Stands

I have been replacing the air bags in the rear of my bus and I have the bus up on Jon's stands. The other day I was working under it sit behind the differential when the for some reason I heard and felt air coming out of the one Norgren (I think the top one) and all three bags on the drivers side went empty. PANIC. But the bus didn't drop because of the stands. You never know what may cause the suspension to drop.

I could understand why the tags would dump air if the pressure got low, but all three bags on one side? The passenger side three bags were still rock hard. The bus is level on the stands so I don't think it has anything to do with the road leveling controls. Level selector was in Drive and the key was off.

That is Scary but its great to know when your safe from such a failure. Will you replace the norgren?

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Originally Posted by gmcbuffalo

I have been replacing the air bags in the rear of my bus and I have the bus up on Jon's stands. The other day I was working under it sit behind the differential when the for some reason I heard and felt air coming out of the one Norgren (I think the top one) and all three bags on the drivers side went empty. PANIC. But the bus didn't drop because of the stands. You never know what may cause the suspension to drop.

I could understand why the tags would dump air if the pressure got low, but all three bags on one side? The passenger side three bags were still rock hard. The bus is level on the stands so I don't think it has anything to do with the road leveling controls. Level selector was in Drive and the key was off.

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Very interesting!

If you heard air escaping from one of the five port Norgren mounted on the forward bulkhead, in front of the differential, during this deflation of the airbags, then the Norgren either intermittently failed or the pilot valve in the pneumatic cabinet failed or gave the signal to the Norgren to dump the air. I am one that believes the Norgren valves used in our busses are very high integrity valves. If you look up the specification, the number of cycles are rated in the thousands (can't remember the exact number). Far greater than the usual RV owner will ever cycle the valves. The biggest issue I have found is that after many years of operation in the hostile environment under the bus, the o'rings will shrink and leaks will occur.

Concerning the leak, if your Prevost is of the vintage that when low aux pressure results in a tag axle release, then their will be a momentary lose of air pressure. But it should not have deflated the air bags completely?

The best thing is you had you bus sitting on Jon's jack stands. I use mine anytime I crawl under the bus, every time! I carry mine in the rig. Of all the tools I have acquired for the rig, the jack stands are rated at the top of the list. Jon should get the POG "Safety Award", if we have one, at Austin.

Thanks Jon for taking the time and effort to build the Jack Stands!!!

Hector

Jon,

I was missed out getting a set of stands from your last production run. Are you willing to consider another production run if enough of us are interested? OR, will you sell a set of drawings that could be taken to a welding shop for fabrication?

John

Can these Norgrens shuttles be serviced without taking the Norgren body off the frame?

I recently replaced all of the under-chassis Norgren valves in our 98/99 Royale. The bus has always been garaged but lived in the south for the first 10 years of its life. I found all of the valves badly corroded and the O rings brittle. One of the front Norgrens had failed internally. Norgrens are a simple, all aluminum spool type valve with very little to go wrong. Corrosion and age however can be their downfall.

Thanks Jon, for your suggestions and warnings in reference to changing rubber dependent components around the 10 year mark. Preventative maintenance starts at home where it's a lot cheaper and more convenient to get done than on the road.:)

Greg, Norgrens can be overhauled but in my opinion its more trouble than its worth. I can't imagine you could do so without removing them from the coach. They can be purchased locally but the savings was minimal.

I consider Hector the auxiliary air genius of POG. I will add my 2 cents to this discussion and hope he jumps in here.

Low aux pressure should not result in air dumping on one side (I don't think). If my theory is correct it may be that the loss of aux pressure allowed the Norgren on one side to dump air, but the other side for whatever reason did not shift due to the low pressure. If might be because the Norgen internals are not moving smoothly and as Brian pointed out could be corroded.

I did rebuild my Norgren's on the first bus, but it is soooo much easier just replacing with new. Corrosion internally will mandate a new valve because the rebuilt valve with internal corrosion will never function satisfactorily.

Greg,

As Brian mentioned, its seems simpler to replace the entire valve when needed, thus assuring all components are new. A comment worth mentioning, when reinstalling the pneumatic fittings into the new Norgren valve assembly, take extra precautions to assure you use thread sealant to assure you do don't create minor leaks in the fitting connection. Jon has stated that he prefers using a liquid thread sealant and has good experiences with it. I have used Teflon tape for many years in industry on connections involving hydrocarbons gases with success. I think both type of sealant work satisfactorily.

