Air Bag Ride Height Dimension - 259 Bag

[truk4u]

Anyone have the measurement for the bags on an XL, I can't find it? The measurement is from the top plate to the bottom plate I think.

[JIM CHALOUPKA]

Tom, I think if you call Prevo parts the salesman can tell you that dim.

JIM;):D

[dale farley]

Tom,

On page 16-29 of my maintenance manual, it says the measurement for the front air bag is 11.7 inches at normal operating air pressure of 95-125 psI. The measurement is from the top to the bottom of the plates.

The rear bag measurement should be 11.5 +- .25". Hope this helps.

[Jon Wehrenberg]

Dale,

Don't confuse air bag measurments with the Prevost recommended ride height measurements.

The dimensions you cite I think are the dimensions you wish to obtain when adjusting the ride height valve arms. That dimension can be adjusted up or down, but what Prevost specifies is what they want the ride height to be.

The air bags will actually extend to a greater height, limited only by the shock absorber travel and dependent upon aux system pressure.

[truk4u]

What I'm trying to do is make sure my ride height is within spec. After replacing my travel coil/valve, the bus now seems to be setting too high and changing those components should have no effect on ride height (measured from the bottom of the bus just behind the front wheels and just in front of the rear wheels). The air bags are right at 12" when measured from top plate to bottom plate and the ride height is 11 1/2" measured from the bottom of the stainless to the floor as mentioned above.

So which measurement is the real ride height number Jon Boy?

Thanks Dale, I don't have the Prevost maintenance manual unless Brian hid it.

[dale farley]

Tom,

My scanner is not working, so I made pictures from the maintenance manual.

[Jon Wehrenberg]

Tom,

Dale has it nailed. You are 3/10 of an inch too high, but that is less than 5/16" and I seriously doubt if you should monkey with that. The reason I say that is that there is a range of repeatability in the ride height valves. If you cycle the bus up several times and then go to the drive position and take measurements, and then cycle the bus down several times and return to the drive position and take measurments it is probable you will find a variation in those dimensions. If they are consistently high or low you can probably make an adjustment to bring it closer on average, but you will never be able to eliminate variations due to how the ride height valve works and even a little slop in the arm will have an effect.

[truk4u]

Jon,

I've moved it up and down full travel several times and it does get pretty close each time, but your correct, there is a little variation. I think I'm good and when I bounce it down the road to Florida in Nov, I suspect there will be slight changes.

I'm going to record the height on each side from the stainless to the pavement and that would be a an easy reference for checking the height in the future without dealing with air bag measurements. I did that on the previous buses, but now have CRS!:o

For anyone playing with this ride height stuff, you have to keep up a good supply of aux air if your not running the engine. I attach shop air to the aux tank, then I can just stand outside the steering bay with the drivers window open and play with the level low buttons. This is strictly for measuring the body ride height and no underneath work! Never get under one without full blocking and bracing that has been discussed a gazillion times.

[dale farley]

Tom/Jon,

I was playing with mine last week, measuring from the stainless to the floor. I was running my engine and would let the bus auto level at various heights then return to ride height. I noticed slight variations in the measurements. I am glad to hear the variations are normal.

[Jon Wehrenberg]

THIS IS IN CAPS BECAUSE OF THE IMPORTANCE. TOM IS ABSOLUTELY CORRECT ABOUT NEVER GETTING UNDER THE BUS UNLESS IT IS SUPPORTED

ESPECIALLY IF YOU ARE MESSING WITH THE SUSPENSION VALVING

There are two types of ride height valves now installed on our coaches. One is instant acting (newer chassis models or those that have been changed) and the time delay ride height valves typically installed on older chassis.

If the coach is not supported, you can get surprised when monkeying around with ride height valves. Ironically, when adjusting the valves you need to allow the bus to go up or down so you can see the impact of adjustments that you make to the valve arm. My advice is to either get the bus over a pit so it can freely move up or down without putting you in a compromising position, or put it up on ramps, or verify you are in the wheel wells and will be unaffected if the chassis goes up or down.

[GDeen]

Tom, and anyone missing the paper manual for the chassis, this information is also contained in the link below which I provided in another thread.

http://prevostparts.volvo.com/technicalpublications/en/manuel.asp

Download the "air system and suspension" manual under maintenance and it has the same info as what Dale provided.

[truk4u]

Gordon,

Thanks, but no PNEUMATIC DIAGRAMS for my vintage.

[Jon Wehrenberg]

Actually, I don't think air was invented yet when your bus was built.

[truk4u]

A Liberty owner bashing a Liberty owner, the shame!:rolleyes:

[GDeen]

Gordon,

Thanks, but no PNEUMATIC DIAGRAMS for my vintage.

