The Leans....Episode II

I'll stick my neck out here and make a bold statement without benefit of facts or specific knowledge.

I would like to do the same seminar again, but except for briefly showing how the system on our suspension works, I am going to try to get very specific about which components to really zero in on when trying to correct the leans.

I am still learning this so I have a few months to satisfy myself that there are some specific components that are solely responsible for keeping our airbags pressurized (actually they are responsible for not allowing the pressurized air to escape). The only concern I have is that I need to make sure my Liberty is not so different from others that I will mislead anybody.

Here is why I think this complex topic can be reduced to simple terms. When we level the coach and shut it down, I think a single Norgren at the front, left rear, and right rear closes off all air flow from the air spring (air bag). It may be more complex than that since I know there is a little complexity in the rear due to the ability to dump air in the tag, but I will sort that out. The reason I think we can verify that a single Norgren per location does the job of sealing off air to the air bags is if that were not the case in all instances then the ride height valves would be working to supply or exhaust air to the air bags if the front or rear corners were not at the road height.

The goal will be to get us past the mystery of the leans.

If I think I have it I will try to be in Sevierville and Pahrump. Stand by for updates.

Ok Jon, as a newby actively in the market for a Prevost bus, could you give me the 3 minute rundown on "the leans?" The term itself provides a good visual, but an explanation would be helpful.

Thanks!

GDeen,

The "leans" used in the context of our coaches is when a coach that has been leveled at a campsite, or merely turned off in our garage starts to lean to the left, to the right, or settles down in the front.

Our air bag suspension (you can see the air springs or air bags as we call them on the rear of semi trailers or trucks) is supposed to hold our buses up where they were when we shut off the motor. But over time, and especially in colder weather the system develops leaks which allows the air bags to deflate. According to Prevost, if the bus remains as parked for at least three days the system is OK. I think most of us are willing to accept that as a reasonable amount of time before we have to relevel the coach.

But if left without repairs or maintenance the coach could start leaning in a day or even hours in some extreme cases.

Without getting too windy here, the bus suspension system is complex with hundreds of fittings, at least 19 valves, and eight air springs. Leaks can occur at any of those components and what we as owners seek is a fairly easy and logical way to pinpoint the problem to eliminate the leans.

Jon,

For additional "limited" experience. On the '97 Liberty I found that the 5 port Norgren's controlled adding air to the bags and the 3 port ones we're responsible for dumping air. This held true both in the steering bay and back in drive wheels bay.

Mike

Now that I stuck my neck out I'm going to start assigning what specific task each of the valves controls, and most importantly determining which specific valve is the one that shuts off all outflow from the air bags.

In addition to the plywood mockup I may create a huge poster with the locations and assignments shown in the proper relation to one another.

I have to believe with proper study we can create a flow diagram for systems problem analysis and repair that eliminates the guesswork about which valve is responsible for which function.

Since I am going to re-do my entire leveling system valve train before the April rally I think I can do this.

Ok, so the leans are due to leakoff from the bags after the coach has been leveled and turned off. Is that something one should test in a used coach when evaluating it for purchase?

Thanks for the explanation Jon.

Gordon

If I were going looking at a bus there is a ritual I would preform on every one I would look at in terms of your question about air.

I would start the bus let it run till it builds air up to 120lbs. Do this with the window open so you can here the air dryer sneeze, it will do that right at the point where the air compressor tops out and stops. At that point shut off the bus and note the time then continue going over other things and go back to the gauges after 1/2 hour and note the pressure drop, if any. There should be little or no loss in this short period. I think just by preforming this you will be sending a pretty good message to the seller in terms of if there is potential
issues and weather or not he thinks you'll find them.

Then chock the tires so it wont roll, release the parking brake and do the same thing again, start it up run it till the dryer sneezes around 120lbs shut it off and again check for air loss with the parking break released and again after 1/2 hour. If the result is different from the first test IE now a loss where there was none or a greater loss, that is an indication of air leaking from the emergency side.

Finally with the bus aired up and turned off, breaks released, step on the brake pedal and hold it steady and watch the gauges again for any drop, a leak found here would be a service air leak.

That would be an initial inspection for me and if those tests turned out O/K and I were really interested in possibly buying it I would then do an overnight pressure loss test and I think I would not accept any bus from anyone that did not have at least 90 lbs of air the next day unless of course that issue was reflected in the selling price.

Joe has just described what we all should be doing as a pre trip inspection, and I'll be the first to admit I do not do that as often as I should.

As to the question about inspecting a bus for the leans......it gets a little complicated. For example, the inspection of a bus will require the running of the engine not only for what Joe recommends, but for other reasons, such as to get things up to temperature to check certain fluid levels, for a test drive, etc. You will not be able to learn the bus has some air losses unless you let it sit overnight untouched.

