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TEMP SENSITIVE SUSPESION AIR LEAK
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Glen, yea it makes one wonder how many others have rolled out of there and realized after getting the bill they still had the same problem ? Kinda like those folks who voted for obama !!
I`m planning air bag replacements this year at there mercy unless someone knows a highly reputable place in NC,SC or FL? Charlotte has plenty of big rig places that do that everyday, but know of no one who have used them for prevosts.
Keep us posted of your findings.
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I have been critical of technicians who return a coach with problems in the area of the repair work. But allow me to speak out of the other side of my mouth on this issue also.
The hardest repair on our coaches involves fixing air leaks. I have created two leak free coaches in my 23 years of ownership. My difinition of leak free is not as stringent as Hector’s in that if my compressor only comes on once in 24 hours it meets my standard. Hector’s definition is leak free as in not a bubble of air escapes. We will both agree to chase leaks is very time consuming and if you as an owner are paying someone plan on having a very large pile of Benjamins to start.
So when you bring in a coach with the “leans” and the solution is to not waste time and money chasing leaks, but to replace suspension related components such as air bags, fittings, Norgren Valves and maybe ride height valves I don’t think it is unreasonable for there to be a small leak or two that has to be chased after the job is done.
What does not strike me as reasonable however is to make owners pay for work outside the scope of the proper replacement of parts. Specifically everyone should understand if a coach has the leans it will be because there is a leak at the specific suspension where the coach is dropping. Isolating that leak will not require any investigation beyond the 5 port Norgren valve that locks in the air in that portion of the coach suspension and the air lines to the air bags, the fittings and in the case of the rear suspensions the 3 port Norgren valve between the drive and tag axles.
If the coach is leaning one side and then the other, both sides have problems relating to a leak. They both have to be checked.
But nothing outside of what I described will make the coach lean. And that includes the ride height valves. They are outside the 5 port Norgren valves and with the key off you can play with those valves, moving the arm up and down and no matter what you do the air that is in the suspension will remain in the suspension.
But if I wanted to get more money to chase leaks that I might have overlooked when I did the air bag replacement I might want to blame another suspension component so I could collect more money to justify the time spent. Am I being harsh? Yes. I am not saying a ride height valve cannot leak, because they do on occasion. I am saying they have nothing to do with the leans.
Keep in mind that if a new air bag or Norgren valve leaks it is very difficult to find those leaks. But good technicians have ways to isolate leaks and quickly find leaks an inexperienced owner may struggle to find. I cut them some slack, but only if they are honest with me.
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When I first took coach to Ft Worth it was a rise issue. Had to override leveling system to get it up there. After replacing rear ride height vales said it was fixed and ready for pick up. I was out my shop in Odessa Tx. and about 450 miles from them. Going up next day. Rodney called next morning and said had leaning issue on left side. Always took about a week to go down slowly. That was after rise height problem and been downhill ever since. Friday they replaced front leveling valve they said was leaking badly. Picked it up yesterday and it was down this morning. I will have replaced all valves in system i think. I have to count Hector’s diagram and see. Gremlins in system and spooks in the attic. I was rich before this started have sold half the herd and 2 dogs to science. The wife is next. Will keep yopu posted on ticket outcome. It might be interesting.
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Glens,
Your now famous!
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Glens,
Do not despair, the pneumatic leaks is very repairable, but my experience with Prevost Fort Worth was “not good” in this area. Hence, with blind determination and a bit of “hard headedness“, I decided to fix it myself. Prevost can very easily invade your wallet while chasing leaks. These Prevost pneumatic systems are manageable, but you will need to invest time in understanding how the system works. You can either do it yourself or direct others. Only then, can you hope to have a “air tight” bus. Depending on local shop individuals to have the detailed knowledge needed is doubtful.
I created the famous Texas Bubbler, recently copied as the Tennessee bubbler(You know who you are? Ha, Ha). With this device and a squirt bottle of soapy water mixture and of course coveralls, you can find all leaks.
