Author Topic: Air pressure leak on coach  (Read 14324 times)

Al Lewis

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Air pressure leak on coach
« on: February 10, 2016, 05:09:09 PM »
I have a sudden new problem. At a 20 minute rest stop the air pressure went to zero. After starting the engine it built back up quickly. It drove on home normally but the gauge fluctuated between 90 and 120 about every minute. Initial testing tells me that pressure for suspension, service brakes, and park brake stay up and only the gauge drops. What is going on?

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Re: Air pressure leak on coach
« Reply #1 on: February 10, 2016, 08:07:25 PM »
Al,
Sounds like your air system has developed a leak. The reason for the fluctuating gauge is that the compressor is sensing low pressure and turning on to re-build the pressure. You may be able to locate it by listening for air escaping with the engine off. If it is the system the supplies the air brakes, recommend you get it fixed soon as loss of air if the compressor can't keep up can result in the brakes locking up.
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Lee Welbanks

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Re: Air pressure leak on coach
« Reply #2 on: February 10, 2016, 09:17:55 PM »
Al,

This sounds like a pretty good leak, as Steve stated you should be able to hear it. Park the coach on level ground chock the wheels, parking brake off, build up pressure until compressor cuts out and then shut the motor off get out and listen for air leaking from the front or rear. The Maxi parking brake should auto apply around 50 psig. The suspension should stay up as the air is locked in by the system. At the stated leak rate you should be able to hear it, if not its time for the spray bottle and dish soap.

Al Lewis

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Re: Air pressure leak on coach
« Reply #3 on: February 12, 2016, 08:04:45 PM »
More testing after it sat for three or four days. The gauge read zero. The ride height only dropped one half inch, and the brakes would work but I could tell the pressure was low but not zero. I cannot hear a leak. Testing with soap (windex) I find two minor leaks at the tank screw in adapters. This explains the leak down over several days I have had for many years. After running the engine several minutes air pressure on the gauge was 130. Turned the engine off. After 15 minutes the reading was 95. 65 after 45 min. Zero after 75 minutes. But ride height, parking brake,and service brakes seemed to have normal function and sounded like good pressure. Could the gauge be bad? Are there one way check valves in the system? I don't understand the pressure variation while driving if everything except the gauge has good pressure?

Lee Welbanks

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Re: Air pressure leak on coach
« Reply #4 on: February 12, 2016, 08:52:30 PM »
Al,

So what your saying is when the gauge is reading zero but your service brakes still function. Are you able to release your parking brakes, if so you pressure is about 55 or 60 psig.I have no idea why the gauge is zero and you still have air, the gauge is supposed to be connected direct to the air tank. If you still have air in the service side system and the gauge is zero go out and open up your drain valves and see what you get,
The leveling system will hold the air or should even with the service side at zero it is pretty much completely separate for the service side of the air system. This is a weird one, just have to keep hunting.

Keith Moffett

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Re: Air pressure leak on coach
« Reply #5 on: February 12, 2016, 11:04:40 PM »
Al
Just a suggestion.  I have found that Windex isnt soapy enough to do the job on bigger leaks.  Small leaks bubble up slowly so Windex works but any strong leak just pushes it out of the  way.  Dish soap in a qt. Spray bottle works best for me.  Even then you have to go slow and keep each fitting wet for several seconds.
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Lee Welbanks

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Re: Air pressure leak on coach
« Reply #6 on: February 13, 2016, 03:22:48 AM »
Good point Keith and with the soap the thicker the better, back in the day I've used almost pure soap and applied it with a paint brush but that was for a very very small leak.

Fred Brooks

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Re: Air pressure leak on coach
« Reply #7 on: February 13, 2016, 02:28:01 PM »
            Hi Al,
    Do you have an Air gauge with the green needle and a red needle? Are both going to zero or just the green needle. The red needle is for the rear brakes only and a dedicated tank. The green needle is for the front brakes and all air accessories. That is why you see it cycle between 90 and 120lbs because you re using air for the syspension in transit. Please advise, Fred
   