A bus usually has a serious suspension system air leak if it is detectible in a few hours, and even if you were to be faced with the replacement of every single component in the suspension system, such as the valves (every last one of them) the air bags, and the solenoid valves you would spend about $2200 to $2500 and about 15 or 20 hours of labor. That is not pocket change, but if that is the only expense associated with buying a coach it is relatively small. There are other far more serious items to examine closely, like the engine and transmission.

In the inspection of a bus by a new buyer I can say without fear of contradiction there is so much to look at and evaluate that few do it the way we seasoned owners suggest. That's for another thread, but the only real way to really know if you have issues such as the leans, problems with the inverters or chargers, the generator and its starting protocol, and other systems is to live with the coach for three days or so before exchanging the final check for the title.

I want to add one comment to any discussion about the leans and the health of the suspension system and the auxiliary air system which feeds not only the suspension, but every other air operated device on the coach except the brakes.

You can lose 100% of the air in the auxiliary air system, and it is possible the bus will not have moved as much as a fraction of an inch at any point with regard to its height. Conversely, you can lose 100% of the air pressure in the front, left or right air bags, and retain 100% of the auxiliary air system pressure (assuming no other components are leaking).

One more point Gordon, and this is critical to understand because it underlines why Joe feels the air systems that read on the gauges on the dash should not show a pressure drop of consequence overnight. When the bus is stopped with the parking brake engaged, not a bit of air or air pressure is applied to any braking system component. Air is only used in the braking system on diedicated lines to release and hold released the parking brakes, and to apply the service brakes.

Joe - Keep in mind if the bus doesn't have an aux air gauge, all your doing is verifying the brake system is good and the accessories and air bags could have leaks. The aux air gauge tells the story, whether dash mounted or in the steering bay.

Jon, one point I brought up during your seminar with Bill that didn't go to far was how you can help determine aux air leaks by the gauge. My CC has the aux gauge in the dash and while driving, if the road is straight and level, there should be very little loss of pressure. Once the suspension starts using air due to road conditions, it's real easy to watch the gauge and understand whats going on. My governor is set at 125 on the high side and 100 on the low side. If your on a good road and your aux gauge is depleting an excessive amount of air causing the compressor to cycle often, you have leaks somewhere. There is always a little air being used, but you can tell if it's excessive. Mine goes about 15 minutes on good roads and will cycle every 5 minutes if the suspension is working hard.

In my opinion, thats one of the down sides to the new quick response leveling valves, they cause the compressor to cycle every few minutes. I experienced this on a plastic CC pusher, where the compressor cycled every 1 1/2 minutes during curvy road conditions. I added a second aux tank just to get more time on the compressor cycles. Compressors wear out, that's a fact.

So, if you don't have an aux gauge, at least install one in the steering bay to help you determine if you have leaks. Or, just check the belts in the rear, if they're loose, you gotta leak.

Jon - I keep digging, learning and reviewing the Pneumatic systems to better understand the aux system and would be glad to help you. I'll even run up to TN for a planning session if you like, providing the King buys dinner for us.

Jon,

I would very much like to be in attendance at your next "air" seminar. So far, everything looks pretty good on my bus, but you can never be too educated as to the why and how things work.

Thanks for all your efforts in undertaking this project!!

Zen and the Art of Detecting Leans?

(Oh no, here he goes again)

Having lived with this problem for many years in various coaches, the discussions with techs, rallies, here on this forum, etc., it's clear that the air system of the coach is very complicated and I am not sure that we have a complete fix on how every coach's air system operates in a precise way.

There are year-to-year differences between the delay and non-delayed systems, perhaps even some VIN number coaches, converter tap-offs for sliding steps, toilets, doors, dump valves, what have you.

And, we also have the differences between coaches moving and sitting. Then there are differences between those sitting while running and those with the ignition switch off.

Adding to all of this is that from what I can figure out, the Prevost system is basically a closed system; that is, when air is released to change the position of the coach relative to the ground, it does not escape from the system, it goes somewhere else.

To further complicate this issue, the tag on coaches I have seen, uses a brake chamber to help regulate the tag. Tag action on say, a 92 40-footer is quite different than that of say, a 98 XLV. The 92 will lift that sucker right off the ground and the XLV will ease off the tag somewhat, shifting the weight rather than a lift and drop movement.

Most of us have probably seen an old banger of a seated coach bus going down the road at about the 2 o'clock position, wondering why someone didn't maintain the air system.

Not to create a silly argument here, but in pursuit of The Grail, it might be good to stick with a particular coach in a particular mode so that we can come together and understand how that one might work, let's say in a parked mode with the engine off. Since some of the leaks in the components of an air system cannot be detected by soap and bubbles, maybe that would be the first thing to take a look at and understand.

