FRONT AIRBAGS

[Jon Wehrenberg]

Several years ago the King and I decided to change all the air bags on our coaches. The incentive was that Roger wanted to change them, but Prevost had shipped the wrong front air bags.

I ordered both sets for our coaches, but in doing so I found the Prevost parts folks in Elgin had a high potential to ship the wrong air bags. I spent quite a while with the parts guy until we both agreed on the proper air bags for Roger's coach and mine. Specifically we got 630126 air bags for the front axle of our coaches (now superceded by 630259) and not the air bags listed on the bill of material. The air bags listed appeared to be for a seated coach, the significance of which is important.

Our motorhome shells are designed to have about 4" of both up and down travel from ride height. The purpose is to allow leveling on uneven campsites. A seated coach is designed to go down (kneel), but not be raised above normal ride height. It is likely that anyone that orders air bags for their coach or has them replaced by Prevost is not going to get airbags the equivalent of what was on the coach when it was built. Prevost continues to ship and install the wrong airbags on motorhome coaches.

This is a critical piece of information that everyone should know and understand. If you are going to have air bags for your coach replaced there are some things you should do. First, measure the ride height, the lowered height and the maximum raised height of your coach. The proper way is to measure the distance between the upper and lower air bag mounting plates, but it is just as easy and understandable to measure from the bottom of the bay door just behind the front wheel to the floor surface. When having the air bags replaced be certain that the installer understands you need to retain the amount of travel you have, and that if you do not get that travel with new air bags they need to be replaced with those that will provide the travel.

There are other issues related to this that all of you should know. First, the current air bags being supplied have larger fittings for the air supply, and the top mounting plates on some coaches do not have a hole large enough to accomodate the fitting. The hole in the top mounting plate in that case may need to be bored or torched out to a larger diameter to accomodate the fitting in the top of the air bag. Another issue is travel. While it is important to retain the amount of vertical rise above ride height, it is equally important to not have an air bag that will provide more travel. It is possible to break the top mounting ring from a shock absorber if there is too much air bag travel. A broken shock absorber can do some damage so it is important to not install airbags that can break the shocks.

There are some coach owners who now have air bags on their coaches which do not allow any travel above normal ride height. If this is not a concern it should be. Because we take our motorhomes into some campgrounds that are not as flat or level as the streets a seated coach will encounter, we may have to raise the front above normal height so the front of the bus does not scrape the ground. If we have to be put on a flat bed trailer we may need the extra height to prevent damage to the front. If we have to clear a hump to prevent damage to a low hanging generator baffle we may have to raise the front. These reasons go beyond leveling the coach at a campsite.

I do not know specifically if this situation exists with H3 or XL coaches with IFS, but it could so be alert and take the same precautions if air bags have to be changed.

If you allow yourselves to become a victim of reduced height due to the wrong airbags remember Prevost will not correct the problem. To their way of thinking the air bags they list and install are what is called for in their parts lists and they will not do anything to correct this so it is up to you to get an understanding from Prevost up front as to what you expect after air bags are replaced. It may not seem like a big deal now, but if you damage the lower front of your coach or wipe out a generator baffle because you cannot raise your coach up this issue will take on a greater significance.

[phorner]

Our bus is a 1999 IFS shell.

When the front air bags were replaced, the replacements were part number 630151. We retained the correct travel and there were no issues with the top mounting plate hole diameters as ours had the larger air lines in place.

These were installed in June, 2008, so I'm assuming (dangerous thing to do) that these are still currently available. I have no clue as to whether they are acceptable for non-IFS shells, the top plate mounting hole diameter being another issue.

[Kenneth Brewer]

Jon,

If you haven't sent a copy of your post to Prevost, please do. As high up the chain as possible. If for some reason you are reluctant to do so, perhaps others of us should, although it probably won't carry the same weight individually. Thank yiou for this post; it is very important, in my opinion. Good job, once again.

[Jon Wehrenberg]

Ken,

This is a sore subject with Prevost. Joe C and I have addressed this problem. Joe was the last one to tackle the issue, and he did it with Bill Jensen and got blown out of the water. Bill will be in OKC so we can address this again with him. He is responsible for all Prevost Motorhome maintenance.

When I first learned of it was when Roger got the wrong airbags and I worked directly with a parts guy to work around what the bills of material said to get the correct air bags. Joe and I had many discussions about air bags and he got directly involved in it when he replaced airbags for someone and they could not raise the front. He was very persistent trying to get it corrected and got shot down in flames.

