Air Bag Replacement

[dale farley]

I brought my bus home today to do some maintenance. As I had discussed in a previous thread, I had a significant leak in my right tag axle air bag. It took about 1/1/2 hour to replace it, because I wasn't really sure about the procedure. But I got it done and everything seems to be fine with the installation.

The bus still drops on the right side when I turn it off. Before removing the tag wheel, I placed 4" of plywood under all 4 of the drive wheels, so it would be off the ground a little. I then placed 2 jacks under the right side and jacked it up enough to make sure the bus wouldn't come down too low with me under it when I drained all the air. Every time I turn off the bus, I hear what sounds like air traveling through a pipe. It is very audible in the area where the front drive air bag and ride height valve are located (see attached picture). I have checked every fitting with soap, my ultrasonic leak detector and a hose (cheap stethoscope), and I can't find a leak. As the bus drops on that side, the noise subsides.

Now that I am out from under the bus, I am wondering if this could be caused by the fact that I still have the right side of the bus jacked up a little bit? The wheels are not off the ground, but it is sitting on the jacks. Could the ride heigth valve be trying to level the right side or does that valve even work when the bus is shut off?

I would go back out and let the jacks down, but it is dark and cold, and I have to jack the bus up again Monday so I can change the Air Dryer cartridge. Sorry for the long post.

[Orren Zook]

Roadrunner,

The leveling valve you show in the picture is mechanical, and would continue to seek level even when the ignition is turned off. If so, check the little hose at the top of the valve (there should be three ports on the side where the leveling arm is) to see if it is exhausting air when you hear the sound described. You've got a couple of variables too, 4" of wood under the drive axle and the right side of the coach jacked up, both of which should cause the leveling valves to operate seeking to level the bus.

Make sure you watch for pinch points while you're under the coach checking this.

[dalej]

Dale if you start jacking on the bus you will let old air out of the valves but new air won't replace it until
the key is in the on position. As you can see in the photo the leveling valve goes through a solenoid that
is run off the 24v, so the key has to be on. Hope this helps....we have this thread somewhere on this site.

[Joe Cannarozzi]

Roadrunner, sounds like that is exactly what is going on. When that ride-height valve begins to function 2 things happen. First there is a delay built in. Second it will adjust very long and slowly. As previously suggested you'll feel the air coming out the exhaust port, a short small tube hooked up to nothing.

[Jon Wehrenberg]

Roadrunner....sorry to disagree with our fine associates, but the ride height valve that was pictured WILL NOT FUNCTION WITH THE KEY OFF.

I have emphasized this before but it needs repeating. Each converter has their own way of handling the leveling of our coaches so we cannot get too specific here, however I have never seen or heard of any Prevost with a level low system that had functioning RIDE HEIGHT valves with the key off.

We can get into a discussion of the general procedures for isolating a leak that allows a coach to lean, but first I wanted to correct the misconception.

However....if that valve leaks it is possible for the coach to lean. If it is leaking the air will escape from the six inch plastic exhaust tube as Joe points out. He also point out about the time delay so be very careful before you put yourself in harms way to insure the coach cannot drop no matter what happens.

[Jon Wehrenberg]

Dale you are correct but if you look closely at the photo I think it is a Norgren valve controlling the air supply to the ride height valve. Depending on the converter it might be pneumatic.

[Joe Cannarozzi]

That ride hight valve Will let air out of that corrisponding corner with the ignition off. I just went out and disconnected the linkage arm to check it and I got Air to exhaust and there is no key in the ignition.

I know there is an electric solonoid that isolates things when the ignition is off and I'm sure that I can not raise that corner with the ignition off but it can be lowered with the ignition off. So if the frame was jacked higher than normal ride height while servicing it that ride hight valve on our bus under those conditions, would allow air out with the ignition off.

One disclamer is that our bus does not incorporate these norgrin valves. Don't know the first thing about them.

[Jon Wehrenberg]

Joe,

My second paragraph above emphasizes that different converters did different things and on this forum we discussed your coach IS different. The fact that you do not have the Norgren valves I think separates you from most if not all other coaches on the forum.

If the ride height valves continued to function with the key off, then the minute you leveled your coach and turned off the key, the valves would be trying to bring the coach to the position dictated by the ride height valves, and I don't even think your coach does that.

We can only make broad statements about leveling unless the posters have specific converter information and knowledge and it is clear their topic is related to not only a specific converter, but in some cases a model year or coach style. For example my Elegant Lady may be different than a Classic of the same year.

[rfoster]

Roadrunner: As Jon had mentioned we have changed all 8, yea 8 of the air bags on our two coaches. His did great. Mine is still laying down in front overnight. Jon checked with his new hi tech ultrasonic leak detector and in less than 30 seconds located a Norgren valve in front steering compartment leaking past the spool inside the valve (no way to detect with bubbles). I have not replaced it has yet (still working for a living or for the gov't) but will at my first opportunity. This doesn't fix your coach but may give you a bit of satisfaction in knowing chit happens to the best of us. I did have an air bag leak on the left front due to age, a pinhole had developed ,it was time to replace them all, I was in hopes that would cure the problem of the leans. A work still in progress.

[dale farley]

At first, I didn't think I had Norgren valves, but I have since verified that I do. As shown in the picture, there are two different Norgrens in my steering compartment.

Jon, I am not sure if there is a Norgren in the area with my ride valve. I assume you are talking about the valve that appears, in the picture, to be on top of the ride valve. I was thinking that was an integral part of the ride height valve, but I don't know. The only other component I see is what appears to be a small manifold on the right side of the picture.

I hope to solve this puzzle tomorrow if it stops raining. I will check to see if I get the same noise again, then I wil remove the jacks and see it it repeats itself. I am hoping it will go away.