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uneven lowering
I have had a problem with a right side lean for years, Hector was in mine driveway last year and we fix many leaks. I replaced all the air bags, all the norgren valves in the rear. Now my issue is if I let the bus deair and then dump the tag on it’s own the right side will drop lower then the left. If I go into the coach and turn the key on and try to lower the left side with the low level system it will not drop anymore than it has already has done. If I air up and then drop the rear on both sides with the low level system it drops down evenly and then the tags deairs the next day and the coach squats evenly and stay even. What could hold up the left side if I don’t purposely lower the rear?
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6 Replies
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Greg,
If your aux air pressure is less then 30 or 35 PSI none of your Norgren valves are likely to shift as you command. I think your coach system logic requires aux pressure to hold the 3 port valves between the tag and drive axles closed against spring pressure and their normal position. If the aux drops below 30 to 35 PSI those two valves should open and dump tag air. When I say open on those valves I am saying they close the path between the drive and tag air bags and open the path to exhaust tag axle air bags.
If one side does not drop like the other I would question whether that side’s 3 port Norgren is functioning. It might not be shifting possibly due to internal corrosion. When you manually lower the rear the 3 port valves in the rear are maintaining the air path between all three air bags on each side and air is exhausted out the three port valve in the front.
Hector may want to jump in here because of his recent experience with your coach.
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I think Jon nailed it, sounds like the problem is in the tag logic.
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I think Jon is spot on, with a twist. My experience has been when attempting to manipulate the rear air bags (left/right) with the manual controls with the aux air pressure low, unpredictable results can occur. Remember, on your model Prevost (and mine), the pilot air for the tag axle solenoid (the solenoid that blocks the air between the main drive air bags and the tag axle air bag, and vents the air) originates from the aux air supply. So if the aux air is low, its any body’s guess what the actual position is.
Concerning Jon’s statement of 30-35 PSI aux air pressure being the trip point for the tag axle control to release, I am one that thinks that pressure is a wide range variable. Meaning, since this air pressure supplies a pilot valve (spool position) in a Norgren valve. Exactly where the tag axle spool is with regards to valve air ports can only be an educated guess.
My suggestion is if all suspension controls operate properly at normal operating pressure, all is OK. Greg is a very detailed individual, my bet is all is in good order.
Let us know if anything else comes up concerning this.
Hector
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I believe Hector to be correct about the variables. The aux air is holding the 3 port valve open to retain air pressure in the three rear air bags. When the pressure drops below a value needed to hold against the valve spool return spring that particular valve exhausts tag air. The variable is the amount of pressure to hold against the spring might be different from side to side because of internal valve friction and the amount of force the spring exerts. In a perfect world both rear three port valves would shift internally at the same pressure.
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Thanks guys, it makes prefect sense that I could not exhausted that left side with the low Aux tanks pressure. Since I replaced all the norgrens and the air bags I need to find out what happens first. Does the coach drop one side then the aux pressure drops and dumps the tags then blocks the air in the left drive bags. or does the coach have more or less pressure on one side than the other causing one side valves to shift early than the other or does one side leak faster than the other and it is closer to the ground when the aux run out of pressure blocking the norgrens. ??????????
Thanks for the challenge.
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My guess is the drop of aux pressure begins the series of events. What sequence those events takes is probably repeatable.
I am assuming there is nothing out of the ordinary to affect what would be an expected sequence. I say this because on two occasions now I have spoken with owners who have had problems that did not make sense and in one case several years ago the problem originated because a valve had hydraulic lock due to water in the system. Trying to make assumptions about problems is often frustrated by having the unexpected be the root cause.
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