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Al Lewis

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Re: Air pressure leak on coach
« Reply #8 on: February 13, 2016, 09:21:43 PM »
More data. Yes the red and green needles go up and down together. I opened the engine service door and I have a quick disconnect port for an air hose attachment. I made up a fitting to adapt this to a Schrader valve and found the pressure to be zero matching the dash gauge. There are also four dump valves that I have never used. Opening the upper left found no air. Meanwhile the park brake and service brakes had pressure. Opening the other valves released pressure and the brakes stopped working. The ride height did not change. Starting the engine brought pressure up to 120-130 psi. Back under the coach and I find another air tank at the right rear. The other tank was in front of the rear axle mounted crosswise. With the Windex at the rear tank I found a significant leak at the fitting on a blue plastic line. This is probably the problem I am chasing. Anyone experienced at at redoing these fittings and if the parts are at home depot?  I wish I understood this system better. If you know where to find a schematic on an 02 Monterey with a ROadmaster/magnum chassis air system let me know.

Lee Welbanks

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Re: Air pressure leak on coach
« Reply #9 on: February 13, 2016, 09:56:50 PM »
Al,
Is the fitting a push-to-connect fitting? If so you can push in the rear ring and pull the plastic line out and cut off about a inch and then reinstall. Word of caution all these brake system fittings have to be DOT approved fittings and you will not find them at Homedepot or Lowes. About the only place that will have them is a truck shop or dealer.
Go on line and google Parker DOT air brake fittings, heres a pic of a parker push to connect fitting.
« Last Edit: February 13, 2016, 10:06:31 PM by Lee Welbanks »

Al Lewis

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Re: Air pressure leak on coach
« Reply #10 on: February 14, 2016, 11:41:11 PM »
Lee

Tho photo is not real clear and my connector giving the problem is a Tee but from your description I think it is the same. There is a ring closest to the line that pushes forward less than 1/16 inch and it releases the tube. I can see a fertile inside and assume there is an O ring. I trimmed 1/2 inch and reinstalled. I now get a minor leak but it has set over an hour and the gauge stays up within a couple pounds of the initial 120.  When I go to my truck store to buy all my filters and fluid I will see if I can get a new connector and replace. The air hoses are a real jungle and I hope they don't continue to fail. Again a schematic would be a help.

What are the four quarter turn dump valves?  I am thinking they may be to drain collected water. I have not opened them in ten years and no water came out. To my knowledge I do not have a dump valve for the suspension air bags. Thanks for everyone's help!

Lee Welbanks

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Re: Air pressure leak on coach
« Reply #11 on: February 15, 2016, 01:28:21 AM »
Al,
Glad to see you got the major air leak solved for now, and yes I would get a fitting to replace this one. You say it is a Tee, probably a swivel Tee which most of them leak.  I would advise you get non push to connect Dot air brake fittings which have a threaded nut, sleeve and the tube insert (old school). The mfg'ers went to these push fittings because they are so fast to install and it doesn't take any skill to push the tube into it and almost every one of them will start leaking sooner or later. I've replaced a bunch of them on my PT and have some more as I have a air leak in the leveling system.
If you post a pic of the Tee I could get you a Mfg part number for it.
« Last Edit: February 15, 2016, 01:31:57 AM by Lee Welbanks »

Al Lewis

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Re: Air pressure leak on coach
« Reply #12 on: February 15, 2016, 09:12:42 PM »
Lee

I guess I am lucky to find my first air leak on an 02 model using quick fit connectors. I will try to get an improved connector. Mine does not swivel but screws into the bottom of the tank with pipe threads. Then two blue air lines come out of it. I have not done photos on this site. I may not have the equipment or cables to accomplish. I am now using a kindle without photo capability. Maybe the iPhone 4 will work. Give me a short tutorial on what buttons to push.
FYI it looks like 24 hours will leak to about 70 PSI. Vibration will make it better or worse.

Lee Welbanks

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Re: Air pressure leak on coach
« Reply #13 on: February 15, 2016, 10:34:05 PM »
Al,

I don't do iPhone but there has to be something on it that looks like a pic of a camera. The Tee fitting is probably a male branch Tee, 3/8" tube x 3/8" tube x 1/4" MNPT. Here is the Parker # for a non push replacement VS272NTA-6-4. There are many mfg's of these DOT brake fittings, it would just depend on what your truck shop uses. If it has DOT stamped on it, it is a good fitting.

Al Lewis

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Re: Air pressure leak on coach
« Reply #14 on: February 16, 2016, 04:48:01 PM »
Attempting to include photo