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another potential problem! Why my air bellows are low? [message #227219]

Sun, 27 October 2013 13:46

budworks521

Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...

Karma: 4

Senior Member

I have been working on my engine and jacked up the center front cross member for one day about 8 inches or so. After awhile upon letting it down I noticed my rear suspension was lacking height. I have the batteries undone, have not run the engine for over a month, and my grade in back is slightly sloped backwards compared to the front. When you look at the bellows they seem like they are holding air and was wondering what I might have done. I have since jacked the back and supported the framing to keep the angle of the bellows and pressure points more equal. Is it possible to close the valves before the bellows and pump compressed air into the bellows to straighten them out? They have shutoff valves and then an air inlet valve just before the bellows. Are these air valves used for pumping more air into the bellows if your system is down? Yes I am a bonafide rookie!!

1974 Painted Desert 455 upper half rebuild constant project inexperienced mechanic Grand Rapids Mi Always trying to learn

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Re: another potential problem! Why my air bellows are low? [message #227227 is a reply to message #227219]

Sun, 27 October 2013 15:06

George Beckman

Messages: 1085
Registered: October 2008
Location: Colfax, CA

Karma: 11

Senior Member

budworks521 wrote on Sun, 27 October 2013 11:46

Is it possible to close the valves before the bellows and pump compressed air into the bellows to straighten them out? They have shutoff valves and then an air inlet valve just before the bellows. Are these air valves used for pumping more air into the bellows if your system is down? Yes I am a bonafide rookie!!

You didn't mention in your signature what year coach you have. In general, the air bag (I love the term bellows) system does often have tiny leaks. For some unknown reason, our coach is currently holding air, but that is this month. Ha.

The valve near the bellows is to isolate the bag from the tubes, valves and compressor and on many coaches, an air tank. Alas, sometimes the coaches still sag when the valves are off. The bag or bag connection might have a tiny leak.

We have a 74 with the compressor in the front and a gallon or so air tank. The air tank seems to loose air and fairly quickly... two or three days. I cannot seem to find that leak. But from the leveling valves to the bags there seems to be no leak.

Sometimes a shrader valve is added at the bag so you can put air in with a compressor much like you would put air in a tire. On my coach that valve must be open for air to flow into the bag.

If, when you jacked the coach up, the air bag got sort of deformed, that is usually not a problem. When you put a new original style bag in, it twists itself into the most horrible shapes and then suddenly pops into perfect alignment.

Hope this helps.

'74 Eleganza, SE, Howell + EBL
Best Wishes,
George

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Re: [GMCnet] another potential problem! Why my air bellows are low? [message #227229 is a reply to message #227219]

Sun, 27 October 2013 15:08

USAussie

Messages: 15912
Registered: July 2007
Location: Sydney, Australia

Karma: 6

Senior Member

Lawrence,

First of all you haven't created a signature that contains your GMC year and model and where you are and since there are three
different types of rear suspension systems I (we) can't provide a proper response.

Next I would suggest that you read the Operators Manual for your GMC which will give an overview of how the system operates and what
the setting should be.

Finally I would suggest that you go to the Rear Suspension section of the Maintenance Manual and read how the system works.

If you don't have the manuals you can click on the link below and download them:

http://www.bdub.net/factory-manuals.html

Regards,
Rob M.
The Pedantic Mechanic
USAussie - Downunder
USA '75 Avion - Double Trouble TZE365V100426
AUS '75 Avion - The Blue Streak TZE365V100428

-----Original Message-----
From: Lawrence Harrison

I have been working on my engine and jacked up the center front cross member for one day about 8 inches or so. After awhile upon
letting it down I noticed my rear suspension was lacking height. I have the batteries undone, have not run the engine for over a
month, and my grade in back is slightly sloped backwards compared to the front. When you look at the bellows they seem like they are
holding air and was wondering what I might have done. I have since jacked the back and supported the framing to keep the angle of
the bellows and pressure points more equal. Is it possible to close the valves before the bellows and pump compressed air into the
bellows to straighten them out? They have shutoff valves and then an air inlet valve just before the bellows. Are these air valves
used for pumping more air into the bellows if your system is down? Yes I am a bonafide rookie!!

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Regards, Rob M. (USAussie) The Pedantic Mechanic Sydney, Australia '75 Avion - AUS - The Blue Streak TZE365V100428 '75 Avion - USA - Double Trouble TZE365V100426

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Re: another potential problem! Why my air bellows are low? [message #227231 is a reply to message #227219]

Sun, 27 October 2013 15:18

Otterwan

Messages: 946
Registered: July 2013
Location: Lynnwood (north of Seattl...

Karma: 0

Senior Member

budworks521 wrote on Sun, 27 October 2013 11:46

Jacking up the front puts more weight on the back. Any leak you have would be exacerbated by the additional pressure and thus leak faster than usual. What might normally leak down in a month might leak down in just a couple days.

