The damn thing still sinks

[normancasson]

A little info 1st--Have a 1996 Vogue conversion a series 60 w/6 speed--had it now 2 years but haven't had a chance to use it much until now but have been a pogger for some time. The question? It naturally has a few air leaks-none in the brakes, they'll hold for weeks-that I'm trying to find. When the aux air goes down it exausts the rear axle-usually takes 45-60 minutes. Sure I could just keep running the aux compressor but its loud and not one of those things I like to do in a camp ground. Also w/an air toilet it also quits working--sovled that problem by isolating it w/its own small compressor. Now for the real question---Prevost makes a kit to solve this problem by I think rerouting the air system. I just left Nashville and they gave me an estimate of 3,143.34 to install a"tag axle logic" kit so solve this problem. The estimate was 1,055.14 parts & 2,088.20 labor. After getting the estimate I had a part number so I walked into the parts dept and got a price of $780.00 for the same part.My question? has anyone had this done? If you did-did it work well enough to justify the cost? My understanding from someone in the know was it only takes 2-3 hours to install. If I can find it really works it would sure be worth it to me. Anyone had this done? Thanbks-Norm Casson

[dreamchasers]

My coach had the same issue when I first purchased it. Very frustrating! The issue only affects coaches in the 1995-1996 age. What actually happens is when the aux air system leaks down, the "control signal" to the Norgren valve that controls the tag axle drops to a point that the Norgren transfers and the tag axle is released, thus the rear will sag. I looked at the revision kit and decided it was much easier and significantly cheaper to tighten up the aux air system. It took time and effort, but now my aux air compressor runs once every couple of days. I consider that tight enough for me.

Good luck on the diagnoses and repairs. Taking it to a Prevost service center "might" solve the problem, but be prepared to pay the price. Failure items on my coach included a pneumatic air tensioner in the engine bay and the regulator that supplies it. Their are so many spots that can cause aux air leaks, it would impossible to cover them all in this post. Several POG members can offer tips for places to look for leaks. Rubber is the enemy of these older coaches.

If the tag axle releases within 60 minutes, you have a very significant air leak and it will be easier to find. I use a hand squirt bottle with soapy water to find leaks. Also, I use a home made leak detector that works for me.

It can be frustrating dealing with air leaks, but my bus is evidence that you can tighten up the air leaks. If you are going to do this work yourself, you will need to learn the pneumatic system for your coach and isolate it one segment at a time.

Where do you live?

Hector

[truk4u]

It's actually called "reverse tag logic" and the price Prevost quoted you is about right. My 94 Liberty had the same system and like Hector, I just spend all my time reducing the aux leaks. The fix is quite involved and once I had a breakdown of the parts, there were many, I understood why it was labor intensive.

Sounds like you have a bad leak in the aux system and there lies the problem. Don't let anyone kid you about a quick fix for reversing the logic, it has to be done right.

[Jon Wehrenberg]

Norm,

Hector is correct on many levels. My 87 had the same system design and when the pressure dropped the tag axle air was dumped and the rear sagged. So I set out to do what Hector did and that was to eliminate all leaks.

It can be done. But plan on doing it yourself because everything that uses air in your bus but the brakes is on the aux system and the places for leaks are only limited by the number of fittings and devices on the system. In my case my suspension system was the biggest culprit so I quickly learned that our air bags and the Norgrens in the system have about a 10 year life (if lucky) and after that they contribute significantly to leaks. I rebuilt the Norgrens, bench tested each one and replaced them. I replaced all the air bags. That made a significant difference because that coach had an automatic feature for leveling that functioned with the key off. The suspension on your coach should not function with the key off so unless you lean quickly that should not contribute to the compressor cycle time. But I also found leaks in the air tensioners, the pressure regulator for the air tensioners, the driver's seat, and other places I cannot remember. I worked for weeks and got it to where the compressor would run once a day. At that point I quit. A help in searching for leaks is being able to isolate devices, plugging their supply so if they leak you eliminate the leak to see how pressure holds. When I did my current coach I put in valves so I can turn things off one at a time to see which leaks.

I did the same leak search with my current coach, but now four years later I should do it again, but since my suspension system does not dump tag axle air I am just going to leave the switch for the air compressor off. The only things I really need air for are to dump the tank or to get under the bed and as often as I do either I will just turn on the compressor.

