Air bleeds off way to quick

[dj]

Ok here I am again...I have a 1988 MCI 102A3 and the air pressure bleeds down to 50psi within 10 minutes then down to nothing with in a half hour....And is excessively slow to air up.  Ive done the soapy water trick fixed a bunch of leaks, changed the drive axel air bags (bad) still want to change all air bags out and keep the good used ones for spares. But can't find out why the air is bleeding down so quick....any ideas on where to look will be GREATLY appreciated...Thanks Doug

[Tony LEE]

Air bleeding back through leaking valves in the compressor and other non-return valves is pretty hard to pin down. Air beam leaks in surfaces you can't get at. Belt tensioner air bleeds.

[brmax]

Good morning (coffee in hand here)
Can you see and have access under the bus when no air is in the system. If we can recall when some of this happens or starts is a real benefit. Examples are when wheels are blocked from movement, does the system build completely.

Another good example is; when parking brake is applied and or released does this system still leak. We can help with some past issues with lotsa searching sometimes but if we can nail it down a bit closer can sure help ya.

Floyd

[richard5933]

There are many more places that have air lines than I would have thought about when I started with a bus, and each and every one of them is a potential leak. I've got a set of flare nut wrenches handy to check tightness every time I find a new connection somewhere that I'd missed.

I know that we've got different buses, but here are some of the connections I've checked and found leaks at many: brake release knob(s), windshield wiper system, windshield washer system, plumbing going to all the air tanks (including to the petcocks), brake treadle, air throttle (both ends), lines running to the leveling valves, the leveling valves themselves, the lines to the air bags, lines to your brake cans, etc. etc. Death by a thousand paper cuts...

However, given your symptoms it does seem like you've got a bigger problem somewhere. You've got air leaving the system pretty quick after shutdown, and combined with the slow air up I'd wonder if a check valve or compressor problem isn't the cause. Or perhaps you've missed a larger leak somewhere that you can't access or see?

[chessie4905]

If you know where the air source comes from for the leveling system, you can temporarily disconnect line and plug source. Then see how fast air bleeds off. Then you can work on remaining system, brakes, accessories, etc. first if it is still leaking off fairly quickly.
Also dont forget to check all low presure warning switches for leaking. Use of a mechanics stethoscope is invaluable. Use it without the metal probe attached. Soapy solution is best for small leaks, but messy. Find and fix the noticeable leaks first. Expect leaks at air system components first. Lines and connections second.

here is an example. remove end assy and use hose or tubing end for air leaks.
https://www.ebay.com/itm/Auto-Mechanics-Stethoscope-Car-Engine-Block-Diagnostic-Automotive-Hearing-Tool/152262441892?epid=524007515&hash=item23738c7ba4:g:xm4AAOSwmfhX7kA7

[brmax]

There are many great articles or topics that members have shared and some experienced. Here below is just one link that may have a tip or lead that can help in your tracking down this leak.
A priority I like to start with is getting an area ready for all your looking around, and reason I mention wheel blocking, safe access underneath and all that safety stuff.
Link follows: http://www.busconversions.com/bbs/index.php?topic=25279.0

Good day

Floyd

[kyle4501]

When I had a no air building issue, I started replacing parts based on suggestions from 'experts' based on my symptoms. No success. 

Then I decided to start at the compressor. I disconnected it at the air dryer & connected it to an air gauge and a hand valve so I could leave the valve open when I started the coach & then close it to see how fast it built pressure & then open it to prevent over pressurizing the compressor.
The compressor was fine, so I moved my set up to the outlet of the air dryer - NO PRESSURE BUILD. Ended up being a bad blow off valve.
So, a methodical approach was be helpful for me.

Now, I use a remote air compressor (far enough away that I don't hear it) to air up the coach - makes it easier to hear the leaks.
A leak large enough to air down that quickly should be audible . . .

Good luck.

[Taibob]

Doug,

I have been plagued with the same problems.
Sprayed everywhere ,no bubbles, no sound. 
Luvrbus [Cliff] once said "If you cannot see it or hear it,
It may be leaking out a brake unit or leaking back into the compressor".
My air bags are plated off, and brake units are good.
Pulled the hose off from the compressor and it was leaking back.
Ordered a new air valve [located at tank by differential]
Shall install this week and hope my leaks are fixed.
HTH

Bob

[Jim Eh.]

Good idea to wear safety glasses when working on an air system. Always assume the gun is loaded!

[dj]

Hey thanks for all the input,    I used to be a heavy truck mech so I am familiar with air systems ....never thought of air bleeding back into the air compressor ,  just goes to show you can teach an old dawg new tricks.
Ill be checking that this week end Ill keep you all posted might help some one else.   I do know I don't have the "air beam" system so that helps,  I know the wipers leak Ive got those capped off and going with electric conversion soon.   hate getting under that thing sits kinda low with no air and Im not 20 anymore. thanks again for the replies