I posted the way I did for a reason. If Prevost has a bunch of motorhome owners want bags replaced, but conditional on having their motorhome leveling system work as intended, after Prevost ends up doing the job over and over until they get it right some changes may take place. Prevost has changed. At one time they were the standard by which I measured all other companies I dealt with. Now that the name Volvo is on the front door those days are gone.

Essentially they rely on owners not catching the issue until it is too late, or they rely on owners willing to roll over because they say this is the way it will be. I have worked my way up the food chain on this issue, not exclusively about them using and supplying the wrong air bags, but because they insist it takes $500 to replace an air bag. For your information an air bag costs about $140 and it takes about an hour to replace. I tackled the issue with Guy French who is near the top of the food chain and got nowhere. Joe's battle followed mine and he had the same results.

[phorner]

That's an excellent point, Jon.

If Prevost has to start shelling out cash to replace air bags that do not perform, after a while they very well might start taking the issue more seriously.

I very much like demanding a performance specification to determine whether a job is "complete" or "satisfactory" or not. The job isn't complete unless and until the new installation works to the same specification as the original.

Great post!

[tdelorme]

Jon, seems kinda dumb to ask, but have you or Joe checked with Goodyear or Firestone for a proper replacement of the original Prevost bag?? Surely Prevost wasn't the only company using the bag that they no longer have in stock.

[Jon Wehrenberg]

For the moment that is not a path we feel comfortable taking.

I have what are industry trade numbers for the correct air bags for my bus. They are proprietary and are not listed for sale anywhere I have been able to find. Apparently Prevost has them built to their specs. In the past I have been able to cross reference the numbers on my old coach so apparently at that time Prevost was using generic air bags.

My reluctance stems from something Dale J pointed out. He correctly stated that the limiting device for our front suspension travel is the shock absorber. That creates an issue. Any air bag used has to have the correct diameter so it does not interfere and rub on any of the wheels or front suspension parts, but has to be big enough so it will lift the front end with minimal pressure. This is a critical consideration because if the diameter is too small some coaches with heavier front ends may not come up to ride height. That was the whole reason for the switch many years ago to the "Mae West" airbags. But in addition it has to have the correct inflated height. Too little and we end up with insufficient height, too much and we have the potential to pull the end rings off the shock absorbers.

The final consideration is the air bag has to have the rubber bump stop internally to support the coach when the air bag is fully deflated.

Add to those serious considerations the need for the correct mounting holes and air inlet size and you can see that shopping in the parts bin for a generic air bag is difficult. I think Orren (who is the King of Heavy Duty Parts) is aware of this situation, and if we really get in trouble we may have to see if he can lend his considerable contacts and expertise to this problem.

[truk4u]

Jon,

If you want, I'll get this issue to Bill and his boss for a heads up before OKC.

[Jon Wehrenberg]

As a courtesy he should be alerted, and rather than blind him with a question, would he want to bring the topic up himself?

He really got into it with Joe so this may get a little touchy, but our coaches have a leveling system and it is being compromised if the bags now being supplied for certain models (and maybe all) will not go beyond road height.

I think it is a good idea to address this.

[dale farley]

Jon, This is an excellent post, and it affects many of us in numerous ways. I have a steep driveway. The highway in front of my house was paved twice last year, and that changed the angle of attack that goes from the highway to my driveway. I now have to raise my bus beyond normal travel height to get up my driveway. If I changed to air bags that do less than my original ones, I would drag the front and rear of my bus every time I go in or out of my driveway.

[Kenneth Brewer]

As a courtesy he should be alerted, and rather than blind him with a question, would he want to bring the topic up himself?

He really got into it with Joe so this may get a little touchy, but our coaches have a leveling system and it is being compromised if the bags now being supplied for certain models (and maybe all) will not go beyond road height.

I think it is a good idea to address this.

I know I am wacking a hornets' nest with a stick to see what happens, but; how/why did he 'get into it' with anybody if Prevost is/was wrong in providing the wront bags to customers? Who else is supposed to have the proper information? Why is the customer/owner being saddled with the task of finding out what the hell to order? Was the response that the owner should have gotten the number off the bag(s) to be replaced? That won't fly either.

Sorry.

[phorner]

Just a quick question; do we know if this problem is confined to a specific range of XL shells?

