Bus un-levels over time

[Jasper Sanfilippo]

Hello fellow Poggers,

I hope everyone is having a fun and safe summer.

Does anyone know why our (2003 XLII) get itself out of level? It takes about three days or so, but the passenger side slowly rise while the driver side remains level. it seems as if the passenger side is not releasing air.

Thanks for any input.

[Jon Wehrenberg]

Jasper,

Welcome to the asylum. We are going to answer your questions, but we will never promise you will get correct answers. That would be asking to much for your $10 worth of dues.

You are the first who has developed a case of the leans in which the bus rises. You say the driver's side stays level which I presume means it does not go up or down, but the passenger side rises. What will help is if you add a signature line with the name of your converter to start.

What you are describing is totally at odds with how the leveling system functions, and requires several simultaneous failures to be occuring. I don't have answers as much as I have comments. In order to raise any part of the bus, LH, RH or front the leveling system must be energized by having the key on, and the leveling control in the manual position. Even at that point nothing is going to happen until the command to raise the specific corner, in this case the RH rear which brings into play a pair of solenoid valves and two Norgren valves. Hector will correct me if I am mis-speaking.

So my initial reaction to your question is to ask you a question and that is if the RH rear is actually rising, or is the LH rear lowering. I would urge you level the coach and take accurate dimensions at four points relative to the height above the ground. When you detect the coach is out of level, retake the dimensions to determine what is actually happening.

Remember one important thing. On most if not all coaches of your vintage, regardless of who converted it, if it was a pure Prevost system unmodified, or if it was modified with the converter's own leveling or another type such as an HWH modification nothing will happen as long as the key is off to cause a leak free system to make the coach go out of level. For a coach to sink at one point or another is not uncommon, espcially as the coach ages and air bags and valves develop leaks. But to rise at one corner is most unusual and if in fact that is what is happening it suggests there are multiple issues at play, including an aux air system that never loses pressure, valves that leak to admit air into the air bags (multiple valves), and enough aux system pressure to raise the rear of the coach.

[Mark3101]

You are talking about the Prevost level low or the converters equivalent and not the standard driving ride height system, right?? Have you parked and then leveled the bus and shut it down? Also, have you started the engine during the time you are parked to build air or for some other reason?

Just want to make sure we are all talking about the same thing here...

[Jasper Sanfilippo]

Thats funny, my wife gives me all sorts of answers for free...and wouldn't you know-she is always right.

Thanks for your help. This bus was converted by Millennium. It has both the standard Prevost leveler and a HWH system.
I will get the measurements tomorrow and then track as it makes it lean. I also noticed that my aux air tank drops to 0 by day 3. The other two hold well over 100 pounds. When I leave the compressor on the lean still occurs, but the tank hass pressure.

My gut tells me I have a small leak (3 days) in a valve that allows air into the bag.

[Jon Wehrenberg]

Jasper,

Your bus is not going up, it is going down and air is escaping. I'm getting ready to drive so I can't be more specific now.

[Loc]

Jasper,

I had the same issue with my 92 Angola. Everyone said that it could not happen and that I was crazy. That was until the shop had the bus on the lift and one side raised up causing the bus to lean into the lift and put a dent in the side. After that they finally believed me. If I remember correctly they changed a couple of Norgren valves and that fixed it. The shop was never fully sure what caused the problem.

Loc

[Jon Wehrenberg]

Jasper,

Don't believe Loc. He has a drinking problem.

Well, OK, he is correct with respect to his coach, but when you said the aux pressure is zero that rules out the possibility the bus is raising.

First, If nobody has invted you or made you aware, come to Austin for our rally on Oct. 3rd. details are on this site and the Prevost-Stuff site. One of the seminars is an excellent one relating to the air syustems and the suspension. All the mystery will disappear after you attend that session.

Since you coach is lowering due to loss of air (the fact the aux system has no air is NOT why your bus is leanin. Two separate unrelated issues. You have a leak somewhere in the area of the three air bags in the rear on that side, or the associated valves, or fittings, or the accumulator tanks. The leakage isolation could be made more difficult because your coach is approaching the age at which experience has shown components in the suspension system are going to start leaking. Cold weather will make the leaks show up much quicker.

Come to the rally. We have sheep.

[Jasper Sanfilippo]

I thought it was a prerequisite to have a drinking problem when owning such complicated motor coaches.

I will buy everyone a drink if this bus isn't somehow rising on the passenger side. So, let me explain a little more. First the bus is parked on a pad thats pitched from passenger side to drivers. (I do get the excessive slope indicator, every now and again)

I will get it level and then over a couple days passenger side rises, while the drivers side sinks. (aux tank will go empty without the compressor on...if I leave the comp on the same result occurs, but the tank has air). From here I've tested differet outcomes. Scenario 1, dump the bus, leave the compressor off (aux is already empty) and the bus stays in the same place from the dump position. Scenario 2 dump the bus, do not try leveling, leave the compressor charged and the bus will develop the lean. Scenario 3 dump the bus, relevel the bus, turn the air off and the bus leans, while emptying the aux tank.

There is no question there is a leak on the drivers side airbags, but I do believe i have a leaking valve that is somehow
Back filling the passenger bags and making them rise.

[truk4u]

Jasper,

The only way you are able to get inflation to your airbags with the standard Prevost Level Low is with the key on and it's a manual process. I understand you have HWH and auto leveling while parked and to accomplish this, you must have aux air. If the HWH is hot all the time and programmed to check the level every 30 minutes or so, you should hear the aux compressor running when it does it's check if it's putting air into the side you say is rising. This of course depends on the amount of air in your aux tank.