BTW, The leans are starting after redoing the valves and air bags 6 years ago. But since the leans do not show up for about 5 or six days I am not planning on addressing that issue either.

There is no single way to find leaks. You may find a soapy solution, a stethoscope, your ears, or an ultrasonic leak detector may work best. Internal valve leaks will not show up with soapy solution, but may be found easily with an ultrasonic leak detector. If you get really frustrated Jim Shoen used refrigerant in the system and found leaks using a leak detector. That is not advised because the refrigerant oils may adversely affect the O rings and gaskets, but if all else fails it is an option.

Good luck.

[normancasson]

Gentleman thank you-
I forgot to tell you per advice from a former pogger I tried to outsmart the system. By simply rasing the tag after parking the darn thing doesn't drop except for that initial instance when you put more weight on the rear axle when the tag is lifted. Being a west coaster I haven't had many chances to go east since the first Kerville rally but my daughter is a military wife whose husband is stationed in Ft. Knox. Ky--
She presented us with our first grandchild 9 days ago and I wasn't missing this one. I'm currently staying in the Military campground there-not exactily an outdoor Resorts but well enough equipped for a short stay. I decided to stay until the end of the month so I could attend the RVIA show in Louisville--I'm not going to attempt to fix anything on the road but will wait until I get home---I've already been through the system a few times before leaving home-gone through a few bottles of soapy water and fixed quite a few leaks already-you'd think with it leaking that quickly any air leak would be easy to find but its probably going to be many small ones all contributing--I don't have access to a pit but that would probably make things easier. If didn't think any of the 2 strokes had the same system....As some of you may know I'm still a TBC member also having an 87 Marathon and I never had this problem with it. I'd just like to get my hands on the installation instructions for the modification kit to see how tough it is to install--since I'm rumming my toilet off a separate compressor (I also did this on the Marthon) I really don't have anything else needing air when I'm parked.

[stevet903]

Ask and ye shall receive:

http://prevostparts.volvo.com/technicalpublications/pdf/Sb96-14B.pdf

I did the mod on my 89 XL - very easy to do once you identify the pieces - just swapping of airlines to different ports, and adding a relay into the electrical panel. It works as advertised. Reading the doc, I was glad I didn't have a later model, since it gets considerably more complex than what I had to do, and requires welding a bracket on to hold an inversion valve. Hope this helps - Steve

[Jon Wehrenberg]

Norm,

The reason is does not drop is because by lifting the tag you have already dumped air from the tag axle air bags. If you can try to isolate each device such as the driver's seat, air horns, generator air bags, etc. As you plug each system so air does not reach it you can tell which is leaking and then can concentrate on sysyem. I start big and then get more detailed. For example, on my coach the converter's systems get their air off the aux connection in the steer bay. By plugging that I know if the Prevost aux devices such as the door lock are leak sources.

But here is something to ponder. Apart from having a nice leak free aux system, how will your use of the bus change? When possible I just dump air in a campsite (assuming it is near level) making it easier to step up that first step to get in the bus and to eliminate the need to level it or use air for anything except the stuff I mentioned above. You could do the same thing and as long as your toilet has its own air system what does it matter if the auc pressure goes to zero? It's heresy to suggest ignoring a problem, but as our coaches age and the rubber parts age also perfecting the system becomes an increasingly greater challenge.

It would be so easy if air leaks were always single isolated issues, but they are often a combination of small numerous minute leaks that occur over time making them painful to find.

[JIM CHALOUPKA]

Ask and ye shall receive:

http://prevostparts.volvo.com/technicalpublications/pdf/Sb96-14B.pdf

I did the mod on my 89 XL - very easy to do once you identify the pieces - just swapping of airlines to different ports, and adding a relay into the electrical panel. It works as advertised. Reading the doc, I was glad I didn't have a later model, since it gets considerably more complex than what I had to do, and requires welding a bracket on to hold an inversion valve. Hope this helps - Steve

Thanks Steve this is interesting and informative to say the least, for the record I am not very interested in making the upgrade/mods at this time and will maintain my bus in the original configuration for now.
My bus is on the list near the end with T1025710.