Have any of the IFS chassis had a similar problem in finding replacement air bags?

[Jon Wehrenberg]

Ken, If you think you are going to be criticized for thinking like that you are wrong. Your thoughts and comments are exactly right.

We discussed this briefly at Roger's house with the other POG folks that were there today. It started about six months ago when Joe changed the front air bags on Eric and Deb's coach. It would not rise to the previous level and through a considerable effort he or they were able to get Prevost to ship bags that would restore their ability to travel the full range in height.

It was later learned bags ordered and installed on other coaches had the same problem with limited height, and then since a pattern was now established Joe pursued this with Prevost, eventualy working up the ladder to Bill Jensen. According to Joe his representation that Prevost was shipping the incorrect air bags was met with the comment that the ones shipped and received were what the bill of material called for and therefore they were right.

Through some effort on Joe's part he found the 630126 bags (that work) were superceded by 630260 (which do not work because of limited vertical travel), but that 630259 do work as replacements.

They have other issues, such as now having to rework the mounting plate hole on some early coaches. As things exist now an uninformed owner who gets air bags changed or orders new ones is going to lose some of the capability his coach was designed to have.

I brought this up to keep it alive. Joe and I spent a considerable amount of time discussing this issue and pursuing it. Truk (who is the Prevost contact person for the OKC rally) is going to let Bill know we intend to discuss this, because we are sure some owners have air bags now installed on their bus that do not have the vertical travel their suspension system leveling feature was designed to have.

You can be assured we are not shy about raising issues like this and if you wish to join in we welcome your comments.

I would like to know what converters do to handle this because if they do a full PDI on a coach and determine it should have new air bags they may have the same grief.

[Jon Wehrenberg]

Paul,

We do not know, but we do know it is an XL solid axle issue. It may affect other shells, but until someone can tell us they had air bags replaced and now the height has been compromised we will no know.

At OKC why don't you see if all IFS coaches can demonstrate the max height they can go in the front and see if any had recent air bag replacements?

[garyde]

Any one else having problems with the quick reply button?
Anyway, Jon, is it possiblle to develop a spread sheet indicating the correct replacement air bag # for the XL's in question or are there too many different air bag types. Also, are al of these Goodyear Airbags?

[tdelorme]

Is it possible that Prevost has seen such a steep decline in the sale of Motorhome shells that the "new guys" up there aren't concerned a bit about parts being unavailable for older motorhome shells? We may well be at the end of the line of Prevost conversions in significant numbers. You think the powers that be, at Prevost, have had an eye on their motorhome shell sales. Do any of us really expect to ever see the number of convertors in business that were around ten years ago. I'm just saying, when Bill Jensen starts dancing around an easy question, he's hearing music playing somewhere. When it comes to parts that are specific to our motorhome shells, we all need to be active in the aftermarket arena and be willing to share that information like we do everything else.

[Kevin Erion]

Jon,
I think another fun Question to ask Bill would be how engineering would allow the shocks to be the limiting travel in the overinflate position. Pulling out rubber bushings and even possible damage to the shocks from the air bags trying to go up past the length of the shock!

[Jon Wehrenberg]

These are all good points and since Truk is talking to Bill about the rally and his role in it I am sure he will pass this along.

We can ask the hard questions without feeling bad because we will not be sandbagging Bill. He is being given a heads up and as such will have plenty of time to prepare or get answers.

BTW, I think the airbag issue is a serious and widespread one and should be given the attention it desreves, but that does not mean that other issues cannot be brought up. If there is an issue related to the chassis, or with Prevost that anyone feels is in need of an answer or attention I suggest it be listed here and Truk can pass it along to Bill.

In defense of Prevost I urge that we keep the questions to those of general interest, and that we post them here so Bill can be prepared.

[JIM CHALOUPKA]

Tom, I would like an explanation by Bill Jenson of the workings/the way it works, of the two speed fan and clutch assembly.
There are magnets, sensors, heat, sinks,and the mechanical shaft and bearings.
How do they inter relate and what controls them?

JIM

[JIM KELLER]

My Bus is at the point where I am considering new air bags. I am willing to spend the money but until this issue is resolved Prevost won't receive any of my hard earned cash. In a market where new Bus sales are down I think it is prudent to take care of service related parts and labor. Our Sponsors are trying hard for their share of our business and I think Prevost should also. Just my humble opinion.