I have had this system before and the process you describe would lead me to the HWH sensing adjustment located somewhere in a bay, usually on the ceiling of a bay. This is where the leveling system get's it's information and may need adjusting. You would first have to manually level and then re-adjust the sensing device.

If this doesn't correct the problem, then a call to HWH (have fun) would be in order. A call to Millennium may also help, but you won't get much help from Prevost since the converter has overlaid the HWH on the level low.

[Jon Wehrenberg]

I will stick with my opinion that unless the air in the aux system is maintained at sufficient pressure to raise a coach at the left or right rear there is no way one side is rising. Going further, even if the coach could rise because there was a constant supply of auxiliary system air pressure there would have to be a leak in at least two Norgren valves such that auxiliary air pressure is leaking into the air bags and not to atmosphere. That path for the high pressure aux. air would have to be through a three port Norgen in the front and a five port Norgren in the rear.

One of these days it would be an interesting exercise to measure the air pressure required to raise a coach of known axle weights at each of the three positions. My reason for wanting data such as this is to make system limitations known. For example, if a coach has a pressure requirement of 120 PSI to raise the front up to or above ride height, and 85 PSI to raise either rear side to or above ride height, then it follows the aux air compressor must maintain the aux system pressure to at least those values or automatic leveling features, with the engine off are not going to function.

[gmcbuffalo]

Jasper when you say the passenger side raises are you talking about the front end or rear end or both?

[Steve Bennett]

We had the right rear of our coach raise up about 2" at the Kerville rally last year. We cycled the Prevost level low solenoids/valves, and we have never had the problem again? If the rear is un-level it will cause the front to be unlevel as well, unless the front suspension is sitting on the bump stops which would tend to help hold it level. Our coach has the standard Prevost Level Low, and our aux system was at about 100PSI in the morning. We did not have our aux compressor on. My guess was that the rt rear solenoid valve did not seat completely, and was letting the air from our aux system pressurize the rt rear bags.

[Jasper Sanfilippo]

OK folks, here is some realtime information; and by the way thank you for taking the time to help. That is what makes this group special....and some sheep???

When the bus is leveled using HWH (Level-driverside) 6.75'' from ground (Level -passenger) 10'' from ground
When the bus isn't level using HWH (Un-level -driverside) 6.5'' from ground (Un-level-passenger) 13'' from ground.

So, can a 1\4 to 1\2 inch fall on the drivers side translate to a 3'' lift on the passenger?

the rears were equal at 17'' on both slides. "may pad has some dimensional run outs"

[Jon Wehrenberg]

Yes it can rise as has been pointed out, but to do so involves either some perfect combination of valve leaks plus maintaining a good auxiliary system pressure (which you previously stated was down to zero) or the HWH is trying to reach a level condition that is different from the original one.

The bus cannot go up unless the air pressure to lift it is avalable. That pressure can only come from the aux air system (never from the primary or secondary brake circuits).

Have you tried to measure what happens if the bus is leveled and then the HWH is not attempting to level it? I assume that auto-level feature can be turned off?

[truk4u]

Did this just get ignored?

I have had this system before and the process you describe would lead me to the HWH sensing adjustment located somewhere in a bay, usually on the ceiling of a bay. This is where the leveling system get's it's information and may need adjusting. You would first have to manually level and then re-adjust the sensing device.

[GDeen]

I wonder if there is some sort of sensor with the HWH system that may be at fault - anyone have any ideas?










:cool:

[Jasper Sanfilippo]

I do want to clarify one thing; the air pressure in the aux tank goes to zero only when I kill the breaker for the compressor. (clearly a sign of a leak). When I leave the compressor on the bus still get out of whack, the aux tank remains pressurized, but the compressor cycles. (cycles about every 2 hours or so)

[Jon Wehrenberg]

Jasper,

There is one thing that owners have a hard time embracing. The bus, if leak free in the suspension system, will sit level regardless of how much pressure is in the auxiliary air system. If the aux system is zero, the bus will not necessarily lean or drop.

If your bus is rising because you have pressure in the aux system the diagnosis has to start with the HWH system to make sure it is set to "level", then the solenoid valves to make sure they are not holding pressure against the Norgren 3 and 5 port valves, and then the 3 and five port valves to make sure they are not leaking air pressure into the rear air bags.

For your problem to be the perfect combination of valve leakage seems extreme. I would give special attention to the HWH as Truk indicated.

[Loc]

When you level your coach are you using the HWH exclusively or both the HWH and Level Low? When I level my XLII I use both the HWH and Prevost Level Low. I first put the Level Low in one of the non-drive positions (it doesn't matter which one), then I engage the HWH and level the coach. Once level, I turn off the HWH and the engine (it is much easier to level the coach with the engine running than relying on the aux air compressor). With the HWH off and the Level Low set in the non drive position I have yet to experience any unleveling issues with the bus using this procedure. I did find a couple of times that if I did not switch the Level Low to the non-drive position the bus would change level.

[Jon Wehrenberg]

Loc's post reveals something that owners have to determine. How did your converter set up your suspension system and the HWH?

Does it function with the key off? Does it operate all the time? Does the level low have to be in a non driving position in order to funtion as an automatic leveler? Can the automatic leveling be turned off?

[Jasper Sanfilippo]

Thanks for the advice. I will try doing that tomorrow and post the results.

[Jasper Sanfilippo]

Ok so here is the latest;

Went to the NASCAR race this past weekend a parked on a relatively flat spot. The bus had no problem leveling and in fact, stayed level the whole time (3 days). When I park at home my spot is out of the leveling range and I get the excessive grade light. Could it be the HWH system is getting out of whack, or losing it's position because of the excessive grade?

[truk4u]

Once again, the level sensor!