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 Specifically we got 630126 air bags for the front axle of our coaches (now superceded by 630259) and not the air bags listed on the bill of material.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.

[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.
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[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.