[rahangman]

Several years ago the King and I decided to change all the air bags on our coaches. The incentive was that Roger wanted to change them, but Prevost had shipped the wrong front air bags.


Our motorhome shells are designed to have about 4" of both up and down travel from ride height. The purpose is to allow leveling on uneven campsites. A seated coach is designed to go down (kneel), but not be raised above normal ride height. It is likely that anyone that orders air bags for their coach or has them replaced by Prevost is not going to get airbags the equivalent of what was on the coach when it was built. Prevost continues to ship and install the wrong airbags on motorhome coaches.

This is a critical piece of information that everyone should know and understand. If you are going to have air bags for your coach replaced there are some things you should do. First, measure the ride height, the lowered height and the maximum raised height of your coach. The proper way is to measure the distance between the upper and lower air bag mounting plates, but it is just as easy and understandable to measure from the bottom of the bay door just behind the front wheel to the floor surface. When having the air bags replaced be certain that the installer understands you need to retain the amount of travel you have, and that if you do not get that travel with new air bags they need to be replaced with those that will provide the travel.

There are other issues related to this that all of you should know. First, the current air bags being supplied have larger fittings for the air supply, and the top mounting plates on some coaches do not have a hole large enough to accomodate the fitting. The hole in the top mounting plate in that case may need to be bored or torched out to a larger diameter to accomodate the fitting in the top of the air bag. Another issue is travel. While it is important to retain the amount of vertical rise above ride height, it is equally important to not have an air bag that will provide more travel. It is possible to break the top mounting ring from a shock absorber if there is too much air bag travel. A broken shock absorber can do some damage so it is important to not install airbags that can break the shocks.


If you allow yourselves to become a victim of reduced height due to the wrong airbags remember Prevost will not correct the problem. To their way of thinking the air bags they list and install are what is called for in their parts lists and they will not do anything to correct this so it is up to you to get an understanding from Prevost up front as to what you expect after air bags are replaced. It may not seem like a big deal now, but if you damage the lower front of your coach or wipe out a generator baffle because you cannot raise your coach up this issue will take on a greater significance.

OK, so if I have this right, (I fall into the late 80's early 90's category) If I go to Prevost they will put in 2 new airbags (after enlarging the mentioned access hole) that will not raise my bus over its required ride height. I will be in a pickle for some manuvering which could cause damage. If I put the other air bags in that could possibly raise my coach beyond the 4" excess height, I could pull apart a shock and also cause damage. SO if I then decide I should change my shocks to prevent an overheight inflation situation, can I find shocks that will be long enough when extended to avoid this? Conversely as mentioned by others, maybe a different airbag other than Goodyear 259 or 260 can be found? I must say this is a stimulating subject and I thank the MPD Gods for guiding me to POG to provide this assistance.
__________________

[Jon Wehrenberg]

I do not know of any shockes other than those supplied for our coach. There might be some out there, but my guess is if the shocks extend further so breaking the rings (or as Kevin points out ruining thE bushings) they will not collapse enough so the lowering travel may be compromised.

That is why I suggested if anyone is going to replace front air bags, just prior to having it done measure the lowest height and the highest height and the ride height, and let the service people know those are the range of dimensions you expect and require.

If they cannot assure you they can do that, I suggest you not get the job done.

[Orren Zook]

Increasing the port size on a bag will do nothing to increase air volume unless all associated air lines, fittings and valving size (inside diameter) is also increased. I would guess that the increased inlet size on Prevost air bags is to speed up the kneeling process and recovery to ride height for transit coaches and would have little benefit for any motor coach conversions with smaller diameter air lines. Sounds like the old adage: "sell 'em what you've got, not what they want".

[Jon Wehrenberg]

Orren,

Your analysis is correct, however Prevost may be attempting to reduce line items in inventory. The current coaches use an accumulator tank pneumatically tied into each air bag. However, while my coach has a larger diameter fitting and air line going into the air bag in the front, the controlling orfice is either in the ride height valve or Norgren 5 port valve which are in line, or the air hoses to or from them, which in all cases is smaller.

I do know from conversations with parts personnel that there are or has been a lot of different air bags listed for 40 footers, 45 footers, motorhome shells, seated coaches, etc. This entire issue may be a result of someone's attempt to reduce the number of variations they stock.

[tdelorme]

I know we're beating this horse to death, but just for the record, do we know who made the original front bags for motorhome shells?? And, do we know a part number other than the original Prevost part number? I've got a NAPA parts guy that can cross reference up a storm and I sure would like to give him a shot. In fact, if someone has the original Prevost part number, he can usually use that.

