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.

[Jon Wehrenberg]

A little bit of apples and oranges. The geometry of the IFS which Paul and Kevin have cannot be compared to the issues that Eric and Deb had for example unless the IFS coaches have no more or less mechanical advantage in supporting or lifting the coach. This issue makes me want to put gauges on my suspension system just so I know the values of the pressures required to go from full down, to ride height to full up.

In Kevin's case I'd bet his coach will ride and handle closer to what the engineer's designed because Marathon conversions tend to be a little (or a lot) front heavy. Paul likely has a softer ride. I don't think either is dangerous as long as the shocks are in good shape because they tend to dampen the mushiness.

[Denny]

Ditto to Paul's post. Joe recently replaced my air bags etc, and Prevost sent 630151 12" air springs

[lonesome george]

Here is a foot note to Jon's reply.
Our old coach was a Beaver Patriot with a Maginum chassis and the front suspension was harsh on small amounts of suspension travel, it had a regulator mounted under the body near the height control valve, not user friendly and not ment to be and no gauge. We installed a gauge to check the pressure and it was about 60 psi. I removed the whole thing and ordered a non-relieving regualtor and gauge, mounted it in the storage bay so it could be adjusted easily. Turned out it took about 35-36 psi to lift the chassis at all, at 40 psi it would come up about as fast as it did at 60 psi. The improvement in ride qaulity at 40 psi was remarkable and I did not find any change in body roll or increased bump travel on hard braking. Did the same thing on the rear but could only drop the pressure about 5 psi from the OEM set-up.
This may not work on a Prevost, for one thing it takes our's several minutes to lift it's self up after being lowered, so I think the pressures on a Prevost maybe very close to the minium pressure to lift the coach, the Maginum has 4 air spring on each axle so it is a different beast..
It was a fun project that had a good result.

[Jon Wehrenberg]

There has been confusion in the past on air bags, pressures, ride height valves, etc.

When in the road or driving position there is no way to regulate air pressure in a set of Prevost air bags to adjust the quality of the ride. The air pressure in our air bags is controlled solely by the ride height valves, and each valve controls its respective set of air bags.

All ride height valves function exactly the same. A lever arm from the valve (which is fixed to the bus body) is attached to a portion of the suspension, such as the front axle or the rear drive axle carrier. When the bus is sitting in its lowest position and the suspension system control is placed in the road or drive position, the arm which has been pivoted up because the bus body is down relative to the normal ride height opens the ride height valve to admit air to the air bags.

As air enters the air bags the pressure inside the air bags increases until the air bags begin to lift the bus body. When the bus body has risen to the normal driving height, the lever arm on the valve body is centered in its range of travel and the flow of air into the air bags stops. Whatever the resultant pressure inside the air bags is what it takes to support the bus body at the normal driven height. That pressure varies with circumstances. An empty bus will have less pressure inside the air bags at a given height. A bus with 45 fat people will require a greater pressure to place the bus at its driven height. And when those fat people get off the bus, the pressure in the air bags is in excess of what is needed and the body will rise as a result. But as the lever arm on the ride height valve is lowered because the increased air pressure is lifting the bus relative to the suspension, the ride height valve begins to bleed off excess air pressure until the bus is restored to the correct driving height.

Our buses will not have 45 fat passengers. our weights are somewhat constant if you ignore our fuel and water consumption. But our ride height valves are still working as we drive. Going around a wide sweeping curve will make the bus start to tip due to centrifugal force. As the bus begins to lean the outside (of the turn) ride height valve admits air into the air bags on that side and the inside ride height valve exhausts air keeping the bus distance from the road equal side to side.

The only time we have the ability to exercise any control over the air pressure in out air bags is when we level our buses at a campsite. Even then we are more concerned with how high or low we need to make a certain point on the bus as opposed to how much pressure do we need in each air bag.

We have air regulators on the bus for various purposes such as belt tensioning, but our suspension system itself has no pressure regulators, only valves which open to admit air or exhaust air to the air bags as required by circumstances.

Think of the ride height valves as a three way switch. In one position it opens the flow of air into the air bags. In the center position it is the neutral position and air is neither flowing in or out of the air bags. This is the position the valve arm is in almost all the time we are driving. The remaining position allows air in the air bag to be exhausted from the air bags.

