The Leans

According to Prevost Car Company, any given coach should be expected to lose about 5 lbs of pressure/hour. This means that overnight any coach should experience some auxiliary air loss. A cool night will result in even more apparent air loss as the air in the system compresses. So before pursuing valve problems or leaks, a little information is a lot of power.

I will strongly disagree with the Prevost posture on this one.

Admittedly the systems are very complex and contain many potential leak sources, and adding to that possibility it can be expected that as Jeff's post points out cool ambient temperatures will tend to amplify any leakage. But, there is not a single valve or fitting on our coaches that are designed to permit even a small amount of leakage. All are expected to be leak free under pressure.

I think the Prevost opinion is intended to stave off screaming and shouting from new conversion owners who have the leans. If you want to give their comment the sniff test apply the same statement to your tires. They are also pressurized with air and have a valve. You wouldn't accept a leakage 1/10th of what Prevost considers acceptable in the bus air system. If a $1.00 tire valve is expected to hold air pressure with no loss, why is it not unreasonable to expect a Norgren valve costing hundreds of times more to also hold air pressure? Going further, according to the Prevost 5 PSI standard (per hour) an owner can expect that within 14 or 15 hours of parking their coach it will require re-leveling. In fact, in some systems if the aux air drops below about 30 PSI air might be dumped from the air bags. If that posture is the official Prevost stance on air system leaks I submit they are asking for a highly agitated customer base.

The worst part of that posture is it puts the customer squarely in the middle of the converter and Prevost, both of whom have some responsibility for the aux air system.

The effort to find all minor air leaks is often considerable, but with patience and sometimes the right tools it can be done.

You will notice that I never said that Prevost Car Company's assertion was actually true. I think it is a CYA for the company in general; including seated coaches, entertainer coaches as well as conversion coaches in general.

Of course, one of the larger issues with a converted coach is the level of integration into the systems that various convertors go into the aux air system. The greater the use of aux air, the greater the chance for leaks. The secret here, as in all maintenance operations, is to get ahead of any potential problem long before it becomes a problem. Chase down two leaks is more than twice as difficult as a single leak.

I am surprised that someone didn't figure out that I used italics to symbolize leans during this post.

And I thought we had some detail oriented folks out there. Hmmmm.

JPJ,

Completely missed the symbolism. Perhaps it was the importance of the message that was distracting.

For those not familiar with the air system in their coach, Prevost will bully the person into submission, because after all, they build the coach. For those who have a basic understanding the Prevost posture on air leakage will be clearly seen as absurd. Especially for seated coaches. If Prevost actually thinks they are protecting themselves from unreasonable customer expectations they are wrong and I hope they amend their air loss guidline.

Now after a day in the RV park, I seem to have the sags as well. I had to relevel the coach this morning and it seems to be riding low in the rear after having been out all day.

It may take a while to sort all this out, but I can't understand that if there is air in all the tanks, why won't the coach stay level until the air is below the pressure level required to keep it so?

Jerry,

Lets assume you never lose any pressure in your tanks. Or you lose all the air in your tanks. That is not related to the air in your leveling system which includes the valves and air bags.

When you air up your bus, and the suspension system has air so the bus sits in either the road height position or in a levelled position, theoretically you will no longer consume air and if all systems are perfect your compressor will not need to run. When the suspension switch is set at road or manual position and the other three switches are off your air suspension is isolated from the other air systems. It is "shut off".

So when your bus starts to lean it means the suspension system is leaking air to atmosphere somewhere.

Conversely, if your air suspension system is leak free, the air system for the bus can leak down to zero pressure, but your bus will maintain the set height.

JPJ made an excellent point that is often overlooked by conversion owners. They tolerate a small leak here and there, and pretty soon when the problem becomes serious enough to demand attention the problem is no single cause, but perhaps multiple minor sources of leaks. At that point you go crazy because you find a leak, fix it and think the problem is solved, only to wake up in the morning with a bus sagging again.

This is an oversimplification, but if you can think of the bus air system as two parts. One part is the primary or brake system. This system only uses air for two purposes. It uses air to release the emergency brake. If that portion of the system is leak free, when the emergency brake is off the only other consumption comes when you step on the brake. As long as your foot remains on the brake the air is not consumed, but routed to the brake chambers. Only when you lift your foot from the brake does air exhaust to the atmosphere. With your emergency brake "on" and your foot off the brakes there is no possible loss of air in the primary system unless you have some leakage in fittings or the tanks or some check valves. This air loss has nothing to do with the suspension unless there is a leakage between the primary system and the auxiliary system.

Your suspension is your auxiliary system. It is isolated and independent of the primary system when the bus is parked and shut down. The aux system contains your belt tensioners (unless you do not have OTR air on older coaches), genset air bags, floor slide, pocket doors, and your leveling system. If your bus leaks down overnight and sags at the very least I suspect your have a leak in a Norgren valve, a leak in the Prevost valve pack, or a leak in the air bag. If you have an older coach you are likely to have multiple minute leaks almost everywhere. I doubt if there is anybody in the world that can tell you where to begin looking.

I make that last depresssing remark on the basis of the fact that each conversion handles leveling in their own way, and Prevost also made some changes over time. For example, my 87 could be leveled with the key off. That meant with the bus shut down the aux and primary systems still were interconnected. My 97 requires the key on so when the bus is shut down a solenoid valve (I'm guessing) isolates the two systems.

If you want to spend a day under your coach you will be able to find some of your "leans" with soapy water and a stethoscope. But you will also have to check in your engine compartment, and the front lower compartment, and you will also have to be lucky.

Don't tell anybody with MPD about this until after they buy their coach. No need to scare them.;)

Great post Jon.. On my CC, I added a gauge for the aux tank so I could see any loss of air. As the air in the aux tank bleads off, you know you have a leak somewhere. The gauge also helped in determining if I had enough air in the aux with the engine off to raise a bag for leveling, as the 12v compressors didn't have enough volume to pump up a bag. On my Marathon, there is no 12/24v pump, so if you don't have any aux air, the only way to level is starting the engine.

I believe some of the conversions have an aux gauge and I'm going to add one. The idea of carring a 120v pancake compressor as someone else mentioned is a good thought for always having an aux air source, but you really shouldn't need it if your leak free..

I had a problem with the front air bags loosing air when I got the bus, but it hasn't happen again and the bus is dead level after sitting for a week leaving the level low in the drive position. I may have a leak somewhere when leaving the valve in a position other then drive and it maybe at the valve itself.

Now it's time to press some idler pully bearings.....;)

I have an unregulated aux air gauge and a second gauge to monitor the regulated air pressure (set at 60 PSI in my coach). I rely on the dash gauges for my primary and secondary air. Excellent point about using the aux gauges to monitor leaks.

I think Tom brings up a point sometimes overlooked and perhaps Jerry should consider this. How you level your bus and then shut it down is important. I can almost be assured of leaking air if I turn my coach "off", and then switch the level low from automatic or manual to the road position. If however I level the coach, and then switch to the road position and wait about two seconds before turning it off I can sit for about a month before I detect the start of the leans. Each converter may have their own way to do it, and maybe Prevost has their own way but the way I described above has proven successful for my coach.

What a dummy I am, found an aux pressure gauge in the steering bay and it was on "0". Pumped it up with garage air and within an hour I already lost about 20 lbs. You will see my other post on the tension air bags.:(