[bluevost]

Jon, Truk, and other POGgers

The following comments apply to my solid axle coach, chasis vintage 1994:

On March 3, 2008 I had Bluevost in the Prevost Mira Loma service center for service. Using the "Werenberg 10 year rule", I requested to have the front bags removed and replaced with new ones. The part number on the new bags is 630259. This is not the same part number as the originals. I still have the original bags, but they are in California and I am in Connecticut, so I can not include that part number here.

I have not been able to satisfactorally raise the front of my bus since. I can't tell you how many times we have camped with the front of the bus low. Level low will not do it, and the automatic level will not do it.

I planned on talking privately with Bill J at OKC. This was not of my doing. Shouldn't Prevost change the bags to the correct bag, at their expense?? Even though it has been 1 1/2 years.

Makin' our way (round about) to OKC,

Ken

[phorner]

Ken, I agree with you. There is more to an air bag than simply being able to hold air without leaking.

You have lost an important part of the performance of your front air spring suspension system, which rightfully ought to be restored at the expense of the service center that provided the less than satisfactory installation.

[grantracy]

Just replaced mine as well I guess I will dig out the work order to see what was installed. Had to have it back after the installation to repair air leaks and install missing hardware. Did not leave me feeling too confident about their abilities.

[Jon Wehrenberg]

I know we're beating this horse to death, but just for the record, do we know who made the original front bags for motorhome shells?? And, do we know a part number other than the original Prevost part number? I've got a NAPA parts guy that can cross reference up a storm and I sure would like to give him a shot. In fact, if someone has the original Prevost part number, he can usually use that.


The problem Ted is what number do you want to cross reference? My bus has two different part number air bags. Those air bags are not the same as for a 40 foot bus. A seated bus has different numbers. An older coach has different numbers and fitting sizes whether it is a motohome or a seated bus. We don't even know the extent of this issue yet. Does it apply to H3 owners? IFS owners? If the Prevost part numbers we have are converted to industry numbers (my now obsolete Prevost 630126, industry part number 1R11 296) is a proprietary air bag specifically for Prevost. I am not willing to risk using a Firestone apparent duplicate even if it can be cross referenced unless I can be assured it has all the characteristics including diameter, height, internal bump stop, etc.

We can use the internet to cross reference until the bovines arrive back at the ranch, but first we have to get at the truth as to what air bag is supposed to be on each coach.

As we hear from folks like Ken and maybe Granville (who has an IFS) we are going to learn more. I do know this, Folks like Dale F and myself absolutely require the capability to raise the front of our coaches as high as they are designed to go because if they do not raise sufficiently both of us are going to do some damage under the coach. Others are likely to be equally affected and may not know it yet because they don't routinely have to have full up travel in the front.

[truk4u]

Ken,

Mine is a 94 (93 chassis) and I have 259's on the front and 630104's on the rear. I have full travel both front and rear.

[Ray Davis]

I *thought* that Jon had mentioned the 259's were the numbers of the new correctly working bags?

[LA-HODAG]

I have had exactly the same experience as Bluevost. I had mine replaced at Mira Loma two years ago and have not been able to lift the front properly since. I discussed this issue with them several times, until they finally convinced me that I was crazy and the bus never lifted any higher than it does now. I guess it is probably too late to do anything about it now, but it is gratifying to know that they were gaslighting me and that I am not actually crazy. I won't back down to their B.S. in in the future. Thanks, guys.

My bags were replaced before Volvo took over, so I can't blame the new owners. But I must say that I have been not just disappointed, but actually disgusted by Prevost service at Mira Loma over the past year. Disgust notwithstanding, my bus is there right now, as there are few other options.

[Ray Davis]

Bryan,

Give me a buzz (949-463-0707). We have a new service option in Southern CA who actually wants our business, and according to Steve Bennett is doing a much better job.

Ray

[mike kerley]

Prevost Jacksonville changed all of ours last year. We have full travel front and rear. Only issue was they twisted an airline going to a tag bag and cut the air to it. It was several weeks before I even noticed and the line does not seem to have been damaged and the bag fills normally now.

I guess every repair and technician is different.

