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Old 04-18-2013, 08:57 PM   #1
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1993 33' Land Yacht
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Rear end sagging after a few days

I thought I read somewhere in the Forums that the rear end sagging could be caused by a defective inline check valve that allows the air to leak back out of air bags. I wasn't able to locate or identify any check valve under the coach. I've called Inland RV and asked if they had a inline check valve for the rear system that would elimate the sagging problem. The woman at Inland checked, and said they had the part. When I received the part it was a check valve for a water line, not air. I contacted Inland again and had a hard time communcating with her what I was looking for. I asked to speak with Andy but have been unable too. So does anyone know if such a check valve exist for the air bag system? Or I'm I getting it confused with some other part thats suspost to eliminate this sagging problem?
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Old 04-18-2013, 09:21 PM   #2
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I thought I read somewhere in the Forums that the rear end sagging could be caused by a defective inline check valve that allows the air to leak back out of air bags. I wasn't able to locate or identify any check valve under the coach. I've called Inland RV and asked if they had a inline check valve for the rear system that would elimate the sagging problem. The woman at Inland checked, and said they had the part. When I received the part it was a check valve for a water line, not air. I contacted Inland again and had a hard time communcating with her what I was looking for. I asked to speak with Andy but have been unable too. So does anyone know if such a check valve exist for the air bag system? Or I'm I getting it confused with some other part thats suspost to eliminate this sagging problem?
There is a check valve in the air system but it is between the compressor and the air tank and it's function is to protect the compressor, it allows the compressor to state against low pressure rather than against the high pressure stored in the tank. It also helps maintain the tank pressure rather than bleed off back through the idle compressor.

It you tank is holding pressure, and the check valve is holding, then the leveling valve is leaking or one of the bags or connecting tubing is leaking. Pressurize the system and disconnect the discharge tube at the compressor, there should be no air leaking if the check valve is holding. If all is good there get a spray bottle of soapy water and start spraying the rest of the system looking for bubbles. If is real quiet sometimes you can hear a small air leak. Be sure to check the exhaust tube of the leveling valves, if leaking internally they can discharge through that tube.

Good luck.
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Old 04-19-2013, 08:23 AM   #3
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Thanks for the reply. Everything you wrote makes sense, I don't have a air holding tank on my model so that part is eliminated in having to check out. I feel a little brain dead thought because I've heard the value pop up by the compressor many times,but never made the connection. For some reason when reading about the check value I pictured it to be back by the rear air bags, no wonder I couldn't find it back there. Do you have any idea on the cost for the check value and or the leveling value? Thanks
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Old 04-20-2013, 01:23 AM   #4
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Thanks for the reply. Everything you wrote makes sense, I don't have a air holding tank on my model so that part is eliminated in having to check out. I feel a little brain dead thought because I've heard the value pop up by the compressor many times,but never made the connection. For some reason when reading about the check value I pictured it to be back by the rear air bags, no wonder I couldn't find it back there. Do you have any idea on the cost for the check value and or the leveling value? Thanks
I don't know the exact set up on your coach but I would be surprised if there wasn't an air tank somewhere. The air ride systems all work pretty much the same but the source of compressed air can vary. Do you have air brakes and an engine driven compressor? If so you may be hearing the governor. If you have a 12 volt compressor like the old classic mohos you may hear the pressure switch which turns the compressor on or off. The 12 v compressors use a check valve like this. Viair Check Valve 92833 | eBay
I don't know that they make much noise.

You can contact these guys for the leveling valve. King of the Road - Height Control Valve for Suspension

