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 Specifically we got 630126 air bags for the front axle of our coaches (now superceded by 630259) and not the air bags listed on the bill of material.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