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Tag Won’t raise, 1 Tag Bag Won’t Inflate
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I guess I didn’t make myself clear in my last post. All 8 of my airbags are working properly in the travel and manual leveling modes. Evidently, by having pipe plugs in the exhaust ports of the two 3 port rear airbag relay valves(K910026) that someone recently installed on our coach has the same effect as Jon described. I hope to find out from Liberty Monday what rear airbag relay valves are suppose to be on our coach. Some coaches have normally open valves, and some normally closed. Our currently has two Norgren K910026 with are normally closed.
This is my 5th tag axle MH. I know how unimportant this feature is. It’s the last of my concerns. The passenger side tag raise accuator tries to raise the tag axle. The driver side doesn’t. It either has a hole in the camber or in the line going to the camber. Easy fix.
I’ll ask this question again: do the schematics depicted on the PrevostCar website depict all the changes made by the converter????????
I asked “is the aux air system tied into the accuation of the tag bags” in a previous post and didn’t get a reply. I see in the schematics that it is.
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I believe your last two questions were answered, but here they are specific to your coach. Liberty has modified the Prevost system, but the modifications have no affect on what has been discussed.
The aux air system is what provides the air for the suspension, so any and all suspension functions are at some point tied into the aux system. More specifically the tag axle lift also gets air from the aux system.
The 3 port Norgen valves can be installed so the air goes through the normally open path, which is what is happening in the case of your coach to keep the tag inflated along with the drive axle air bags. Prior vintage coaches had reverse logic that required aux air system pressure to hold the path open. On your vintage coach your aux air can go to zero PSI and the air bags will remain inflated as long as there are not any leaks.
Didn’t you say the tag air bags were not getting air and that as a result the axle weight (when I finally learned how to read) was only 6000 pounds? What has changed so it is getting air?
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are the way it left the factory to be converted by whom ever. Is that S followed by a 102? that would indicate a 1995 chassi.FWIW Mine is a 1998 and is a W .I also have owned a 1997 with a V as the last letter in the serial Number. If you call Prevost they will give you the history of the coach when it was deliverer to be converted etc. That is where they stop. The converters and others do as they will.. the basic bus is tough as nails. It was practice for a converter to title a coach as the year it was converted not manfactured by Prevost. Bob
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I’ll ask this question again: do the schematics depicted on the PrevostCar website depict all the changes made by the converter????????
No, it does not…
Liberty modified your system because of the auto level. You have (2) 3 ports in your steering bay that control the (2) 5 ports mounted on the firewall in front of the drive axle. They did not modify the tag lift or tag air bags.
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When I drove the coach home(TX) from the seller(FL) the passenger side tag bag was empty and the airbag relay valve(K910026) on that side didn’t have a pipe plug in the exhaust port. The driver side tag bag was inflated and both the airbag relay valve(K910026) and the tag accuator valve had pipe plugs in their exhaust ports. As a result the tag was carrying a partial load(6060 Lbs).
As it stands now, I have put a pipe plug in the passenger side airbag relay valve(K910026) and removed the pipe plug that was in the tag accuator valve(no part# on it).
The schematic that came in the mx manual(D140202 rev D) shows normally closed airbag relay valves, and a normally open tag acc valve. Schematics D140211 & D140212 show just the opposite type valve. None of the schematics show the manufacturers part#s. At this point in time, I don’t know if the two relay valves(K910026) or normally open or normally closed valves, and I don’t know if this is the correct or incorrect relay valve for or system. And since the tag accuator valve doesn’t have a part # on it, I don’t know if it is correct or not.
Hopefully Monday Liberty will have some answers?
Thank You
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Don,
We are not familiar with the term relay valves, but in the context of the discussion I have been assuming you are talking about the 3 port Norgren valves mounted on the frame up high between the tag and drive axles.
Try to understand while they are hooked between two air bags (one on the drive and the other one being the tag) that they just sit there and don’t have anything to do with the suspension except when you want to lift the tag axle. Then the normally open path through them closes and the air in the tag goes out the exhaust.
What you have made clear is that the coach has been messed with. So if you try to not focus on part numbers and diagrams and accept the fact that you don’t even need them until you want to lift the tag (an extraordinarily rare event BTW) you can at least know if the rest of your suspension is messed up or not. While talking to Liberty will be productive, there is nothing worse than being asked to diagnose a problem with only bits and pieces of information instead of seeing the whole picture all at once. At this point nobody even knows if the valves you mention are plumbed so the air is flowing through the valve or is blocked by the valve.