Most of the valves are in the $75 to $100 range I would guess.
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Old 04-21-2013, 01:07 PM   #5
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My 92 has an air holding tank mounted near the TAG axle. I'd be surprised if yours didn't. Without a holding tank there would be too small of an air volume to compensate for rapid changes in axle position. Compressor output is actually fairly small in volume.
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Old 04-21-2013, 06:01 PM   #6
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I don't have a tag axle, and I spent a couple months on my back with it up on jacks painting and rust proofing the complete underside of chassic. I'm not the most machanical, but I never came across anything that resembling a air holding tank. I'm sure I don't have one.
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Old 04-21-2013, 06:12 PM   #7
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Maybe If you get a chance you could post a picture of your air tank. Thanks
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Old 04-21-2013, 06:45 PM   #8
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No TAG axle, then where is your air bag? Are you sure it factory AS?
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Old 04-21-2013, 09:34 PM   #9
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Its definitely factory.The air ride suspenion is made by American Carrrier I believe. There are a couple pictures of air bags and part of the suspenion on the second page of my photobucket.
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Old 04-21-2013, 10:58 PM   #10
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Its definitely factory.The air ride suspenion is made by American Carrrier I believe. There are a couple pictures of air bags and part of the suspenion on the second page of my photobucket.
The tank on my 280 is in the aft drivers side storage compartment with the compressor. It is a vertical tank about 4" in dia. and maybe 10" to 12" tall. I believe the 310's and 34.5's use a horizontal tank mounted near the center of the coach along side the frame rail. I believe they all use the American Carrier Equipment set up after 1980 or 81. The leveling valve has a delay built in so that the bags don't react to every little bump in the road consuming excessive amounts of air. I believe the change in road height has to hold for 10 or 15 seconds before the valve will react. I suppose the system could operate without a tank but it would be interesting to set up a control to tell the compressor when to operate because you would not have a pressure source ahead of the valve, that is the function of the tank. I would carefully try to follow the air tubing from the compressor to the leveling valve, the tank should be hiding somewhere in that line. Also the air tubing from the compressor control switch should lead you to the tank.

By the way your paint job on the undercarriage looks great. If you would like to keep your skills sharp you are welcome to practice on mine.
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Old 04-22-2013, 06:14 AM   #11
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What chassis is your unit built on? It looks so different from my P30. From what I can see, you have an all air rear suspension with no leaf springs. Again, very different from mine.
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Old 04-22-2013, 11:54 AM   #12
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Dan when I bought the coach in 2002 I read through the Owner Manual cover to cover. It mentioned the air tank and the need to drain moisture out of it routinely.There was a drawing showing where it should be located under the coach, wasn't there. Then as I started investigating other systems I found numerous things changed and not where the manual said should be, and the manuel stated there could be changes.I've tried to follow the 1/4" air line and have been able to follow most of it from the compressor down to the drivers side frame back to the rear air bags,and with the painting time spent under it I haven't run accross any tank.
There is a small plastic tank about the size you discribed above my compressor. This tank has no draining valve, I have air horns and from the compressor a yellow airline goes to this tank and then on to the air horn. the red air line goes to the air bags. I always figured this tank was just for the air horns, maybe this is the tank?
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Old 04-22-2013, 12:37 PM   #13
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On mine the tank is steel, about 9" x 24" long and located near the rear axle. The compressor also drives the air horns and has the same red lines for the airbags and yellow line for the air horns. The tank drain is located just aft of the rear wheels on the curb side. It looks like a 1/4 turn gas shut off valve with a short metal tube sticking out. The tank provides the needed air volume as the airbags inflate and deflate as load chages. I don't see how the compressor alone could compensate for these rapid changes but this may be related to mine only having air bags on the TAG axle. On mine the air bags are used to change the angle of the TAG axle dependent on load. With yours, the pressure may be more constant.

Does yours have rear leaf springs or just the air bags?
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Old 04-22-2013, 12:41 PM   #14
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Dan, that tank can be seen in the picture of compressor in my Photobucket pic's.
That whole bottom painting thing kinda got out of hand, I didn't start out in the beginning with plans to do the complete bottom. The project just grew, it was during the winter and we didn't have any southern trips planned. I rent a heated storage garage that I spend quite a bit of time at that I just tinkering around. I had the coach jacked and blocked up so I could clean and paint all the wheel rims and under coat all the wheel wells while the tires were off. A good friend of mine who's way more particular than me, shamed me into cleaning up the rest. I didn't think it would take that much paint or time, I was wrong on both accounts. Hardest part was applying and brushing on the Rust Kutter before painting. Now that its done I'm glad I did it, but I don't think I'll ever do another.Thanks for the compliment
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