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air ride system problems
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Hello Jerry
i don’t think so it looks to be a factory installed system.
I think we have tracked it down to the rear norgren valves. -
If Royale used a JunnAire Compressor on the unit, check the JunnAire compressor oil water separator to be sure it is clean and empty. The JunnAire used SJ27 il and the oil will eat anything close to rubber or plastic.
If it has a JunnAire I would suggest changing it to a California Air compressor to get rid of the SJ27.
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We need to start another thread to discuss pneumatic system moisture prevention.
The Prevost system when properly maintained works well and provides air as dry as the Sahara, But no converter, none, nada, zip, not a one has provided one of equal quality and capacity for use with the aux compressor that feeds the coach accessory system.
The worst part is how much each converter’s system will vary from the next so there is no single best solution to keeping air from the aux compressor dry and out of the accessory system.
Adding to that is most owners are not even aware of the problem.
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Hello!!!
I found the problem and it is now working properly in drive mode. After all the help from Jon and Don and few others I was convinced that the drive mode norgren valves were not opening as they should but not knowing the real reason why. I checked the number 3 coil out a couple of times thinking it was working and it had small amount air coming out of 3 that activates the drive mode valves but not near as much air as the 5 coil log had going in. So I removed #3 coil and valve and tore it apart to find a small piece of debris blocking most of the tiny center air passage. I cleaned it up and reinstalled and BA-BAM it worked and bus is sitting at 11” all four corners.
Ok update lol the bus sits at 11” for 6 minutes not running and then air is dumped in the rear somewhere right a 6 minutes and the bus drops down 2” if the bus is running it stays up no problem. I engaged the tag lift while is was running and air is released somewhere around the tag and drops down a few inchs and the tag did not go up that i could see. Should the tag come off the completely off the ground when engaged and how far?
Thank you all for your help!
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Thank you Mikee!
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I’m still not clear if you have the tag logic or not, if so, then you likely have an aux air leak that you should be able to hear with the engine off. I assume the 6 minutes until it drops is because the logic dumps the tag as the aux air leaks down to a low number. If the bus is running, the compressor is keeping the aux supplied with air and it stays up.
None of the 45′ I had would lift the tag, the 40′ would. I know some 45′ will lift the tag, but it has to set for a really long time with engine running.
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Hi Tom!
I jacked up the bus and jack standed it real good, I started the bus and let it come up to ride height and shut if off. I climbed under and waited a few minutes and the tag norgren valves both opened and dumped all the air out of the tag bags. The drive bags stay up only the tag dumps so the tag valves must shift open at a certain psi but i would think they should stay closed?
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crafty b, here is a PC thread link you might find useful about the 5 stack, its armatures, and coils.
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Thanks Don!
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crafty b, here is some air ride and leveling system info from “PrevostService” I keep in my logbook that you might find useful.
Burketts valves were what Prevost used in the mid to late 90s as a replacement for the Norgren three way valves. They come either NO or NC and they cannot be altered. The first versions of the valves did not have a return spring in them and we had numerous issues where the valve would stay in the midway position. This led to air systems not building air correctly. Normally the bad valve was on the tag lift system and by simply cycling the system you could get the valve to seat itself and the air would build correctly. Burkett came out with a valve with a return spring ( the new Burkett valve) but we went back to Norgren valves eventually. Another issue with the Burkett valves was they were made for a much cleaner, industrial application. The coach pneumatic system in not a completely clean and dry environment. The Burketts did not fair well on the coach. The Norgrens were more robust and did not mind a little oil and water in their working environment.
Most of the people in Prevost service do not know anything about the Norgren numbers. Prevost parts secures the correct Norgren number for the application from the engineering department and then a Prevost part number is generated. To get the Norgren number we would have to get someone in parts to look at the cross reference file for the correct Norgren number. That is why you may get a blank stare from a tech if you come out with a Norgren part number.
As noted also above the type of valve you need (NO or NC) will be dependent upon your pneumatic configuration in the rear of the coach. Up through 1996-1997 the plumbing of the tag axle lift circuit required that there be sufficient air pressure in the auxilary air tank air sytem to properly pilot the valves associated with the tag axle and tag lift system. Thus you needed good aux. air pressure to keep the coach at normal ride height in the rear of the vehicle. Lack of proper air through an air leak would eventually reduce pilot or control port air pressure to the point where the internal spring tension of the valve overcame the control pressure and the system cycled much the same as if you had flipped the tag lift lever. The difference being that there is no aux air pressure left to do anything with the system.
Engineering at Prevost redid the pneumatic “plumbing” of this circuit in 1997 so that there were no control pressures to any of these valves to keep the tag axle down and the tag lift circuits off. There was a maintenance bulletin released “Service Bulletin 96-14B) to increase the reliability of the pneumatic system. The bulletin can be found at https://secure5.volvo.com/technicalpublications/pdf/SB96-14B/pdf. There were various kits made at the time for different models. These would come with instructions and valves that had the proper brass fitting for the application. The kits also included an inversion valve that had to be plumbed into the circuit. Prevost has always cancelled the brake boosters on the tag axle when it was lifted to prevent tire damage. As we were changing the way the axle was controlled we had to change the control of the Bendix R12 valves that controlled whether there would be brake application pressure sent to the boosters on the tag axle or not.
The modification takes some time as the old valves need to be removed and air lines properly identified. Then the new valve installed correctly and the inversion valve installed. Plus the light circuit in the dash had to be changed to reflect the lack of air pressure in the controls when the vehicle was in the normal ride height position.
All that being said: to check your system! Run vehicle and get all air tanks filled. Turn off coach. Open accessory (auxilary) air tank and bleed down the pressure. If the coach has the newer system installed the vehicle should NOT settle in the rear as if you flipped the tag lift lever. If if does squat, then it most likely did not have this modification done.
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Crafty,
As soon as you shut off the bus, what’s happening at your aux air gauge in the steering compartment?
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I hope his bus has an “aux” air gauge? My bus didn’t come with one, so added 2, so I would know what is what with the system.
Crafty b, does your bus have an aux gauge?
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Good Afternoon!
the bus will sorta hold air pressure on both dash gauges, it sat overnight and it has 70 psi on both now
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There a 2 psi gauges on the dash and one on the electric air compressor, the electric compressor works and pumps up to 100 psi and shuts off but there is a dandy leak somewhere and cycles every 10 minute or less. I will need this to not leak with a vacu flush toilet system. Not even sure where to begin on looking for that leak.
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