Air Springs Revisited

[BrianE]

Since the "Replacement Air Springs" thread seemed to end up with severe creep and since the issue didn't seem to come to a consensus here is a little fresh info on the subject.

While visiting Prevost Mira Loma last week I started asking questions about how current airbag replacements didn't seem to perform as well as the old 630126 (Goodyear 1R11-096) "Maywest" springs. The replacement for the 126 is indeed the 630259 (Goodyear 1R11-244). Comparing the specs of the two on Goodyear's tech site shows their specs are identical. There is a difference however in the airsleeve (rubber) part number they use which may have been why the 126 seemed to work better. Coincidental with the discontinuation of the 126 Prevost offered a (surprise) OPTIONAL airbag for entertainer coaches and motor homes. This bag is PN 630151 (Goodyear 1R12-377). This bag is manufactured exclusively for Prevost, consequently Goodyear tech support wasn't willing to divulge its' specs. The bag is a 12" diameter bag however vs 11" for the 259 and you can see from the photo, is about 1" taller than the 259. We can probably assume that when Joe and probably others have ordered new bags from Prevost, they weren't informed these optional bags were available. Hopefully someone will be ordering new front bags in the near future and will be able to report on their performance. Assuming their extended height is 1" higher than the 259 bags and their diameter is 1" greater, an increased volume of about 130cu in is gained with the optional bags. Should make quite a difference

[Petervs]

Brian,

When I was young I learned that anything more than a handful was wasted.....

[Joe Cannarozzi]

Thats prefect. Now they added another choice.

Brian how did you get those pictures?

All the buses I put the 63-0259 resolved issues and preformed wonderfuly.

So now the stock bag is the 63-0259 and the new mae west is the 63-0151????????

[dreamchasers]

Brain,

Thanks for the details. I will be one that replaces my front air bags before the Oklahoma rally. So additional information is forthcoming.

Your discovery certainly explains the airbag issue. Good info!

Thanks,

Hector

[truk4u]

Wow, the Mole Man comes through with some really good stuff. Thanks for the research Brian and this may help with some of the whimpy front end lifting. Don't forget to adjust your ride height boys!

[gmcbuffalo]

With the extra 1" in diameter will we have any rubbing issues?
GregM

[Joe Cannarozzi]

I have never been given that # from anyone at Elgin nor have they ever sent that bag to any motor home owners that have had parts ordered ahead of time and Mr. Jenson never mentioned that bag when he informed me they were not responsible for sending bags that wouldn't raise the front on a motor home.

Brian do you have the name of the fellow you spoke with?

[Jon Wehrenberg]

Brian has just revealed the truth..........

Lets assume the 259 is indeed a direct replacement for the 126. Assuming their diameter and height dimensions are identical they should lift the front end of the bus easily. Using the 11" diameter as the effective lifting area the air bags have a 95 square inch lifting surface. The lifting surface area determines how capable an air bag is at raising or supporting the weight placed upon it. In the case of the 259 and 126 this translates into an ability to support 9500 pounds per air bag at 100 PSI. This is theoretical because we do not know the actual lifting area, but is good for analysis.

The entertainer air bag 630151 has a 12 inch diameter. That additional 1" of diameter does not seem like a lot, but it calculates to 113" of lifting surface, or one that is capable of supporting 11,300 pounds at 100 PSI.

Stated another way, the 259 requires 73 PSI to support my coaches front end weight and the 151 requires 62 PSI to accomplish the same thing.

Again, these numbers are bogus, but serve to illustrate how increasing the diameter has a huge impact on the pressure required to lift and support our coaches. Before the mad rush to replace front axle air bags however there is a need to consider the impact of using a larger air bag. If the air bags now in use work, that is they support the coach and allow you to raise it to the maximum height you may not want to make changes. Like a lot of things on our coach the sizes of components has been decided after a lot of factors have been taken into consideration. Air bags are one of those things that require a lot of consideration.

Apart from space considerations, making sure a larger diameter will not rub on anything, a larger diameter should only be used if the axle weight is substantially greater than normal. Entertainer coaches certainly meet that criteria. The longer wheelbase and the substantially reduced rear overhang places a greater load on the front axle than the typical motorhome conversion. That increased front axle load will require a greater internal pressure for an air bag that has a 100 PSI limitation branded right into the sidewall of the air bag. Entertainer coaches need the greater diameter to keep the pressure within an acceptable range.

So what happens if you place bigger diameter air bags in your coach? Depending on the front axle weight, you could end up with a coach that mushes down the road, that dips dangerously on hard stops, and that leans excessively in turns. With a substantially lower internal pressure the ride will go from firm to very soft. Does anyone remember how poor the classic cars used to handle with their soft ride? The cars of today have a much more tightly controlled ride and as a result their handling is very good. The same is true of our coaches.

I'm all in favor of changing air bags on a coach that struggles to reach ride height or which has a hard time extending to full height. That tells me the air bags are likely overworked and may benefit from a change in size. But if the coach does not struggle and you do not have to do special things like lifting a tag axle to raise the front, I would suggest staying with the 126 or 259.

As far as extra height, as long as an air bag has greater lift than 4" available at its installed height of around 11" it is more than a handful and is not necessary.

[Kevin Erion]

I guess I got lucky, maybe not if you go with Jon's statement about if you need the extra capacity to lift. I replaced all my air bags about 3 weeks ago and the ones I received from Mira Loma for the front are the 630151 bags. I will take the bus for it's first trip to Havasu this weekend after the replacement and report if there is any difference in ride quality. I am afraid that because it has been about 4 months from the last use I won't notice anything, I am hoping that's the case anyway!

[phorner]

For what it's worth, when Prevost replaced my front air bags (1999 IFS shell) they used the 630151 12" air bags.