Tag Axle Valve?

[ajhaig]

We've been parked at a camp ground (Fort McDowell just outside of Scottsdale, AZ - nice place) for a little over a day. Tonight I was standing next to the bus when suddenly I heard a loud air sound coming from the rear of the bus. It was the same sound that I hear when I raise the tag axle. The bus didn't seem to move noticeably.

In thinking about the sound, I've noticed that when I start the bus after it's been parked for a few days the tag axle indicator light on the dashboard comes on. The light goes off as the bus airs up.

Could I have some sort of faulty valve?

Thanks again.

AJ

P.S. This guy joined us for breakfast!

[Jerry Winchester]

AJ,

Not to hijack your tag axle post (when the air gets too low the tag axle dumps), I am headed to Phoenix the day after Christmas and have been pondering about a place to park for a few days. We are going to the bowl game on New Years Eve in Tempe, but for all the gazillion parks in the Phoenix area, most seem like snow bird places and very few seem to be set up for folks to come hang out for a few days and move on.

Any suggestions would be appreciated.

[ajhaig]

Jerry,

We are in Eagle View RV Resort, Fort McDowell (I think there may be several RV parks in Fort McDowell). I would recommend this place, it's quiet, clean and relatively new. It is on an Indian reservation and connected with a casino (the casino is about a mile or so away). I think it is in Big Rigs. We did the ride to Tempe today, it's a straight shot down route 87.

The place seems pretty empty now, but they told us that they get very busy after the holidays.

There is an slim chance that we will still be here through Christmas.

AJ

[Joe Cannarozzi]

You have an air leak. Right before the pressure drops to the threshold of activating that valve the valve itself will begin to exhaust and the sound of air will get more prevalent and loud. Around 40 psi or so.

[Jon Wehrenberg]

AJ.....some coaches of an earlier vintage had a system design that required a specific auxiliary air system pressure to hold some valves closed. Typically if the pressure dropped below that required to hold the valve closed against the spring plunger pressure (somewhere around 30, but Joe may have the more accurate number) the valve would open and air in the rear would dump, usually allowing the bus to settle down.

I don't know what year Prevost redesigned the system, but I think your bus precedes that design change.

It is only a problem if the aux air system loses pressure, or if you have system air leaks, even minor ones. Prevost was aware of the glitch that showed up as the coaches began to age, and there was a change that they could make at the service centers to eliminate that design error. I may not have it completely correct because a lot of owners had the upgrade done and that was a long time ago and my memory has faded.

[Ray Davis]

My '93 did the exact same when the aux system got low enough. There is a retrofit kit from Prevost, however it's very expensive. My recollection was that it was somewhere in the $2000-$2500 region.

I chose to live with it.


Ray

[ajhaig]

It sounds like we need to get checked out for leaks and resolve the issue we have been having with our aux air compressor so we can use it.

I've heard good things about Desert West Coach in Phoenix, has anyone had any experience with them?

Thanks everyone.

AJ

[Jon Wehrenberg]

AJ....(free advice is worth every cent you pay for it) among the POG members I would suspect that one of the most expensive and least rewarding repairs to our coaches has been the air system, excluding the brakes.

The suspension control system consists of valves and airbags and hundreds of fittings. The house is likely to have more devices that require air, ranging from the driver seat to the floor slide and a bunch of other things that vary from converter to converter. If you have OTR the extent of the aux air system runs from the very nose of the bus all the way to the air bellows for belt tensioning.

It is probable that even the most skilled and knowledgable repair facility will eat money out of your wallet faster than a horse eats oats.

I spent two weeks in my garage with my current coach chasing every air leak and getting the system tight enough so the system pump runs only once a day, if that. But I started with a bus that didn't lean and didn't have very many issues. The sources of leaks are endless and insidious. You can do a whole lot yourself and should, unless money is no object. A stethoscope from Sears, a spray bottle with water and kids bubble mix, and a quiet place will be all you need to locate almost all of the ones accessible without going under the bus. That includes the steer compartment and the engine bay.

When you get that done you may have solved most of your leaking problems. But if they continue remember, when the bus is parked there is zero pressure on the brake system so that does not need to be checked other than the pre-trip inspection. That leaves the suspension system. On that, the air bags can have golf ball sized holes in them and if you are shut down, they will not drain the auxiliary system because 3 of the Norgren valves are shutting off flow to or from the air bags.

Now you are down to the pneumatic operators alone under the coach. The rest of the suspension control system leaks would have been in the steer compartment. Since your system is likely to leave pressure on the operators on the ends of the Norgren valve actuators, that is the place to check under the coach. If they are leaking it should show up around the pneumatic operator end cap. That's my bet.

The reason for this treatise is if you understand what I said above....you know exactly where to look and likely now know more than a non-Prevost repair facility.