When that exact same thing happened to my bus (MCI) it was the 85 psi pressure regulator for the DD3 parking brake control.  Just a little square valve mounted on the front wall of the axle bay. 

Brian

[MightyThor]

Had a very similar sounding leak on my 4501 and it was the  front air leveling valve.  It was an original bendix unit and the air was leaking from the seal around the shaft to the actuating arm.  Moving the bus had no effect because the seal leaked no mater what position the arm was in.  The bags could be full or empty and the air flow was always the same, a small his under the front of the bus. 

[Ed Hackenbruch]

But he said it was at the back of the bus, not at the front.

[Geom]

Hey guys, thanks all for the replies and things to look for. At first I suspected the rear relay value since it's in roughly the spot the sound was coming from.

Anyway, I finally 'nutted up' and got underneath the bus. I used some of the stackable rv leveling blocks we had and stacked them under the engine cradle front mount. Not exactly perfect, but good enough.

Armed with my spray bottle of soapy water I proceeded to hose everything down that I could, to figure it out. After some random spraying that accomplished nothing, and after developing more confidence (or is it stupidity? I don't know the line is so vague ) I crawled further under there.
It became abundantly obvious, no spray bottle needed, lol.
One of the brake lines had a pretty significant slit in it. It's (one of) the line that runs from the passenger side dd3 to the reversing valve. I think it's the "Parking and Emergency port". It actually looks like there's a seam that runs the full length of that air line. The leak is in a split along that seam.

I tried a little bit of 'George Engineering' to see if I could get it sealed enough to get it to a diesel shop (long shot I know, but 'George Engineering' has occasionally worked in the past so I figured WTH. I wrapped the line up in some heavy duty pipe tape (fancy duct tape basically) and <shock> it didn't work, lol! It worked for a bit, but considering the pressures that line is under it's not too surprising my little rigging job didn't hold.

So now I'm kinda stuck. The bus won't hold pressure to make it drivable and I'm not sure I'd drive it in its present condition. So I can't get it anywhere to have it worked on.

But after spending some time staring at it (I've gotten entirely too comfortable being under the bus at this point) it occurred to me that i could actually replace this line, if I have the hose made with the ends on it. It just looks like a neatly threaded connection that I should be able to remove from the dd3 and the reversing valve side, and install the new replacement line.

The question is, now, where or how do I get that line made? Is that something that's a standard issue part that can be bought somewhere? Is that something that has to be made? Is our good friend Luke able to provide me with such a thing?
Any other advice?

Thanks again in advance,
George

[eagle19952]

Napa store, any hose shop...While your there get some hose and ferrels unions...one goes others may be close behind....

[Geom]

Napa store, any hose shop...While your there get some hose and ferrels unions...one goes others may be close behind....

Will the replacement hose come with ends? Or are the ends user replaceable? Or will napa install the ends? Do I remove the hose and take it to them?
Sorry, have not dealt with this before.
There's not a napa close, but there is an orielly. Would they be able to handle it?

[Oonrahnjay]

Will the replacement hose come with ends? Or are the ends user replaceable? Or will napa install the ends? Do I remove the hose and take it to them?
Sorry, have not dealt with this before.    There's not a napa close, but there is an orielly. Would they be able to handle it?   

    There are a couple of places near me that have pre-made hoses; and by that I mean hoses which are rubber and have the woven fabric reinforcement.  This is different from the nylon-like DOT tube which is a solid plastic - no woven fabric.  Hoses connect a component on an axle to a stationary item like a valve on the chassis.  These hoses are in a rack - you can choose from 12" - 14" - 16" - 18" - 24" - 36" etc.  They are "fully made up" - they have one end that's a solid thread fitting and the other is a slipping or swivel fitting so that you can screw the thread into a component.  You buy them for $14 - $18 (or more for the longer ones) and it takes 5 minutes to install one.

    But there's a trick that you should put in your "George Engineering" tool bag.  If you have a small hole or split in an air hose or similar (like a water hose), you can sometimes limp to help by putting on your heavy-duty tape on and them compressing the whole thing with a handful of screw-type hose clamps.  Often if it splits or tears, it will just split or tear somewhere else but - if you're stuck - it's worth a try.  Also, if you have a crack in a hose or pipe near a metal fitting, you can sometime cut the tip off the hose or pipe and get it to connect back into the fitting; obviously, there has to be a little free play for this to work.  And the same applies, if it's in bad enough shape to crack or split somewhere, it's probably going to crack or split somewhere else soon so be sure to do a good repair ASAP.

[bevans6]

Just remove the hose, take it to a truck parts store and ask for a new one.  they will either have a ready made one, or will make you one, or will sell you the hose and the ends and you will make it - it just depends on the size and the ends.  Once you get that hose fixed you get to replace all the hoses back there - been there, done that.  The hoses usually come with one fixed end, and one end that can be "clocked" so that you can tighten it up with with the other end fixed tight.

Brian

[Oonrahnjay]

      Yeah, Brian and I contemporaneously posted.  We're talking about the same thing.

[luvrbus]

Most of the time from the rear relay to the can the hose has reusable nuts with ferrels guess we will see when you remove the hose is so all you need is the length of hose and 2 new ferrels   

[MightyThor]

In order to move the scenicruiser home I had to re-plumb all of the rear brake lines to the tag axle.  The modern DOT air lines are plastic.  I chose to use Synflex tube from Eaton.  I expect to do a lot of reworking of my air system so I acutally bought rolls of tubing in different sizes.  The brake tubing I used was 1/2 inch.  Part of the system was already compression fittings with the compression nuts and compression ferrels.  If you don't know what that is, it is the same kind of system used on most supply lines to ice makers in refrigerators.  you slip a threaded nut onto the tubing, then slip the ferrel which looks like a little brass doughnut and you stick the tubing into the fitting on the brake canister and then slide the nut and ferrel down and tighten them together.  The other system that I have seen is more like the connection for a natural gas line on your appliances.  there is a flare on the pipe that is squeezed against a matching contour on the fitting.  The compression is really easy to do yourself.  The flare usually requires more specialized tools and seems to be less common so may be harder to get parts while out on the road.  Compression fittings are sold at hardware stores, auto parts stores, and truck repair centers.  Flare fittings are also sold in similar spots, but the flare ends on the hoses may have to be made by a place with the flare tools.

[Dave5Cs]

George, You might be by another busnut that can help if we knew where you are close to.
Also any Parker hose and hydraulics stores around or ask at O Reilly's if any Hydraulic stores or shops around. Camping Worlds, Truck shops.

Also when you get home get Coachnet 129.00 a year is worth it.
Dave