Of course, the other option is to keep changing out components, hoping to find the leak or leaks. Remember, my comment is 95% of the leaks I have found have been in fittings. The the Prevost system has enough fittings to keep you entertained. I have found the Prevost supplied suspension components to be very robust. I have changed suspension components because of preventative measures, but never seen one leak. Others have had Prevost components leak however.
My 1995 Prevost has an aux air compressor that now cycles maybe once a day, depending on the outside temperature. That is acceptable for me. If the aux air compressor would start to cycle more often, I would do a leak check. I declared my bus “leak free” a year ago. After driving on a summer travel trip, the aux air now cycles once a day or so. But it is still manageable.
I live in Texas, so our ambient temperature are moderate considered to some areas. So the colder the outside temperature, the more you can expect leaks.
Good Luck,
Hector
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Glens, were you billed for the work and parts that did not fix your problem?
If so, how did they justify making all those unnecessary repairs and new parts?
JIM
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Glen,
As you have described your menu of problems you have bounced from the leans to ride height valves, and that is confusing because they are unrelated and only happen to be part of the total suspension system.
If you intend to chase leaks you have to define a specific problem and then focus on that, isolating everything else outside the scope of that issue.
When ever anyone speaks about a coach not rising to the ride height which is controlled by one solenoid valve in the stack, all 5 port Norgren valves and three ride height valves I determine if the problem is localized or associated with the entire coach. With that information the problem is simple to resolve. That problem has nothing to do with leaks. I am not suggesting the system is leak free, but if a coach will not rise to the driving height the problem is in a solenoid valve, a 5 port Norgren or the ride height valve.
The same can be said of the leans. Tell me where it leans and all efforts can be made in one area. The leans is always about air leaks. Hector is absolutely correct in that with some soapy water or a “Texas Bubbler” no leak will escape detection.
I made my first coach “leak free” working on a barn floor with it supported by hardwood blocks so I know for sure anyone determined can resolve problems by themself. Or a person can take the coach to a service facility, but never to one in which the techs do not understand the system.
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Thanks Hector for the invaluable advice!
Jim picked the coach up Saturday when shop was closed. Tech came in to open up for me. Haven’t got latest bill. I’ll know more in a day or two. First trip to them 4 weeks ago they they put valves on as follows—
Part # 641274 3way 2 position
Part #641528 3 ways 2 position N.O.
Part# 641531 5 way 3 position
also said on first ticket replaced several fittings that were leaking also. At that time they said airbags looked good. I was under coach also and they looked new. Tech asked me if I sprayed Armor All are something on them.No. Remember this coach I bought almost 3 years ago (how time flys) had been in a climate controled barn (with no windows I might add) and only had 50,000 miles on it when i drove it out of barn. Gen set 25 hrs. The leaning was a lot worse when they fixed the rise issue that just started a couple weeks before I took it up there. This time I had them replace bags and front leveling valve they said was leaking.
Will keep you boys posted with outcome.
The worst part about this is my wife says I can’t have an airplane cause of this cash cow. If you want to help send donations to Help Glen Keep His Sanity Fund at BLr 559- – – -.
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Glen,
I have some good news and bad news.
The good news is I can predict your bus will lean (or drop) in a predictable fashion and the solution is well known.
The bad news is that your level low system logic is such that as soon as the auxiliary air system pressure drops to around 30 or 35 PSI the three port Norgren valves located up on the frame between the drive and tag axles will dump tag axle air. That means part of your solution to the leans involves making your entire aux system leak free.
Both Hector and I should have noted that sooner, but I think we got sidetracked. Around the mid 90’s the level low system logic changed so a drop in aux system pressure would have no impact on your suspension or the leans. But unless your coach received the upgrade which I understand was about $1800, you need to maintain aux system pressure to keep the rear from dropping. Now that my feeble brain has kicked in it explains why you might have noticed the leans was going from side to side.
The tech should have known that. And I should have mentioned it earlier. My bad.
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I’ve had my share of “Wallet Vacuuming” done by Prevost as well as other “Knowledgeable” mechanics, but it begs me to hear Prevost Tech’s who do not fix our problems, or at least tell us the reality that our suspension systems present. I take into consideration changes made by converters, but really, if Apple tells me a Tech is working on my computer, they fix it ….period or tell you what is wrong. Doesn’t Tech imply someone who knows the product supposedly inside & out, after all it is their product. Sorry, no coffee today and being a Gemini, I will be ok later on.