Following is for 89 - 2000 model years which seems to have you covered

http://prevostparts.volvo.com/technicalpublications/pdf/pa1082-16.pdf

Document Title:


Number Manual Section Vehicle Type XL BUS, XL
PA-1082 1989-2000
16 - Suspension
16 - Coaches Equipped with Independent Front Suspension
16 - MTH Equipped with Independent Front Suspension

Page 10 has the same specs as Dale produced from his paper manual....Edit - actually says 11.5 for all 4 corners.

[phorner]

I fired up the bus yesterday (since I had the engine nice and toasty having had the Webasto on the night before) and the bus failed to achieve ride height.

The right rear air bags don't respond to the "Road" position. I can raise or lower the entire bus manually. However, the right rear corner will stay at whatever level it is placed in manually when switched to "road".

Comments??

[JIM CHALOUPKA]

Paul, sorry you're having trouble getting it up.

:DJIM

[dreamchasers]

I fired up the bus yesterday (since I had the engine nice and toasty having had the Webasto on the night before) and the bus failed to achieve ride height.

The right rear air bags don't respond to the "Road" position. I can raise or lower the entire bus manually. However, the right rear corner will stay at whatever level it is placed in manually when switched to "road".

Comments??

Paul,

Suspension issues are almost impossible to correctly diagnose on the forum, but visit the multimedia suspension presentation (link below). This should add a little clarity. It looks to me, with your described symptoms, either a Norgren or a ride height valve is not functioning correctly. I would look at the ride height valve first. The ride height valve is located behind the rubber flap, forward of the dual axle. You can look up under and see if the the link to the ride height has come loose. Always have you coach suspension supported before crawling underneath.

Log on the suspension overview a take a look.

http://forum.prevostownersgroup.com/showthread.php?t=2116&highlight=airbags

Hector

[phorner]

Thanks Hector,

My first inclination was the right-rear ride height valve, since the left side is apparently working OK.

Confounding me is that both rear ride height valves are only about a year old, so I am kind of surprised to see a problem there.

[mike kerley]

Paul, I'd dump all of the air and start over with achieving ride height. Do it several times. Most likely a valve stuck from the cold. Cycle them all several times and I'll bet it comes back...

[Jon Wehrenberg]

Paul, The advice so far has been good. Here are some ideas that might be part or all of your problem.

First, if the five port norgren is not shifting it will have that problem. I have ruled out the solenoid valve because the front and other side are working so corrosion or a lazy 5 port norgren can be the issue. Try exercising it by seeing if you can raise or lower the side in question using the manual position and then go back to the road position.

One cause for what you describe that a lot of folks overlook is related to the road height valves. The arm position controls the operation of the valve, but it the arm passes its extreme limits no air will flow through the valve in either direction. I am not familiar with the instant response valves you have, but on the delayed respnse valves if the postion of the bus has passed its normal operating range, the only way to restore the valves to functioning is to manually adjust the coach height to get it within the valve operating range.

So you may wish to manually raise the coach a few inches and then see if it will automatially go to road height. The answer is only within the five port norgren and the ride height valve on that side.

[phorner]

I decided to try to "exercise" the system to (A) better document the problem and (B) see if the symptom improves.

It appears that the problem has "self-resolved" which is both good and bad news. Glad everything's working OK but sure wish I knew for sure what the problem was.

I manually raised and lowered the bus to the high and low limits, and then went to ride height from both extremes. Then resumed to ride height after just a little bit too high and a little bit too low. Then back to full travel at both extremes. Then the whole pattern all over again.

One interesting side note: I decided to take measurements as the bus was moving up and down. The front ride height returned to the same constant whether achieving ride height from either full up or full down position.

However, if I dropped down to road ride height after the bus was at the upper height limit, the rear returned to an elevation 1/2" higher than achieving road height by raising from the lowest position.

Of course, this was strictly a static test. I'm guessing that if I drove the bus any distance, the rear ride height would settle out to be the same either way as the ride height valves adjust up and down during travel.

[Jon Wehrenberg]

Paul it was either a lazy 5 port norgren or you were beyond the limit for the ride height valve.

Whatever it was ignore it because whatever it was is gone and exercising the coach will do nothing but good for it.

Some things are not worth worrying about. That's one of them.

[charlesebrownjr]

I need to know if any of you have the correct part # for air bags for a 40' XL CC. My bags are now 10 yrs. old and I will most likely replace them this summer or next fall but I have seen post where everyone says that the bags Prevost wants to use are not the correct ones. Help:eek::eek:

[Steve Bennett]

Paul, you may still want to take a look at the leveling valves. We have seen them get contaminated from oil coming from the compressor. If you look at the port on the bottom of your air dryer, and see a fair amount of oil, or can see any oil on the bottom of the leveling valve ports, that is your likely problem. If the valves get contaminated with oil, they will stick and be slow to respond. Generally replacing the leveling valves, and servicing the dryer will eliminate any future problems. Charles, Prevost has updated their information on the proper air bags. Make sure you provide them with your vin#, and make sure they know it is a motorhome.