[grantracy]

Checked my invoice from Prevost..heres what it says:

2 - #630151 AIR SPRING 12 IN. W/TANK
2 - #630259 AIR SPRING
4 - #630260 AIR SPRING ASSY

Apparently they threw in the air leaks for nothing. Any thoughts? I am unfortunately around 700 miles from the coach so I can't check ride height.

[Jon Wehrenberg]

Gran,

This is not a crisis. We should measure it in OKC and compare it to other coaches. If it does not raise to the maximum height Bill Jensen can address that.

Since you have IFS and slides I would like to see how your lift compares to other IFS, with no slides with the 630259 (front air bags)

[phorner]

Granvil,

Those are the same part numbers for the air bags that were used on our bus when we replaced the air bags.

Everything appears to be operating OK, but I didn't actually measure the lift of the old bags before ours were changed.

[Jon Wehrenberg]

Prevost has adopted the position that the coach was supplied with the correct air bags, and that if Prevost supplies the correct air bags when replacing them if the coach does not rise to the full design height, then the problem is not with Prevost, but the converter who exceeded the axle weight limits.

I fully support Prevost's position on this. As far back as 1990 or 1991 Prevost made it clear that the axle weight limits were critical and must be observed. They went further to state the responsibility lies with the converter or owners who load the bus so as to exceed limits. There position is important and correct because everything from bearings to brakes to wheels and tires are designed to handle specific loads. Exceeding those limits could cause premature failure, dangerous handling, compromised braking, and problems such as the leveling problems.

However, this discussion which is intended to take place at OKC is not to address coaches that exceed the Prevost limits, but to discuss the loss of utility on the coaches which are not in excess of limits and which have previously operated within the full range of operating heights.

For anyone experiencing problems associated with air bag replacement and compromised suspension travel as a result, please bring whatever data you can to the discussion. For example, make sure you have you axle weights, both the actual and the Prevost limits from the data plate. If you had full travel prior to air bag replacement and know how high the coach would go, please state that and relate that to the new maximum height.

Even if you now have the problem resolved, please bring a list of the part numbers of the air bags involved. This will help all of us learn if this issue is easily resolved.

This issue will not go away unless we can demonstrate that coaches within axle weight limits are now not leveling properly. Bring all the data you can find to support those experiencing the problem, including your model year and serial number so we can see the extent ot the problem.

For this discussion we need to be prepared to present facts. Can someone volunteer to gather data at the rally. Email me or PM to discuss.

[phorner]

Jon,

Good idea. Data collection can be very valuable.

Would there be any benefit to having someone receive the info from various owners and compile the data in an Excel spreadsheet or some other tabular form?

[Jon Wehrenberg]

Paul,

Any format that can be distributed would be an excellent idea. I sense we owners are going to be on our own regarding this issue unless we can prove by our data and numbers of affected owners that coaches within the weight limits are not operating as intended and that Prevost needs to address this issue and make it go away.

In the absence of a favorable response from Prevost I would urge we use the information to gather listings of suitable air bags from other sources, including service facilities that will change them for those owners that choose to not do the work themselves.

[bluevost]

Good morning POGgers,

The following comments relate to my (all) solid axle coach vintage 1994 chassis.

Since returning from OKC I have done some reseach regarding original air bags and the replacements called out by Prevost. The original bag was Goodyear 1R11-096 (Prevost #63-0126), no longer available from Goodyear. See the link below to view the spec sheet.

http://www.truckcomponentsonline.com/AIR-SPRING--ROLLING-LOBE--1R11-096_p_1157.html

Prevost is now installing Goodyear 1R11-244 (Prevost #63-0259) as replacements. The above link will get you to the spec sheet for this bag also, use the search tool. One important thing to know is that when looking at the bag from above, the air fitting and the stud are at the 3 and 9 o'clock position. When flipping the bag upside down, the bottom studs are at the 12 and 6 o'clock position. This is key. Although the spec sheet for the 1R11-244 shows the bottom studs at 3 and 9 o'clock, they come at 12 and 6, so I'm told.

Now to the issue of front end lift. As I have stated earlier, I have not been able to lift the front of the bus enough to get level even in a campground, since the air bag swap. Why?? The spec sheets show the exact same amount of travel for both bags. To make a long story short, IT ISN'T THE BAGS. It's our old friend Norgren. That's right. At Mira Loma yesterday, Luis replaced the Norgren valve between the front wheels, and the smaller Norgren on the bulkhead in the bottom compartment. Both of them were original to the '94 chassis. Now I have 7 inches of lift from ride heigth. It must of been coincidental between the air bag swap (Mar. 2008) and the Norgren valve starting to fail.

