The Leans....Episode II

[Jon Wehrenberg]

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.

[GDeen]

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!

[Jon Wehrenberg]

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.

[MangoMike]

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

[Jon Wehrenberg]

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.

[GDeen]

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.

[Joe Cannarozzi]

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.

[Jon Wehrenberg]

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.

[Jon Wehrenberg]

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.

[truk4u]

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.