[phorner]

So, what's the rationale for an IFS chassis, that is still a MH chassis, to have the larger front air bags than a non-IFS bus that's only a couple of years older?

I can understand the difference when applied to entertainer vs motorhome applications, but apparently there is some reason that Prevost went to the 12" front bags for the use in motorhomes?

The more I think I understand, the more confused I get :eek:

[BrianE]

Joe, As you can see from Kevin and Paul, the 151 bags are being used as replacements. I initially spoke to Donavan Pelky, a parts team leader in Mira Loma and he told me about the 151. I then looked in my own Catbase Prevost Parts program and confirmed they are an option so consequently should fit without rubbing issues. I also spoke to Charlie an old time parts pro in Chicago because I wanted to get specs on the 151. As far as I know the actual specs are not available from Prevost. The diameter is of course 1" larger, the relaxed height is about 1" higher, the only unknown is the fully extended height. It can be assumed that height is somewhat more than the 259. As to ride height concerns, the ride height valve doesn't care what bags are installed, the ride height won't change as long as any airbag is capable of reaching ride height.

[Jon Wehrenberg]

So, what's the rationale for an IFS chassis, that is still a MH chassis, to have the larger front air bags than a non-IFS bus that's only a couple of years older?

I can understand the difference when applied to entertainer vs motorhome applications, but apparently there is some reason that Prevost went to the 12" front bags for the use in motorhomes?

The more I think I understand, the more confused I get :eek:

To rephrase it another way Paul, why would Prevost want to carry extra inventory? If the 151 is deemed by the Prevost engineers to work in all applications, why bother with the 259?

There must be a reason why that is listed as the standard, but as Joe learned trying to get information is not easy.

[lonesome george]

Jon,
From your explanation it seems to me all I did with the Beaver is slow down the reaction time, which may have been why it had a regulator in the circuit in the first place.

[Joe Cannarozzi]

Brian did he say the 151's could be used on a straight axle non-entertainer, specifically?

The bases are slightly different.

I agree with Jon. Every straight axle I put the 159's on easily brings the front all the way up at idle, compressor not running.

[Jon Wehrenberg]

George,

Without looking at the Beaver system it would not be possible to determine the function of the pressure regulator.

Slowing or speeding the process of adding or exhausting air from the air bags is something Prevost does on older coaches using a time delay ride height valve, but they have gotten away from that and now use instant reaction valves. They will also supply the instant acting valves as replacements for the time delay ride height valves.

If Beaver used a regulator to slow down the reaction time they could have saved lots of money by just using a valve in line to function like a faucet, opening or closing it as required to regulate the flow of air.

[PartsSurfer]

Joe,
If you would like some help with the airbag situation, please feel free to give me a call. I actually had a really good time trying to help Mr. Esler figure it all out. In fact, I would love to hear from any of you who have motorhome specific questions. I spent some time with Marathon Coach,Country Coach, and Monaco.
We are also lucky enough to have a considerable amount of experience in the shop right out my window. If I don't know the answer, I'll find someone who does!

[Joe Cannarozzi]

That's great I will almost definitely take you up on that.

I did air bags on 3 buses that Prevo sent 36-0260 for the fronts before we realized they were wrong. The first two buses had computerized leveling and so we did not try to manually raise the front higher than ride height.

It wasn't until I installed them on that first bus with the stock Prevo level-low, while manually exercising up and down after installation, that we figured out they would not raise the front higher than normal ride height.

We have since been installing the 0259 and everything I put them on works great:)

Brian posted another part# 0151 maybe? Anyway, can those be used on straight axles? I have put those on IFS but never a straight axle.

It is probably safe to refer to Mr. Esler as Brian around here;)


Our chassis is a very late 84 and we do not have Norgrens. The tag axle has a 3-port valve that is configured similar to a 3-port norgren but it is a diaphragm type valve and it is in the resting position "tag-up" so it needs accessory air to keep it down. I have been looking at the conversion schematics to change it over and it looks unnecessarily overcomplicated. I know that when you raise that axle it shuts off the brakes too but I still think there is a simpler way to plumb it.

I have oodles and oodles of used Norgren valves I need to get some rebuild kits get these bench tested get under there and see what I can come up with.

[Gary & Peggy Stevens]

I would like an answer please, that I don't remember seeing in any of the posts before.

