Correct Ride Height ?

[Jeff Bayley]

Dear Abby-

It has seemed to me recently that my bus ride height is too low. It hasn't changed, I just started noticing other buses and a lot of them seem to ride higher. I'm CERTAIN that XL II's ride higher (mines a 95 chasis XL). Prevost confirmed that the XL II is indeed higher. I had Prevost check my ride height and they said it was good but I need to get a 2nd opinion. Can you measure from the bottom of a bay door to the ground and what is that supposed to be ?

Also, I finally got the bright idea to raise the coach an inch or two with the level low and just leave it there when I drive and I'm trying to experiment and get a sense if the ride is better or worse and it seems to me to ride a little bit better when I leave it up an little bit. Not too much, just a touch. I'm not hurting anything in my level low by doing this am I ?

[Jon Wehrenberg]

Jeff, I will try to remember to look up the proper height and post it. I seem to recall that the measurement is the airbag height when the coach is in the road position. I have a perfectly flat garage floor so rather than trying to get that dimension I measure from the floor up to the bottom of the bay doors all around. There are other points you could use if you are on perfectly flat ground, such as a body seam.

But let's discuss riding with the level low on. DON"T.

There are so many potential problems with doing that I would urge you to reconsider. There is a reason why your dash has a big red light on when you are in the level low position while you are driving.

You may think you can detect a change in how your coach sits relative to the road when you drive, but you cannot. In the level low position you eliminate the part of the system that maintains your air bag inflation level, and when the air bags are not where specified it has the potential to change your steering geometry (among other things) causing steering control issues.

As long as the air bags remain inflated to the specified height life is good and everything works as intended, but if the coach is too high, too low or leaning it may create problems.

[MangoMike]

Jeff,

You might want to check out this post from stuff.com about ride height.

http://www.prevost-stuff.com/cgi-bin/_ubbcgi/ultimatebb.cgi?ubb=get_topic;f=18;t=000096#000008

Also, although I'm not positive, I think when you're in level low, the 3 ride height valves that help distribute the load are now disconnected. Unless you're trying to traverse something say like Jon's driveway I would stay in ROAD mode.

Keep us posted.
Mike

[dalej]

Jeff this is the bit of info that I have....let your coach down on the ground, or let the air out of the bags. Then start your aux. air and let it run. Turn your key on, but don't start the Detroit. Your bus will air up to to ride height. Measure the distance between the steel plates where the air bags are. This distance is 11 and 1/2 inches. You can preform this with the engine running, it is just loud and you can't hear the valves working. If you need adjustments made, you do so. Note: it is really nice to use aux air. If you don't have it, hook a air compressor to the aux. tank in the steer bay.

[rfoster]

Dale, Your sure have been busy posting the map lately,(keep up the good work) But I need to interrupt and ask --how much pressure does your aux compressor generate in order to lift your coach? Do you know the magic PSI number that works? My Aux Air will not lift it, and I have 110 psi shop air and it will not lift it. I tryed what Truk4u suggested by raising the tag and I may have gotten an inch raise out of the front bags.
The only way for me to lift is with the engine compressor running and when the air gauges on the dash reach about 110 it raises the front.

Does this sound unusual or normal ?

[dalej]

I bought one with 135 pounds, it works great! I had posted photos earilier in some thread.

[dalej]

Jeff, I forgot, use safty blocks when you are going under the bus. Don't block the bus up just keep it from dropping if somthing goes wrong. If you can run the bus on planks at least 4 inches when you work under the coach, it help out. Or better yet just head over to Jons. Having a pit must be the best!

[Jon Wehrenberg]

Dale and mango are definitely on their games. The space as Dale describes is the top of the heavy plate the air spring (air bag) base rests on to the underside of the top plate that the top of the air bag bolts to.

As Mango posted the ride height valves have a small time delay before they react so use extreme caution.

[Jeff Bayley]

Thank you for the feedback.

1) I don't THINK I have an aux compressor but I'm not sure. I've read prior post regarding this and glossed over it thinking I probabley had it but didn't know for sure but I just now realized that what I see that make me think I might have that is an "Aux Air Guauge" which shows the presure in the aux tank which does control the air bags but this very well may be fed from the main air system (not sure how to reference the main air system)

2) If I don't have an aux. air, then can't I just level the coach and turn the key off ? Why the process of dropping it and then leveling it yet again ?

3) Do you take the measurement of the air bag from the wheeel well or do you have to crawl under the coach ? From your description of getting under the coach it sounds like you at least need to get underneath to make any adjustment. I don't know how to adjust the air bags for the correct ride height but if it's involved I suppose I should check the height first. Measuring from the bottom of a bay door sounds a lot easier than rooting inside for the air bag measurement. Is there any reason why this would not be a good measurement if I'm on a level laid pad in an RV park ?

Thanks guys.

[dalej]

Jeff you need to drop the air and let it get back to ride height on its own. Measure the bag plates, write them down and then repeat. You will see what is happening when you do this. Your bus should come back within a quarter of an inch each time but the average should be 11 and 1/2.

Jon, I measure mine on the inside of the plates. bottom of the top and top of the bottom.

[Jon Wehrenberg]

Dale,

Thats what I said, but maybe not as well.

Jeff, your comment about leveling the coach sounds like you think you will not be in the "road" or driving position. The coach cannot be in level low when taking this measurement.

As Dale points out the coach needs to "find" its height on its own. If you don't have an auxiliary air compressor or one of sufficient output, just run the bus engine and let the coach adjust itself to its normal ride height.

Measuring the height by using the air bags is a pain and if you can actually do it without the bus being over a pit, more power to you. You might want to find a truck stop with an empty pit you can borrow for five minutes.