JIM

[michaeldterry]

But here is something to ponder. Apart from having a nice leak free aux system, how will your use of the bus change? When possible I just dump air in a campsite (assuming it is near level) making it easier to step up that first step to get in the bus and to eliminate the need to level it or use air for anything except the stuff I mentioned above. You could do the same thing and as long as your toilet has its own air system what does it matter if the auc pressure goes to zero? It's heresy to suggest ignoring a problem, but as our coaches age and the rubber parts age also perfecting the system becomes an increasingly greater challenge.

It would be so easy if air leaks were always single isolated issues, but they are often a combination of small numerous minute leaks that occur over time making them painful to find.

Like Jon, I normally dump my air when parked on near level sites to make it easier to enter/exit the bus; to eliminate the need to engage the HWH leveling system; and to eliminate the need for the aux compressor to run (which it will do often if left on). However, my leak "status" is at the severity level that my belts on the engine go slack after about a day and I have to remember to turn on the aux compressor and let it run long enough to build enough pressure to tighten the belts prior to restarting the bus engine for fear of "throwing a belt" on start-up. I'd love to be able to eli8minate this concern by tightening up my systems and lessening the air leaks, but I'm clueless about where to start and how to do it! (read that "lack confidence in my ability to do it"). :o Is my fear of starting the bus with the belts slack unfounded?

[Jon Wehrenberg]

Two comments........I have read where slack belts will be thrown. I often start my coach with belts that have gone slack and I have yet to toss the first belt.

Seated coaches are configured like ours as far as the engine and belts, but they lack an aux compressor. If slack belts were an issue that would have been dealt with long ago because seated coach operators are not going to stand for that kind of an issue. They have no way to tighten up the belts and you can bet their aux air goes to zero.

The second comment is any coach that has had leaks ignored forever is going to be a serious challenge bringing it to a near leak free status. If that is the goal the owner should plan on spending hours and hours checking every fitting and device and system, or plan on mortgaging the house if the responsibility is turned over to someone else. It is a difficult time consuming job that requires absolute attention to detail.

[Ray Davis]

At POG 9 someone mentioned a liquid that is used to find leaks in refrigeration equipment. Evidently you had to purchase from an A/C company or technician. Anyone remember what it was called? Something "Blue" I thought.

Ray

[GDeen]

just as an aside, when I first got my bus, the belts would stay tight for days, even weeks....after a few months, a leak developed such that they would go slack. It never caused any real problem, as Jon says never once tossed a belt, but it still bugged me. Couldn't find it even though couple of times I thought I had through lots of soapy spray.

Well while working in my webasto compartment shortly after shutdown recently I heard a leak and sure enough, it was the air line to the back bellows. Repaired and now my belts stay tight for quite some time. I just like the notion of an air tight system whether it is practical or not.

As to Ray's comment above, that was Country Coach Miles who mentioned the commercial product used for finging refridgerant leaks I believe....

[stevet903]

There are several leak detector solutions out there - I've used this one and it works well:

http://www.nucalgon.com/products/gasleak_detectors_calblueplus.htm

There are others out there - here is a good paper on leaks and leak detection from the company that makes Big Blu:

www.refrig.com/Product/Manuals/LeakDetectionManual.pdf

or you can make your own with dishwashing soap and glycerine:

http://www.ehow.com/how_5993424_make-leak_detection-soap.html

Steve

[Ray Davis]

Thanks, Steve!

[normancasson]

Thanks to all who came up with some great suggestions. I've decided #1 that I sinply need to get it back to the condition it was in when it rolled out of the factory--fix'em all...but I also recognize that Prevost themselves were a little short on the engineering side and the bus should also be in the condition it would be in if made today. I'm currently a long way from home so will wait until I return when time will be on my side.....besides now I've discovered the Splendide unit washes fine but doesn't dry at all......Oh well, the joys of RVing just keep coming.

[Woody]

FWIW my Splendide didn't dry - I pulled it out and found that the hot air exhaust hose had collapsed. Replaced this and after destroying a good bit of formica sliding (?) it in and out it works just fine.

How does one match 20 year old formica -------

[truk4u]

Norman,

If you get a chance, please add a signature to your posts with bus info.

Thanks...