My apologies to Bill Jensen of Prevost. I put a "chop block" on him at OKC. But he was right all along. I am satisfied that this is the correct replacement bag for my coach.

Ken

[Sid Tuls]

Hey Good morning Ken, Glad to hear about the good comments @ Mira Loma:D I was there last week to replace both of my windshields and have a level 2 service done. I've been very pleased with their work. Scott who also is a POG member is always ready to answer any questons that I have and believe me I always have some. I also dont do any of my own work but feel much better when they put my bus up on the lift and take a look under it with a mechanic. They can spot things that I would miss anyway.

[BrianE]

Hi Ken, Glad your lift issue has been resolved. The way I understand the confusion concerning correct airbag application however never did lie with Bill Jensen or any of the tech support staff. When the 126 bag was discontinued there was an initial discrepancy in the parts department between airbag part numbers and their application to bus serial numbers. The issue has been resolved due in part to input from customers and the willingness of Prevost tech support to listen and have the discrepancy corrected.

[rickdesilva]

Ken
Its great that you figured out the problem. You wire brushed Bill pretty good at the seminar. Its a great feeling when you can figure out one of those irritating problems. For safety I would just keep Buster away from your coach.....unless he's serving cocktails.

[Jon Wehrenberg]

Ken,

Can you please be more specific as to the Norgren problem. This is an apples and oranges situation so we need to clarify how an owner can determine if he has an air bag issue or one related to valving.

As I read your post I was led to believe you could raise your coach to the ride height manually, but not beyond. That would be an air bag issue. But if what you are saying is you cannot raise your front at all, except by going to the driving or ride position, then it is an issue related to the Norgren valves.

Do I have your issue properly interpreted?

[bluevost]

Jon,

It seems air pressure was the issue. There was enough (barely) to raise the front of the bus to ride height, but not enough to raise the bus for leveling. Luis mentioned a build up of moisture over time could have been the culprit. The Norgren valve had no problem dumping air, but would not let enough air pressure pass to raise the bus. Does that make sense to you??

Ken

[Jon Wehrenberg]

Ken and others reading this:

If the opening in the Norgren was only big enough to allow one molecule at a time to pass through it, given enough time the air pressure of the air bags would eventually equal the air system pressure.

I surmise the Norgren was in fact capable of opening to allow air to pass in sufficient amounts so the bus was able to come all the way up to its fully extended height within a reasonable period of time. I further surmise Ken was either impatient (I doubt that) or there was a real problem which we will now never know.

When the bus is asked to rise fully on the front axle two of the solenoids on the rear steer compartment are energized and the air flowing through them (one of them anyway) shifts the Norgren valve from being closed to opening a path from the aux system pressure to the air bag. I will agree if it does not open fully a smaller volume of air will flow through the Norgren per minute, but at some point the air in the air bags will equal aux system pressure and the front air bags will be fully extended. I never heard Ken say the bus would go beyond ride height.

If the five port Norgren does not open then nothing happens. It will not even come up to ride height. My guess to explain the issue is one side of the Norgren may have been water logged and it created a hydraulic lock preventing the Norgen from functioning in the manual direction. It obviously shifted and opened in the direction that brought the ride height valves in play.

A water logged valve likely is corroded so replacement is a correct recommendation. That water logging comes from a failure to drain and maintain the air system on the bus, a situation made worse on the aux air side.

Now to play devil's advocate.......that does not explain why many others are having problems getting their coaches to the fully raised height. I doubt that all are the result of a bad Norgren or bad solenoid valves. This may be a mystery we cannot ever solve unless we knew precisely what happened when the controls were set to raise the front and exactly what parts Prevost changed to make the front raise.

Just so everyone is very clear on this, our air bags will raise in proportion to the amount of air pressure in the bags. If the section of the coach to be raised has more weight then the air bags will need more pressure than a similar coach that has less weight in the same area. The only thing that will allow a coach to raise with lower pressure is a larger diameter air bag.

If a coach needs to come up to its fully raised position it will do so as long as two conditions are met. First, there has to be a flow path. If the valve fully opens then air can flow faster and the pressure will rise quicker and the coach will come to its fully extended height. If the valve only partially opens, no matter how small the aperature, it will still come to the fully extended height, only it will take longer for that to occur.