Once you have all the air bag dimensions, then measure something that is the equivalent, such as the height from the wheel fender to the center of the hub cap or the distance from the bottom of a bay door up to the center of the hub cap. Record those dimensions and compare them to the air bag measurements, and then if necessary adjust the ride height valve arm to make the dimensions as they should be.

Because the ride height valves have some freeplay the best you can hope for is that most of the time you get the height at the specified value. I would urge that you strive to be at the specified height because the handling of the bus is affected.

[dalej]

Sorry Jon, I just read it to fast. I have to hurry when I read and post since the boss (Jan) is always watching me. She is always cracking the whip!:o

[Jon Wehrenberg]

Sounds kinky.

[Just Plain Jeff]

Get real:

http://www.worldslaves.citymax.com/i/Ball-n-chain-guy_Rubberball.jpg

[Jerry Winchester]

No Jeff, I think he likes the whip.

http://www.randomimage.us/files/4210f75ff381f.jpg

[garyde]

I have read this several times in different threads. Can you guys elaborate on where specifically to place Blocking once the Coach is Aired up full Height. Its not under the axles, and I don't want to damage the under carriage so an exact location for front and back would be appreciated.
My Coach will raise up an additional 4 to 5 inches above ride height so I am believing I can block at that height but I do not know if that Height will hold once the engine is turned off. Is it OK to block anyway? Gary

[garyde]

Hi Jeff. On my Aux. Compressor, I can hear it running when the engine is off and there is a circuit breaker specific and labeled aux. compressor. It takes a while to fill up the air bags because it has to fill the tanks first I believe. Gary

[Jon Wehrenberg]

When it is necessary to support the coach, such as when working under it, there are specific body support points and they should be shown in the coach manual.

On our vintage coach they are just behind the tag axle, and just in front of the steer axle, or just behind it.

When adjusting the ride height however you do not want to support the body, but limit how far it can fall so you can adjust it up or down.

[Jon Wehrenberg]

In a perfect world our coach auxiliary air compressors would only run when we operated something that CONSUMES air. For example if we operate the floor slide, a pocket door, or the bed lift.

But we don't live in a perfect world and we drive Prevost conversions that leak slightly (or a lot). Our bus air system automatically fills all tanks when the engine is running. When we shut down we need a source of air to operate things so the converter supplies a compressor to keep the auxiliary air system pressurized. That system can also be used on some coaches to level the coach if it leans, to supply air to the generator air bags, or to tighten the engine belts. It will not charge the braking system tanks.

If the coach is sound the compressor will rarely come on, but if it has abundant leaks it will be kicking on and off constantly. All owners should know their coaches because there are some that will dump the air in the air bags if the aux. system falls below a certain value, like 30 PSI.

[truk4u]

Good post on the aux system Jon, I'll add a couple of comments to help those who are not familiar with the system..

My Marathon has no aux compressor. Since I don't have pocket doors, air toilet or anything needing air when shut down, it's not necessary. The generator air bags are manual fill (gasp from the Liberty owners). If my aux tank leaks down the only effect is a loosening of the fan/A/C belts.

When shut down, this loss of air from the aux also has no effect on the level low. With the key off, the level low has the air bags locked up whether it's in drive or any of the manual three settings. If a bag leaks down, it has nothing to do with the aux tank, there's a leak somewhere. I'm lucky at this point, as I don't have any bag issues (yet). Now, if I turn the key on and the level low is in the drive position and the bus is not level, it wants air from the aux tank. For me, the only way to get air to the aux (remember, no aux compressor) is to start the engine or add air manually through the valve in the steering compartment. If the level low is in one of the three manual positions when I turn the key on, nothing happens unless you push one of the buttons to either exhaust air or add air and once again, I can only do that if there is air in the aux tank.

For those of you with aux compressor's, my understanding is the aux compressor keeps the aux tank charged so you can operate your air accessories such as pocket doors, etc. If you have the standard Prevost level low like my vintage and want to manually adjust your bags or go to the level drive position without the engine running, it will probably be real difficult for the aux compressor to generate enough air volume to inflate the bags. Others (some Liberty owners) also have a second leveling system independent from the level low that is suppose to keep the bus in a level position via the aux compressor. I'll bet the aux compressor is running very frenquently.

Sorry this got so long, go ahead and shoot holes in it, this is a learning experience!:rolleyes:

Lew and Harry, are you still with us?:D

[Jon Wehrenberg]

Just to emphasize a point and clarify something for the new owners. Each converter has his own way of dealing with aux. air and leveling. On our Liberty if the compressor runs a lot I have a leak. This may or may not be the case (it was on my first coach), unlike Tom's if my aux air drops below a certain value my air bags may dump air and the coach will no longer be level.

The point is you need to learn and understand your coach. Look for articles on this site and the prevost-stuff site. Ask questions, but be specific as to the year and converter.

[garyde]

Thank you Jon for the pictures. I will check it out. Is that Jack of yours a 10 ton Jack or a 20 ton? Gary

[Jeff Bayley]

Great information on this subject.

Does anyone know what the measurement should be from the ground to the bottom of the bay doors or something similar so I can check my ride height w/o taking the measurement from the air bag ? Dale gave me the correct measurement but I don't got's a pit.

[dalej]

Jeff if your coach is running a little lower then you think it should, you really should measure the bags. I know you can get close by other measurements but if you need to adjust the control rods you will have to get under the coach.

On our coach when the bus find its ride height, the rubber fender skirt is just above the drive tires 1/2 inch or so, didn't measure it. and the steer tire is just above the skirt, looking with a level eye, (might be the hard part for some).:D We have 315's on the steer and tag and 12R's on the drives.

Mine is on blocks or I would measure like you want.