Let us know what you found leaking? With the complicated suspension systems and aux air systems on our coaches, any knowledge of potential leaks spots is a benefit.

Good Luck.

Hector

I noticed this one sided thing after changing the bags and thought it had something to due with the ride height valve. It does it even with good Aux air Pressure. Yesterday the drivers side was deflated and the Passenger side Up. So I dropped the aux air down to 20 PSI and waited about 5 minutes later the Passenger side tag dumped. So I think I have a bad Norgren. Mine are almost welded to the frame I could not get them off when I was changing the bag without the thought of damaging them. Maybe I did. Those tubes in and out are so short and ridge I thought the best way was to take them off. No way. A year ago I changed the air dryer who know when and if it was done before. So replacement sounds like the best option.

When replacing a Norgren you obviously need to do a leak check on the fittings. But I have learned that I can save myself a lot of grief if I bench check the new valve before I install it.

I just used a bunch of fittings that I could thread into the new valve on my workbench and apply air pressure at the various points to verify the new valve will work and is leak free. Should the new valve have even a minor leak it drives you crazy trying to sort out why the bus leans or loses air, especially when all the fittings on the bus to the valve are leak free. If you are just replacing one valve it is less frustrating because you can zero in on that one valve, but if you are changing out all the valves at once it eliminates the risk of having to figure out why the bus with new valves is still leaning or losing air.

As to keeping the air system dry, that is a little bit of preventive maintenance that pays huge dividends. The cost to change dryer elements every year or two (I use two year intervals) and to drain all the tanks every time you get under the coach keeps the inside of the Norgrens clean, shiny and dry and eliminates many problems due to moisture. I know of at least two coach owners whose poor air system maintenance resulted in a Norgren having a hydraulic lock which makes diagnosis of any problem much more difficult.

I am thinking the 3 port valve that separates the drives and tag is stuck the the 3 bag position. Or do you think we are dealing with the 5 ports on the bulkhead? I hear the air escaping back by the two 3 port valves.

Internet diagnosis is difficult because normally when solving issues we use all our senses. On the internet we lose the ability to hear, see, touch and smell so all answers have to be treated as shots in the dark. I will answer the question with some assumptions.

I am assuming the 3 port valves have some age on them and I am assuming the air system has had some internal moisture. That leads me to believe there is likely no one single problem but a probable comination of problems which will make a solution and answer suspect. If the aux air system has in fact retained moisture the valves can have internal corrosion which will not only make them leak, but will in all probability prevent the spools from sliding when pneumatic or spring pressure is applied. As a result the three port valves between the drive and tag can be exhausing air, but the corresponding 5 port valves and the three port exhaust valve in the steer compartment can also be failing or failed in the same manner.

The net result is even if the 3 port valves in the rear are replaced, the other valves are in the same condition and you can experience inconsistent problems until the entire system is repaired. I know from seeing valves that have been removed from coaches that internal moisture will ultimately bind up a valve and when that happens a problem diagnosis almost requires a step by step examination of every valve and device in the system, starting with verifying there is power to the solenoid coil on the mainfold, and then following the air flow from the solenoids to the pneumatic operators and then to and from each valve.

While the ride height valves (not to be confused with the Norgrens) are very reliable, they not only can be leaking also, it is entirely possible one or more can be receiving air from the five port valves because those valves are not functioning correctly. I found this condition on Michael's coach and even though he had properly maintained his air system, the previous owner had not and the internal damage was widespread necessitating all new valves. In diagnosing Michael's coach suspension problems several things did not make sense because the valves just were not doing what they were supposed to do.

My recommendation is take any suspect valve apart (you will likely break the screw heads off due to age and corrosion) and if you see any evidence of white corrosion assume every single Norgren, all ride height valves and all solenoid valves need to be replaced and the entire air system needs to be dried out. A poorly maintained air system is not only going to get moisture in it, but it is possible oil from the air compressor has also made it past the air dryer and wet tank and is also adding to the crud within the valves.

Greg, ZERO out the air system with all new at one time. That will likely last your lifetime.

If after that you are still inclined, take your old valves apart to inspect and clean and rebuild and you might find one or two that you can save for spares. (I find this can be fun and interesting but truly not worth the time)

IMHO don't contaminate your new equipment by mixing with old.

Don't forget, "pay me now or pay me later, but your going to pay"

JIM :)

Thanks Guys
I'll get on it