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Question: why does the air leveling vale leak when at the correct height?
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Author Topic: 1992 Prevost xl air leveling problem  (Read 2122 times)
gyoder
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« on: July 20, 2013, 03:14:58 PM »

I brought the coach to the height it is supposed to be and blocked it up, the front leveling vavle is pouring air out of it, if I raise the body 1.5 inches the vavle will not leak. The air springs are supposed to run 11.5 inches high, the auto leveling will put it on the correct heigh but the front leveling valve leaks bad at that height , all I do is raise the body 1.5 inches and it will not leak, bad valve?
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robertglines1
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« Reply #1 on: July 20, 2013, 03:45:19 PM »

Sounds like you have level low system. Which I assume you have by your description . The leveling valve when you engage level low is taken out of the system.(by passed). When level low is disengaged and you hear leak it well could be the leveling valve. Make ??  Bob
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
gyoder
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« Reply #2 on: July 20, 2013, 05:33:43 PM »

yes it is a level low system, when I select drive the leveling valve should be functioning correct?
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Skykingrob
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« Reply #3 on: July 20, 2013, 07:38:12 PM »

I do not have a level low system on my 91 XL 40 but I had the same problem with the front valve leaking air. You have two options, buy an "o" ring kit and rebuild your present valve or buy a new valve. I bought a new one as I don't have the time to spend rebuilding. The kit was $27 and the new valve was $73 directly from Prevost including two day shipping. Get your VIN number and call Prevost, can't beat there service.
Point of safety, when under the bus to replace this valve, you will need to block the coach up and crawl in from the front to get to the valve. There will be no air support of the bus while this valve is being r & r'ed, so make sure your blocking is able to support about 20K pounds. There is a "doghouse" of sorts right behind the valve that you can sit up while replacing the valve.
HTH

Rob
91 Prevost
Missouri 
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luvrbus
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« Reply #4 on: July 20, 2013, 07:59:03 PM »

I had a problem similar to that on a H-41 I replaced the leveling valves and it still would do that, Prevost sold me the fluid,cover,delay piston plug,gaskets and o-rings to rebuild 2 of the height control valves then the problem went away 

Prevost really over engineered that system it is a PITA to chase some of the problems
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Jon
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« Reply #5 on: July 21, 2013, 04:35:33 AM »

I brought the coach to the height it is supposed to be and blocked it up, the front leveling vavle is pouring air out of it, if I raise the body 1.5 inches the vavle will not leak. The air springs are supposed to run 11.5 inches high, the auto leveling will put it on the correct heigh but the front leveling valve leaks bad at that height , all I do is raise the body 1.5 inches and it will not leak, bad valve?


The Prevost level low system is set up so when you manually raise or lower the coach the ride height valve (I assume that is what you called the leveling valve) is bypassed so that would make the air stop leaking from it.

The level low system seems overly complex until you get a basic understanding of how it functions and then trouble shooting problems is fairly easy.

To verify if the front ride height valve is the problem use the manual selector to the front position and make the bus go up or down and stop it at any point. You should hear no leaking at any height from the lowest all the way to the highest. Then move the selector to the driving or road position and see if the leak reoccurs. If it is back again just replace the valve. Your vintage coach uses a Haldex time delay ride height valve so expect a few seconds of elapsed time before you hear a leak or before it responds when the chassis is too low or too high.

Please, never ever get under your coach unless it is blocked or supported at the chassis support points, ESPECIALLY when you are working on the suspension.

There are articles on the suspension here http://prevostcommunity.com/articles.asp as well as some very good advice from Prevost owners on ther forum.
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Jon

Current coach 2006 Prevost, Liberty conversion
Knoxville, TN
gyoder
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« Reply #6 on: July 21, 2013, 08:54:37 AM »

Thanks for all the info,, Jon I went to the prevost community forum and there was a post there that explained the whole system, got my problem diagnosed, I am on my way
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robertglines1
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« Reply #7 on: July 21, 2013, 09:04:49 AM »

Takes a little to understand it! But when the lite goes on it makes sense. Level low that is.  Best of luck chasing leaks.   Bob
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Bob@Judy  98 XLE prevost with 3 slides --Home done---last one! SW INdiana
luvrbus
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« Reply #8 on: July 21, 2013, 09:57:00 AM »

The Prevost system is over engineered IMO MCI,Vanhool,Setra and others have the same feature with 1/2 the parts and valves
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Jon
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« Reply #9 on: July 21, 2013, 12:40:00 PM »

To add to Clifford's remarks about complexity all Prevost owners are faced with air leaks because of the number of valves and fittings associated with the suspension(s). Only an owner with a great deal of time and patience can find and fix all the leaks with the newer coaches now coming of an age when the push in fittings which replaced compression fittings are beginning to fail.