As a reference point, my front air bags will fully extend if my system pressure is around 110 PSI, and they will be at ride height somewhere around 100 PSI. The rears take less pressure to fully extend. Any pressures above what it takes to get full extension is excess. Someday I am going to set up a means to monitor air bag pressures just for information gathering purposes.

[Ray Davis]

Given that the way you raise a bag is to select with the Level-Low and then manually press and hold the UP switch, it's most likely that this was only done for a few seconds, to maybe 20 seconds or so?

So, IF the Norgren was indeed slow, then this would give the symptom of not being able to rise above ride height?

Ray

[gmcbuffalo]

How can we check our sluggist noregen systems to eliminate the possiblility of water logging? Is this a matter of disconnecting a air line and letting air blow out?
GregM

[Jon Wehrenberg]

Moisture can enter our bus brake and auxiliary air systems via humidity in the air compressed by the engine driven compressor.

To prevent that moisture laden air from getting beyond the first compressed air tank we must maintain the dryer element. As long as the dessicant in the air dryer is maintained it traps moisture and what little oil passes the compressor. If any moisture and oil passes the dryer it is supposed to be captured in the first compressed air tank in the system referred to as the "wet" tank.

Coming from the other direction, the auxiliary air compressor can also introduce moisture into the system. Most coaches are equipped with some form of moisture trap to catch this moisture. The aux air supply will not introduce air or moisture into the braking portions of the air system. Both the engine driven compressor and the aux compressor can and do introduce air and moisture into the aux system so maintenance of the air system is the only way to prevent moisture from collecting in amounts capable of creating a hydraulic lock on the Norgrens or corroding the interior smooth surfaces of the valves.

Maintenance consists of replacing the air dryer cartridge or element as often as necessary. Generally when moisture is seen in the wet tank along with some oil contamination in a higher than normal quantity it is time to change the element. I change mine every two years, but someone using the coach more often or in high humidity conditions or whose compressor is passing some oil may need more frequent changes.

The next step in maintenance is to drain all pressure in all tanks draining all moisture out at that time and checking to insure each tank in series maintains pressure to verify the system check and protection valves are functioning as intended.

The final step is draining the aux system water trap.

I drain my tanks every 5000 to 6000 miles and so far I get very little moisture from them. Perhaps I collect a table spoon or two, total.

If sufficient moisture has collected in the suspension system valves I suspect they can be drained by removing every hose or fitting, but I also suspect the moisture has corroded the valves so they will leak and the bus will get the leans. It is a whole lot easier and cheaper to maintain the air system in our buses than it is to try to reverse the problems trapped moisture and cause. For those who operate in sub freezing temperatures moisture in the brake or aux systems can create major problems.

[bluevost]

Jon,

Thanks for the great explanation. Let me first say that patience is NOT one of my spiritual gifts. This is an ongoing struggle.

My conversation with Luis included moisture from the aux air system. My small aux air compressor has no dryer, probably like most of our coaches. He taught / showed me where to drain this system. Most likely when I tried to raise my bus' front end, I did not notice any change because the air way was mostly blocked, and I did not hold the UP switch long enough.

BTW we can camp without the aux air compressor on, because of manual pocket doors, electric toilet, etc. The only time I run it is before starting the engine to bring up the small air bag on the belts. And I have never drained it since we owned the bus (4 years next month). But I will now!!

Ken

[truk4u]

Just to expand a little on Jon's point, while I had the 2000 CC, there was a button in the front bay for purging the aux air compressor tank of water. The CC has it's own aux air tank and almost every time I purged (often) there was moisture coming out. The aux compressor will for sure put moisture in your aux tank.

For most of us, our aux compressor feeds directly to the aux tank and the only place to drain moisture is the tank itself and the filter in the steering bay. Some of them look like this with a drain on the bottom:

5831

[phorner]

One caution regarding that Norgren filter in the steering bay. If you open the valve at the bottom to drain it, there is a very good risk of creating an air leak at the valve. The drain valve is kind of crappy and I've had aux air leaks there that simply refused to be corrected.

I have since replaced the whole lower assembly and now, when I drain this filter, I simply remove this lower section to empty it rather than touch the drain valve. I just wipe the inside with a paper towel. The down side is that you can't do this under air pressure.

If you have an assembly with a leaking valve, it looks like the old valve could be removed, the body tapped with 1/4" pipe thread, and a new brass valve installed, but I haven't tried it.