In a dynamic system, which is what the Prevost air system is, with multiple variables changing in parallel, defining each part of the puzzle first is one way of figuring out how to describe subsequent events and how they relate to that one snapshot that we can understand.

So that's 2 cents worth and you can keep the change if you want. I'll stop writing right now.

Tom,

When in transit the aux air for the suspension is going through the ride height valves into (or out of) the air bags.

I have not watched gauges on a coach equipped with instant reacting ride height valves, but I have extensively on the delay reaction valve. On what we consider smooth level roads with the delay valves there is very little cycling of the compressor due to the filling and exhausing of air in the bags. As we get side winds, change lanes (the crown tips us), or have undualtions you would begin to see air consumption.

I suspect but do not know for sure that the instant reacting ride height valves dump air and refill constantly, even when we are not aware of changes in the road, the winds or the crown.

I was doing some homework tonight and I have to get under the bus and compare my actual system against the pneumatic diagrams Prevost has on line. I thnk the ones I am looking at on line are for seated coaches without level low. If you want to play maybe we can set up a day to work in Casa del Grease Pit.

JPJ,

This will require some investigation, but I suspect while the systems may in fact vary from converter to converter and from model and year to model and year, I think there are going to be some generalities that we might be able to make that will help almost all of the POG attendees. (Obviously I have a Liberty to use as my learning tool, but I know guys. And these guys can look at their CC, and Marathon, and Royale, etc. and we can all compare notes.)

I say that generalization because when some converters create their own variations, they appear to not alter the valving, as much as they create an additional electric system that piggy backs on top of the Prevost provided leveling controls. When the coach is in the "automatic" or self leveling mode that switch position just takes the manual controls from the Prevost circuitry and the automatic circuitry becomes the control of the valves via the solenoids.

The more we dig into this, the better our understanding of the variations will be.

this would be an ideal place and time to announce that Mr. Paul Horner was giving tours of the compartment under the drivers area. He is so very proud of his newly installed pressure guage.

I told him it should have been tilted for an easier read. This was said after I stood in line for a while to see his installation. What a smile he had on his face. I told him that Jon would be very proud of him. No light though, he won't check it at night no matter how much you want him to.

Thanks Joe and Jon for the detailed answers to my questions...I have a lot to learn!

I've got it.

I have been crawling around under the bus, looking at schematics, studying parts lists and diagrams and generally trying to get a handle on this whole topic we call the leans.

I'm done. At the spring rally we can review the miniature single air spring suspension system, but instead of looking at the entire topic as a big puzzle we can break it down into specific valves and their individual functions so it will make pin pointing problems less intimidating.

The deeper I get into this (starting with building a mockup) the simpler to uderstand it becomes. I will not mislead anybody into thinking if the coach leans to the left it is a simple matter of replacing the single valve responsible for keeping the left side air bags inflated. There could be any number of reasons why the coach is leaning, but at least you will be able to understand exactly which components could affect the left side, and how to verify they are the culprits or they are not the problem.

I have written a 14 page article. I am going to let some folks review it this weekend, and if they understand what I am outlining I will see if we can get Jim to post it.

When we get done with this thing called Prevost we should be able to understand the whole thing.

Jon,
I can't wait, I used the bus this weekend and when I went to lower the front, nothing! It would air up or down left and right back and up the front but not down.
I just got home and did a little more playing with the Prevost rotary switch and I found that if I go down with one of the rears and then try the front down, it works. If I try to go down in the front after going up on any of the 3 positions, nothing.
I will play with it a little more in the morning, any ideas?
Kevin
I will post a story about my engine driven air compressor tomorrow.

Kevin,

I can give you some clues, but remember...I am doing my looking on a Liberty, reading diagrams from an unaltered Prevost system, and looking at Prevost pneumatic diagrams on line that do not match anything else.

But if you are still interested I will tell you where to look.

The second solenoid down (in the five valve assembly in the steer compartment) controls the front air control valve. The five port and the three port valves in the steer compartment control the blockage of flow into and out of the front air bags (the five port valve) and the adjustment of the height of the front air bags (the three port valve below it).

I would make certain the solenoid valve is opening when you command it to via the switch on your panel. If it is, then make sure the five port valve is functioning, since even if the three port valve is not funtioning, the five port should shift the spool and allow the ride height valve to come into play.

I think you have a generic system, and I think the above is valid.

My guess is the bus has not had the system exercised and once you get things moving the problem will go away.

Kevin, I'm not sure it is necessary to check this, but I want to make sure this is understood.

The third solenoid valve down drives the opposite side of the five port valve and it is that action that puts the ride height valves into play.

