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Old 02-14-2006, 04:26 PM   #1
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Last weekend, I noticed both brake system air gauges start to cycle about every 4 minutes as we drove. By cycle, I mean that the compressor would come on, put the needles above 120lbs where they have always stayed while driving and within 4 minutes, they had dropped down below 100lbs and the compressor was on again. Fortunately, we were only about 20 minutes from the campground when this occured and we arrived without problems. We found a local repair shop who fixed the problem on Saturday.

The problem was a hole in a 1/4" line that runs in a bundle along the frame rail. The tech said that it looked like a puncture of some sort.

Sunday, on the return trip, I noticed that I am still getting some cycling but it is now more like 1/2 hour to 45 minutes between those cycles. Obviously, I still have some sort of a small leak.

Because of my experience in natural gas plumbing, I have no problems finding leaks around joints with soapy water. If my remaining problem is in the air lines themselves, however, I'm less confident about my troubleshooting abilities, particularly if there are bundles of lines together. I recognize that I could take the bundle apart front to rear and try using a strong light inch by inch to see physical problems. I'm worried that the leak is small enough that I'm going to miss it, even with the air tanks topped off at 120lbs periodically during my troubleshooting.

Does anyone have any other suggestions?
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Old 02-14-2006, 04:26 PM   #2
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Last weekend, I noticed both brake system air gauges start to cycle about every 4 minutes as we drove. By cycle, I mean that the compressor would come on, put the needles above 120lbs where they have always stayed while driving and within 4 minutes, they had dropped down below 100lbs and the compressor was on again. Fortunately, we were only about 20 minutes from the campground when this occured and we arrived without problems. We found a local repair shop who fixed the problem on Saturday.

The problem was a hole in a 1/4" line that runs in a bundle along the frame rail. The tech said that it looked like a puncture of some sort.

Sunday, on the return trip, I noticed that I am still getting some cycling but it is now more like 1/2 hour to 45 minutes between those cycles. Obviously, I still have some sort of a small leak.

Because of my experience in natural gas plumbing, I have no problems finding leaks around joints with soapy water. If my remaining problem is in the air lines themselves, however, I'm less confident about my troubleshooting abilities, particularly if there are bundles of lines together. I recognize that I could take the bundle apart front to rear and try using a strong light inch by inch to see physical problems. I'm worried that the leak is small enough that I'm going to miss it, even with the air tanks topped off at 120lbs periodically during my troubleshooting.

Does anyone have any other suggestions?
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Old 02-14-2006, 04:33 PM   #3
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Here's an additional piece of information. Since both brake systems where affected (and still are) by the cycling, the problem is apparently in the feed and sensing (I'm assuming that was the purpose of the 1/4" line) to the main tanks rather than in one of the brake systems. It appears that there are some sort of check valves which isolate the air going to the front and rear brake systems and those valves are mounted directly behind the tanks.

I've already been all over the joints around the tanks, including the bleed valves and there isn't a hint of a leak anywhere.

If I'm mis-understanding the system components, please feel free to correct me.
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Old 02-14-2006, 07:01 PM   #4
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How could the "Tech" tell there was a leak yet was unable to determine the line? Leaks do not self seal, therefore I believe you may not have a line leak. The symptons sound more like a leveling valve. Not necessarily malfunctioning. You stated 4 minutes or so then much more later for recycele. This may be normal deopending on the driving conditions, wind, load, etc. Short recharge cycles are common in some circumstances. You should do a shutdown at full air pressure and time the leak down while doing a walk around. Does your unit meet the required recovery time and hold down test?
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Old 02-14-2006, 07:24 PM   #5
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re-reading my comments I realize I did not explain the need for the leveling valves to loose air in the normal function of driving. The air leveling system relys on taking on air to lift a low point and releasing air on a high point to maintain a fairly level coach while driving. This requires the loss of air pressure due to the constant correcting of the air bag pressure while driving. Some road suface conditions, sway, curves and weather conditions can increase this function. requiring far more air production and loss than other conditions. Your description sounds like nothing more than what can occurr in normal driving. In some areas an air certification is not required. Those that must have this training and certification have the knowledge and ability to measure and test the air system on a dayly basis. If you are unaware of these test procedures you would be wise to take such a course to understand what is safe and what is not. I hope this helps.
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Old 02-14-2006, 07:39 PM   #6
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Thanks, Lugnut. I left out a critical piece of information - this is an XCS chassis and has no air suspension components. The air is only for the brakes (plus there is a small manifold for optional air horns, etc. but we don't have any of that). The suspension is all springs, similar to the Workhorse chassis.