When I put my bus away to get it in the door I have to remove all air from the suspension..... I leave it this way, all though once in the barn I could raise it back up.

My question is:

"Is it ok to leave the bus sitting down on the empty air bags for extended stays or should I refill with air, and then drain the air again before I pull the bus out of the barn?"

Thanks.

Gary S.

[Jon Wehrenberg]

Gary,

I believe our air bags have internal rubber bump stops in the base so when the bus is all the way down that is what is supporting the chassis.

Except when I have it up on stands for servicing, I drop it all the way down and have done so for as long as we have owned a coach. If it hurts anything i am unaware of it.

I also have to lower the front all the way down to get it in the garage and after getting the first 10 feet out of the garage I have to raise the front all the way up. If exercising the air bags is bad I am not aware why.

[tdelorme]

You aren't hurting anything leaving the bags deflated. I once left our Foretravel sitting for two years with the bags empty. When we started using the coach again, the bags were fine. The tires and 200 gals. of diesel were good to go as well. I had dumped in a couple of gallons of Howes Diesel Treatment in the tank after I realized the coach was going to be in one spot for such an extended period of time. How come you guys built bus barns with low clearance??

[Jon Wehrenberg]

My bus barn is perfect for a 40 foot coach. Just back it right in. Never planned on having any other coach until the fire changed all that.

But when the mirrors on a 45 foot coach are still lower than the floor level when backing up the hill into the barn that presents all kinds of problems.

You will just have to take my word for it.

[Joe Cannarozzi]

Ask and you shall receive.

Once upon a time air bags had removable reusable tops. Here is the bottom of one of those and the rubber bumper that is attached to it, that the bus comes to rest on when you dump all the air.
4176

Somewhere after 95 but before 98 they increased the diameter to the air inlet from 3/8 to 3/4in
4177

This is what happens when the Horners talk you into getting under their bus and you let Janice go unsupervised with the camera.:eek:
4178
You have never done a really dirty job till you have had to rinse off with gasoline:rolleyes:

[phorner]

Joe, I can't believe you posted that picture :D

Ya know, I never had much fun that kept me from getting dirty :)

Being back at TGO last week sure brought back a lot of good memories.....such as this picture....

[Jon Wehrenberg]

I am sorry to inform Joe that his application for the Prevost Prouds has been turned down.

[PartsSurfer]

Joe,

I'll try to nail everything in one reply:
630151 is only an option on the Independent suspension.

I'm working on trying to find rebuild parts for the Norgrens (haven't tried tackling that one before), and I spoke with a Tech who just completed the burkett to norgren retro and got some scoop. I'll be here at the office the rest of the week, so if you get a chance, give me a call. 951-360-2550.

I'm working on an article that should help explain in lamens terms(or parts guy terms, whichever you prefer) the conversion process. Will update soon on the norgrens.

And I agree completely that they called the race at Daytona too soon. I can't believe Kenseth cried. Sheesh....

[truk4u]

Parts Dude,

There's no crying in Nascar, I couldn't believe it either!:o

[Jon Wehrenberg]

Parts Guy,

I assume you are with Prevost so you have access to substitutions and pieces and parts not found in our parts books. So far, to the best of my knowledge Joe is the only guy in POG that has a coach with those valves. If you want to really have a good impact on POG folks, outline the changes required to stop the older coaches from dumping tag axle air when the aux pressure drops below a certain value. There are several on this forum that would likely spring for the fix.

[truk4u]

Excellent suggestion Jon.... I believe the Prevost part number for the kit is
9614A, Reverse Tag Logic, but I don't see it on the parts list. I for one want to do this fix asap.

[Joe Cannarozzi]

Jon it seems like there may be only 1 conversion regardless of the vintage. We will see. Hector already posted it somewhere.

[dreamchasers]

Here is the thread that addresses the kit available for coaches older than 1995 - 1996. Mine is a 1995 and the suspension logic will release on low aux air pressure.

http://forum.prevostownersgroup.com/showthread.php?t=2685

In post #7 is a link for the Prevost instruction for the upgrade and in post #16 is the price I was quoted.

I would be interested in hearing of the results of anyone that attempts to install this upgrade. I decided to keep my aux air system 'tight'.

Hector