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Our suspensions are evolving. As Hector created the power point program he had to focus on a specifc version.
What is important to understand is although the version in the power point program may vary from your specific coach or converter the underlying principles are the same.
Over the years Prevost has done an excellent job of steady improvements on our coaches. So have the converters. With each year come improvements and changes. If a Prevost tech, or any tech stumbles when providing service it is likely they have the same trouble keeping up with all the changes as we have. The suspension is definitely one portion of the coach that has had significant changes and while a Prevost tech might be up to speed on how Prevost has made incremental changes, it would be difficult to keep track of every converter and all the ways each converter has also evolved relative to the suspension.
I get that. It is easy to be thinking in terms of one iteration while trying to diagnose a different version’s issues.
But we as owners do have the right to expect $100 worth of expertise for each hour spent and I honestly believe as much as I (we) can be critical of Prevost I don’t have very many alternatives I would feel comfortable recommending to an owner that chooses to have work performed by others.
So to all owners, if you are having problems and issues with a specific area of the coach you are going to be better served and happier if you first clearly define the problem. Or each individual problem. Make notes. Be somewhat quantitative such as defining how long it takes to go from 120 PSI to 0 PSI, or how long it takes to lean 3″.
Ask questions of anyone you think has information that might relate to the problem. A lot of very accomplished people read these forums and the answers offered are of good quality. Remember diagnosing a problem via a forum is difficult at best, but the answers are still of value.
Make certain the tech actually understands what you have as a problem, and make sure he has satisfied you regarding how he will deal with it. Remember you may not know all there is to know, but the articles on this site can prove helpful in making you aware of what might be involved in dealing with your issue.
But more than anything else, if you choose to leave a coach you have lost control. Many of the folks who own their coaches but do not want to actually spin the wrenches have had great success by observing and making detailed notes on what was done and how long it took With that kind of attention it is likely the work is going to be done to a high quality level, there will be no question as to the time required, and there will be no doubt as to the scope of what was done.
And it has been said often, do not take Prevost repairs to a converter, nor converter repairs to other than the converter. There is no better expertise than that which resides with the folks that built it.
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If the Reverse Tag Logic hasn’t been done and the tag dumps on low aux air as it should, why would there be a lean from one side or the other? Both bags dump at the same time, or at least they should.
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They should, but do not always. The air pressure is required to work against the spring in the 3 port Norgren valve which is trying to return the spool inside the valve to the normal position, which in that case is normally open meaning it is venting tag axle air bag pressure to atmosphere, while blocking air flow from the drive axle air bags. Since spring pressures can vary slightly and the internal friction of the valve can vary it is not uncommon to have one side of the coach drop before the other. Eventually they both drop as aux air pressure continues to drop.
When aux air pressure is applied in excess of the 30 to 35 PSI required, the valve goes to the position which maintains an open airway between the tag axle air bag and the drive axle air bags.
If an owner never intended to lift the tag axle the three port Norgrens in the rear could be eliminated and the tag and drive axle air bags could all be joined with a common air line. But because it is advantageous to lift the tag axle on occasion the purpose of the three port Norgrens is to block air flow from the drive axle air bags, dump tag axle air bag air and allow the tag axle lift chambers to lift up the tag axle.
All late model coaches have system logic that maintains the open air path between all the air bags regardless of aux system pressure, only dumping tag axle air while “locking in” drive axle air bag air when it is necessary to lift the tag.
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Having just completed replacing all the rear air bags and Norgrens and most of the air lines, my coach has stayed up so far 3 days with no loss of height. That is as long as I have left it alone. It is now in the garage after our weekend trip and I will see how it does for more days. Before the change it had gotten to the point of dropping the driver’s side in 2 hours!!!
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Am I correct in assuming rear coach height should remain the same or at least close when tag is raised? I noticed this past weekend when tag was raised the entire rear dropped.
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