Jon,
Thanks, Marathon does not add anything to the Prevost level system. I think that it should be the same as yours. I will look at things in the morning, I will also exercise it as much as possible to see if that will free things up. Thanks for the info and I will keep you informed, this will be my first look at this stuff, I kinda am looking forward to feeling my way around those valves----kinda sick I think!
Kevin

Marathon does in fact add or modify the Prevost system, but not necessarily on all of their coaches. That is what makes specific information impossible. Liberty does modify the system on all of their coaches (I think), but I know for sure their modifications have varied because my two Libertys had differences.

My guess is that based on the age of you coach if you haven't started experiencing problems you are about to. Not a criticism of the coach, but just a fact that mechanical things need maintenance from time to time.

Jon,
Yes, I agree that the time is now for those problems to start showing up. As soon as the sun shines thru the wind, I will take a look at things.
A little info on my engine driven air compressor, when I did my first service after buying this bus in June of 05, I noticed some oil around the frame at the air dryer spitter. I changed the filter and just kept an eye on things for the past 2 years.
Last Wensday I picked up the bus from storage and I noticed that the air gauges where only at 100 PSI, I fanned the brake pedal down and no air pressure building. I called my local truck parts guy and he recommended changing the regulator on the outside, the most common part to fail.
I went and picked 1 up, changed it in the RV storage drive and it worked.
When I got to our shop and parked it I noticed low air pressure again, this time it would not build air. OK, there is one more thing you can change before the compressor, so off to the parts store, back to the shop and changed 2 small piston type valves in the top of the head, no luck!
150,000 miles and I had to change the compressor, the only good news was the bus was sitting in our shop and about 6 hours and $1000.00 later and I now have a reman pump and when I get a little time I will clean all the oil under the frame and start monitoring oil out of the air dryer from the new compressor.
Kevin

If it was passing a lot of oil, it is likely the media in the dryer is coated with oil. When that happens the oil passes through the dryer via the spitter. You may have to change the dryer cartridge, which creates something for you to think about.

If the media is oil soaked, and you do not change it, it will not absorb moisture, but with a clean frame you may be able to determine if oil is passing through the compressor. Or if you do change it, any oil (and moisture) passing through the compressor will be absorbed by the dryer so you will not know if the compressor is OK.

I'd go with a new cartridge and a clean frame and then keep an eye on it.

I'm probably now in the range of age and miles where I need to be aware of losing a compressor and an alternator. And an OTR compressor, brake linings on the drive, power steering pump, etc. Geeez these things are a PITA.

Jon - Great job and I know everyone appreciates your time and efforts.

Kevin - Your experience is why I made the post about the aux air system and the importance of a panel mounted aux gauge to monitor what's going on, compressors really DO wear out. I had the pleasure of a compressor change out in my Foretravel while traveling, ouch! I carry a spare governor, but it never seems to be the cheap part. Good job on saving some race bucks..:p

Tom,

Maybe we should see about writing a compressor replacement article and a guide to trouble shooting it?

I'm rebuilding my OTR compressor this winter and will document it, but except for Liberty folks that is an article with no readers, and most Liberty folks won't get into that level of repairs, but an air compressor article will have broad interest.

Lets talk this weekend.

Quote:

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Originally Posted by Jon Wehrenberg

I've got it.
I have written a 14 page article. I am going to let some folks review it this weekend, and if they understand what I am outlining I will see if we can get Jim to post it.

---

Jon are you writing this in a Word Doc. so that it can be posted and printed by others, easily?

Thanks for all of your hard work, I know everyone appreciates it.

I too will appreciate it, some day? :(

Gary S.

Well, as thing go, it is always hard to trouble shot problems when they work. I tested the front air down every way I could, many times and it worked perfect.
I did change the filter last Thursday at the same time I changed the compressor, didn't want to wait and it was 2 years old anyway. This morning I spent some time cleaning the frame and I will watch how oily it gets---I hope no oil at all.

I did find that when I pulled the compressor that there are 2 engine sensors behind it. One is triggered off the crank and the other is triggered of the gear up a little, now was the time so when we went to Detroit for the compressor, we got both the senors and I hope I paid for a little insurance. There is also a water hose that goes from the block to the head of the compressor and of course it is on the back side so that was replaced also.

Time will tell on the front level valves, I am sure they will fail when I am camping and need to use them, that is always the case.

Jon, thanks for the info, I will keep it for future use.

Kevin

Gary, I sent it to Jim Skiff to post on the front of the POG site. My computer has a Microsoft word processing program. That is what it is in. Once he posts it everybody should be able to print it out.

Kevin, My guess is you loosened the system of valves up so they work now. How about doing a compressor seminar or writing an article. I know it is coming with my coach and I can think of some others of the same vintage.

I would be more than willing to do a seminar, my writing skills suck! I am looking at 08 and it looks good for Sevierville. I will have my bus there unless a Bunk model has my name on it somewhere.
Kevin
Skiff, let me know if this works for you.

Kevin, if you do a compressor seminar I'm signing up.