Try to sort out if the system works as it is supposed to. The tag axle lift is another unrelated topic, but with the suspension system working, then the tag lift issue can be resolved. One thing you should understand is that on your specific model coach it is likely you can lift the tag axle if you are willing to wait. On a perfectly maintained coach lifting the tag might not be capable beyond getting some weight from it. When the tag air bag air is exhausted the weight carried by the tag axle shifts to the remaining two air bags on the rear axle so the rear is going to drop. If you can build enough pressure to inflate the drive axle air bags to restore the coach to the ride height the lift chambers may not have the ability to lift the tag. But if they can lift the tag it will only be after the coach rises back to ride height, something not assured depending on how much total weight has to be supported by the drive axle air bags.
When you do try to lift the tag you are not only transferring the weight of the tag to the drive axle, you are also shifting some of the weight carried by the steer axle back to the drive. But lifting the tag is another entire issue.
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Don
I notice in the schematics you post at the begining of this thread that tag lift is labeled “Optional”. Do up know if your coach even left the Prevost plant with the option of lifting the tag? Maybe someone has converted it to do so and just didn’t do a very good job. The picture with all the pipe plumbers seal doesn’t look like Prevost or Liberty’s work, especially if they are floating loose with just the tubing holding them.
Greg
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I’m a retired pilot w/type ratings in six jet airplanes. I spent many years studying, understanding, and operating all kinds of systems. When aircraft systems were repaired the quality of workman ship was always high.
This is our seventh MH(depreciating asset). We always buy used big dollar depreciating assets. I’m a DIYer. The quality of workmanship I’ve seen in past repairs to our MHs has been poor. Nothing surprises me anymore.
Other than the mess someone has made with the rear airbag valves, the rest of the tag raising system looks original to me so far.
Thanks
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in that particular yr range lots of changes were going on . That is why yr and unit questions early on. One change was some coaches just releasing air from tag air bags with no lift air cans to lift them further…Also coaches were designed that when you turned ign key off it automatic dumped air from tag axle bags. Lots of things changing then. Some mechanics do not realize this was happening some times in mid yr. Best of success with your coach..
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If it were my coach I would by-pass the messed up valves merely to confirm the rest of the suspension was not altered. That makes your conversation with Liberty much more productive because you are able to discuss the entire issue.
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Don
I know you want to get your coach back to the original design. Jon I think is not say bypass the problem and leave it that way, which I think you are resisting. Jon is saying bypass the lift system and see if everything else works as designed and if OK you have narrowed your problem list down.
GregM
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Where to start?
I ‘ll start by saying I’ve got the leveling system working normally in the travel and manual leveling modes. The tag bags hold air even when the aux system leaks down.
Relay valve? I got the term off a pneu schematic. See D140212 item#s 32, 33, 79. So we’re on the same page I’ll try to remember to call them 3 port valves.
I called Liberty this AM. They said the only thing they added was two left and right 5 port valves in the steering compartment.
I called PrevostCar customer service again. They told me the K910026 valves that are presently installed and control the rear airbags on my coach are correct and that they are normally closed. Then they told me there was some old Service Bulletins. I checked the website and there was two: #96-13 & #96-14B. I don’t believe #96-13 is worth talking about, but #96-14B(Sept.1996) is. It’s purpose is a “product improvement” in nature, not “safety” related. Modification includes: changing the logic of unloading and retracting the tag axle. There is a long list of parts associated with it. New 3 port relays valves, new tag accuator valve, the addition of an inversion valve, lots of fittings, some electrical changes, etc.
The best I can tell this service bulletin, #96-14B, has NOT ever been performed to this coach. Go figure? One owner from 1996 to 2012 and they didn’t have this done? Wow?
Since it’s operating good, I’m ready to go back to work on fixing the dash curcuit of the OTR ac.
Thanks
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Where in Texas are you?
You have Prevost Ft Worth and Prevost Houston that can help you…. at least to tell you what is or isn’t altered.
At least to find out where you really stand.Cheers,
Diane -
You may be talking about the stabilizator eliminating modification. Not all owners wanted that capability eliminated.
JIM
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Don……
What remains unanswered is why originally your tag air bags were not inflated, and now everything is OK.
None of our coaches repair themselves.
What Prevost explained I believe is the change in system logic. Early vintage coaches required aux air pressure in excess of 30 to 35 pounds to hold the 3 port Norgrens between the tag and drive “open”. If aux pressure dropped below that value the valve would shift, and tag axle air bag pressure would be exhausted.
We do not know from your signature line if your coach has the newer system logic in which aux pressure could drop to zero PSI and the three port valve would remain as an open path between the two axles. All newer coaches have had that modification. Those earlier coaches with the “reverse” system logic would be OK until aux air pressure dropped and then the valve would shift, you would hear air excape and the rear would drop because the tag axle air bags were no longer supporting weeight.
I do not know what serial number was the beginning of the current logic. If yours precedes that there still remains questions about what was modified on your coach to create the problems you have previously described.
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