The tech did find a failing line and fixed it with a splice. Afterwards, the cycle rate on the compressor was much different. My point is that prior to this trip, there has been NO CYCLING at all while we were driving.

I agree that a leak down test is in order but I strongly believe that it will fail in the current condition. I have the written leak down test procedure and plan to do it. I was just jumping ahead to what to do after that.
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Old 02-14-2006, 11:35 PM   #7
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I would start by rechecking the splice that the tech put into the air line. I bet there is still a slight leak at the splice. As long as the cycle of regharge is 30 to 45 minutes, I would not consider it unsafe; not perfect and what you would want it to be but you could drive it to get it home or to a shop if need be.
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Old 02-15-2006, 05:01 AM   #8
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Thanks, Mike. I agree with your assessment but am fortunate to have the MH parked at home and do not plan to drive it anywhere until I have exhausted all of the troubleshooting that I can personally do. That's why I was seeking other ideas.

I'll surely double check the splice. I'll probably also try to carefully examine that particular air line both upstream and downstream from the spice. Since the coach is 6 years old, I have trouble believing that this was some sort of manufacturing problem since it just now showed up. If the tech was correct and it was some sort of puncture wound, something created the damage and there might be more.

My concern was that the remaining leak is going to be a lot smaller and harder to detect. All ideas are welcome.

Charlie
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Old 02-16-2006, 12:34 AM   #9
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Charlie,

I was thinking a spray bottle of soapy water, magnifying glass, a bright light and a mechanics stethescope.

If it was a puncture then I would be looking for evidence of where whatever it was that caused it came from and where it went seaching for anything else along the path that may have been damaged also.

Hoping for your succes in tracking it all down.

Regards,

Neil
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Old 02-16-2006, 05:40 AM   #10
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Thanks, Neil. I was planning on using your first 3 items and appreciate your adding the stethescope to my thought process. I have one and maybe with that, I can hear air escaping along the hose runs that I might have missed with my "naked ear".

I didn't get a chance to see the original "wound" and agree with Mike that checking that area for another leak is a good idea. I can easily find the splice and will look around it. I do know, however, that the damaged hosed was in a bundle and the tech had to separate it out enough to put the splice on. I cannot imagine what could have punctured the line in that configuration.

I'm also going to be examining the lines for flexibility. It may be that one or more simply is too brittle and cracked.

I have a couple more days before I will have time to spend on this problem. Please continue to provide any new ideas that you have.
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Old 02-19-2006, 09:48 PM   #11
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I'm going to bounce this back to the top one more time with a question. Before the tech found the hole in the line, he mentioned something about the parking brake valve possibly leaking. Has anyone heard of this? Is there any way to check for an internal leak on that valve? As I said in the original post, I'm a tiger with a soapy spray bottle but I'm stumped about how to diagnose leaks in the air system without taking things apart. The valve would be one of those, I guess.

Thoughts?

Charlie

P.S. It was too blinking cold here this weekend to even think about troubleshooting this problem. We are supposed to get a big warm up again before next weekend.
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Old 03-01-2006, 06:11 AM   #12
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Yesterday morning, I finally had time when the weather was good to try to troubleshoot this problem. With all my tools in had, I started at the compressor, checking every joint carefully and making a drawing as I went. Before crawling under the chassis, I checked the manifold in the front compartment (where the air horn tap would go) and found a leak in one of it's plugs. After dumping the air and then removing and resealing the plug, I started the engine and recharged the air system, allowing it to stand overnight. This morning, I'm down to just a shade under 100lbs. That's a signficant improvement because the air alarm has been coming on at less than 65lbs when I parked overnight.

I tried using a regular doctor's type stethescope to find the leak without success. Either I'm not listening for the right noise or was able to position the end of the stethescope to hear it. I found the problem with my soapy water spray bottle.

Obviously, I still have a 20+ pound leak in 24 hours and will work to find the additional sources of it. BTW, I carefully checked the splice that was installed and can find no sign of a leak there. I suspect the remaining leak is going to be difficult to find because it is even smaller than the original one.

I'm still solicting information about the parking valve and any additional troubleshooting techniques that would make this process easier.

Thanks,

Charlie
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