1977 Birchaven, Lynnwood WA - "We may not be able to stop all evil in the world, but I know that how we treat one another is entirely up to us."

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Re: [GMCnet] another potential problem! Why my air bellows are low? [message #227236 is a reply to message #227231]

Sun, 27 October 2013 15:49

emerystora

Messages: 4442
Registered: January 2004

Karma: 13

Senior Member

> budworks521 wrote on Sun, 27 October 2013 11:46
>> I have been working on my engine and jacked up the center front cross member for one day about 8 inches or so. After awhile upon letting it down I noticed my rear suspension was lacking height. I have the batteries undone, have not run the engine for over a month, and my grade in back is slightly sloped backwards compared to the front. When you look at the bellows they seem like they are holding air and was wondering what I might have done. I have since jacked the back and supported the framing to keep the angle of the bellows and pressure points more equal. Is it possible to close the valves before the bellows and pump compressed air into the bellows to straighten them out? They have shutoff valves and then an air inlet valve just before the bellows. Are these air valves used for pumping more air into the bellows if your system is down? Yes I am a bonafide rookie!!
>

You have level control valves by each airbag. It is controlled by the link to the arm. If you raised the front you probably moved the frame higher by the airbags which would cause the level control valve to dump air in an attempt to keep it level. Since you have not turned on the engine and the air pump it wouldn't be able to pump air back into the air bags so the rear of the motorhome would stay lower.

If you have the shutoff valves and the schrader valve stem you can open the shutoff valve to the bag and use an external air hose to put more air into them. Then you can close the air valves for storage. If you have to standard air bags they should be filled to about 90 psi.

Emery Stora
77 Kingsley
Frederick, CO
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Re: another potential problem! Why my air bellows are low? [message #227246 is a reply to message #227219]

Sun, 27 October 2013 16:25

budworks521

Messages: 137
Registered: October 2013
Location: Grand Rapids MI 1974 Pain...

Karma: 4

Senior Member

I am sorry, I must update my account info, I have a 1974 Painted Desert and it has the power level system. I have the manual and I am now convinced from your generous replies and reading that the system is low due to the battery being undone and coach not running for awhile. I have since jacked it up to normal height and blocked the supports until I finish rebuilding my upper half. Thanks

1974 Painted Desert 455 upper half rebuild constant project inexperienced mechanic Grand Rapids Mi Always trying to learn

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Re: another potential problem! Why my air bellows are low? [message #227262 is a reply to message #227246]

Sun, 27 October 2013 18:53

A Hamilto

Messages: 4508
Registered: April 2011

Karma: 39

Senior Member

budworks521 wrote on Sun, 27 October 2013 16:25

You need to keep an eye on the height of a '74. If it settles down all the way, it will break the wheel wells.

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Re: [GMCnet] another potential problem! Why my air bellows are low? [message #227264 is a reply to message #227262]

Sun, 27 October 2013 19:06

Mr ERFisher

Messages: 7117
Registered: August 2005

Karma: 2

Senior Member

I have since jacked it up to normal height and blocked the supports
until I finish rebuilding my upper half. Thanks

normally done with simple blocks under the bogie support when you park for
a while
link
http://www.gmcmhphotos.com/photos/jacking-up-the-gmc-hooks-ramps-n-stuff/p5273.html

gene

> You need to keep an eye on the height of a '74. If it settles down all
> the way, it will break the wheel wells.
> --
> '73 23' Sequoia For Sale
> '73 23' CanyonLands For Sale
> UA (Upper Alabama)
> CanyonLands most likely for a parts coach. Sequoia being restored to
> service.
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�Give a man a fish; you have fed him for today --- give him a URL and
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Re: another potential problem! Why my air bellows are low? [message #227267 is a reply to message #227219]

Sun, 27 October 2013 19:21

mike miller

Messages: 3576
Registered: February 2004
Location: Hillsboro, Oregon

Karma: 0

Senior Member

budworks521 wrote on Sun, 27 October 2013 11:46

... Is it possible to close the valves before the bellows and pump compressed air into the bellows to straighten them out? They have shutoff valves and then an air inlet valve just before the bellows. Are these air valves used for pumping more air into the bellows if your system is down? ...

Any cut off or Schrader valves in the wheel well are not stock but many (most?) coaches have them. Yes, closing them should be standard procedure during storage or most maintenance.

While I do not think it was your problem... The Power Level System doesn't need power to function... other than running the pump. (Kind of required to raise the coach.) So IF you left the system in travel and raised the coach, the system would have sensed the higher coach ride height and released some air pressure to lower the coach.

So... Why do I not think it was your problem?

Normally this comes from jacking the rear of the coach, and would let _ALL_ the air out of the system.

I suspect you just have some small air leaks.

Mike Miller -- Hillsboro, OR -- on the Black list
(#2)`78 23' Birchaven Rear Bath -- (#3)`77 23' Birchaven Side Bath
More Sidekicks than GMC's and a late model Malibu called 'Boo' http://m000035.blogspot.com

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