This relates directly to older coaches from the early 90's because the leveling system "logic" was such that auxiliary air pressure had to be maintained above about 35 PSI or the level low system would allow the tag axle control valve to shift and dump air in the tag axle air bags causing the coach to lean or drop suddenly.
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Jon

Current coach 2006 Prevost, Liberty conversion
Knoxville, TN
gyoder
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« Reply #10 on: July 21, 2013, 12:53:14 PM »

I own an eagle that I completely stripped and rewired it myself, I started back with just a framework,

  Saying that Prevost is over engineered is saying the least, I am just working on several local prevosts to help the owners out and they are both a nightmare. The one I am working on now has had 24volt hooked to the 12volt side, Its a 1992 with 44,000 miles on it and it has not been started for 6 years. i now have it running and transmission  gearing up and now I started on the rest of the problems.   
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Jon
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« Reply #11 on: July 22, 2013, 04:16:31 AM »

With 23 years of ownership and three Prevost coaches (87, 97, 06) I have learned to mentally separate the house from the chassis. That helps to simplify in my brain how and why things are screwed together the way they are. Maybe it is the years of working on my coaches that helps, but I know once a person gets to understand how Prevost assembles the chassis and its systems it all makes sense.

For example, we do not have a suspension. We actually have three suspensions (front, left rear and right rear) that happen to share an air supply. It may be simplified, but to Prevost's credit as the coaches have evolved the fundamental principle of the design has remained so a mechanic could do a reasonable job of diagnosing or repairing it. The electrical system is the same in that there are changes over time, but the basics remain unchanged. 85 is the ignition circuit for example, and it remains so for all model years.

The biggest problems I see is owners or mechanics do not take the time to understand the coach systems and they choose to rig up their own home brewed "repair". Over time that repair is forgotten and when someone else has to work on the coach they are faced with a hybrid that has modifications of questionable value. Now, with multiplex electrical systems it is more important than ever for mechanics to read the diagrams and learn the systems, which initially are seemingly complex, but in reality are a huge improvement. There never was a good excuse to jury rig repairs, and as the newer coaches filter down to the homebuilder that will be critical to understand.
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Jon

Current coach 2006 Prevost, Liberty conversion
Knoxville, TN
luvrbus
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« Reply #12 on: July 22, 2013, 06:20:38 AM »

One great thing about Prevost when it comes to the chassis is their tech support it's second to none IMO why people do not utilize it is beyond me  

Then I wonder where these buses will be on the resale end with all the high tech electronics the converters are installing no body will be able to repair one when the electronics are out dated and they go bad 

 I am running it to that on a older 2004 Creston system they tell me I need a new system mine is out dated $$$$$
« Last Edit: July 22, 2013, 06:31:23 AM by luvrbus » Logged

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Jon
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« Reply #13 on: July 22, 2013, 06:50:26 AM »

Clifford hit a nerve with me.

On the Prevost chassis I haven't found anything that Prevost did not support with parts or tech advice. Some items have been superceded, but Prevost makes kits to retrofit so they do keep the buses running.

The conversion if you buy a store bought conversion is another story. Early models without Crestron or devices built in (such as coffee makers) are pretty easy to repair and maintain. But when you get into the early versions of touch screen technology getting support can be an issue. Of course every converter will be more than happy to upgrade your coach to the newest technology but for a price that will take your breath away.

Don't get me wrong. I like sitting in my chair and touching a screen to open and close pocket doors or turn on the TV or make the shades go up and down or the awnings to come out, but I also know as the coach ages and stuff breaks I could be in trouble. I have zero concerns about the chassis.
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Jon

Current coach 2006 Prevost, Liberty conversion
Knoxville, TN
scanzel
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« Reply #14 on: July 23, 2013, 04:55:58 AM »

If you use the KISS method when building your own conversion you should be able to fix it yourself.
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Steve Canzellarini
Berlin, CT
1989 Prevost XL
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