rvupgradestore.com Composet Products Fridge Defend
RV Life Magazine RV Park Reviews RV Trip Wizard

Author Topic: How Important are Balanced Air Bags  (Read 2342 times)


  • ---
  • Posts: 40
How Important are Balanced Air Bags
« on: December 08, 2014, 04:59:54 PM »
Our 1998 Newmar 40' DP has air bags.  When the coach is on level ground, and the engine is turned on for a while, the front driver's side inflates to provide 24-inches between the center of the wheel directly up to the bottom of the wheel-well; whereas the passenger's side only raises up to provide a clearance of 21-inches.  Thus a difference of 3-inches, which is enough to notice a difference between the two sides when viewing the coach from the front.  Both sides are at 16 inches with the engine off and the air purged.  Is this normal?  Does this create any safety issues?  How to resolve? 
2002 43' Newmar MADP w/tag-axle
500 ISM Cummins
2006 CRV Tow Car


  • ---
  • Posts: 86
Re: How Important are Balanced Air Bags
« Reply #1 on: December 08, 2014, 05:53:02 PM »
Several issues with what you have said.

The air bags should be plumed together so the air pressure is the same in both bags.  You might check to make sure because in some cases each wheel position has a control valve..

What you have not said is what is the weight on that wheel position compared to the other end of the axle.  If the load is not correctly distributed left and right that will place more load on one wheel position.  So lets say that you have 100 psi in each bag and the foot print of the air chamber in the bag is 10 square inches  then the math says that each bag will support 1000 lbs. (unit area pressure).  But what if one position is supporting say 1500 lbs. while the other end is 1000, it will do that by increasing either the psi or the area of the foot print for the heaver side.  Which simply says that one position will be lower than the other which could account for your problem.

Suggest you weigh the coach on a scale that will give you individual wheel positions weights.  They are not easy to find.  Many scales have curbs that keep you from doing what you need to do.  If you can find a scale and only place one side at a time on each pad you can get the weights that way.  But it will require a scale with at least two pads and sufficient room to have one side of the coach off the pads.  Do both sides paying attention to which wheel is being weighed in each weight.

If the weights are equal you then need to se if it has individual ride height control valves for each wheel position.  If it does have those valves you will need to check the source pressure at each bag to see is they are equal.  Then if they are equal the adjustment for the valve needs to be checked.  Replace the valve if every thing has checked ok.
Lenexa, KS
2006 GMC 3500 SRW D/A
2000 HitcHiker 31.5 BWTG

driftless shifter

  • ---
  • Posts: 2407
  • A Luddite with a stupid phone
Re: How Important are Balanced Air Bags
« Reply #2 on: December 08, 2014, 06:18:12 PM »
I think the bags in question are air suspension which are a different setup from helper type airbags. There are ride height valves of some sort. One of the guys that know a lot more will be along shortly I'm sure.

Bill & Nan
93 bounder 34, chevy chassis
couple of aircooled vw's, 1 fast(sold), 1 reliable(sold).  Dubless : (
USN '76-'80, 1 boat, USS Blandy, DD 943.
I'm an analog guy in a digital age.


  • Guest
Re: How Important are Balanced Air Bags
« Reply #3 on: December 08, 2014, 07:51:38 PM »
If it's not level something is out of whack. (that's a technical term......) MH airbag suspension is designed to keep things level. If one wheel is parked in a pothole the system should increase the pressure as needed to level things out. IMHO measuring to the body isn't accurate because you'll never find a parking lot that is perfectly level. My standard would be, is my floor (or counter, or whatever) inside level?

As you know there is parking level and then there is ride height. I think I hear you say that at parking level everything is level but at ride height it's not. It may be that a level rod has become disconnected and is inflating the bag to max when in road mode. Someone needs to go underneath in a safe manner to check the fill valves, the rods and ride height. Each coach builder has specs and a specific place to measure the ride height. Once you have those numbers you can identify where the problem is.



  • ---
  • Posts: 2027
Re: How Important are Balanced Air Bags
« Reply #4 on: December 08, 2014, 11:44:54 PM »
I'm not familiar with your suspension on a 1998 so I  would suggest you call the mfr of your chassis and have them email your schematic to you showing the air plumbing. This way you won't be guessing as to what you have and where. You can also discuss the specific ride height measurements of your chassis and where to adjust yours when you are on the phone with them. Once you know what you have according to your schematic it is easier to discuss any specific issues then.
Most have one or two control valves up front that control the inflation/deflation of the front suspension (bags) and it is similar for the rear. You check ride height similar to what you are doing but it's more accurate if you follow the specs in your manual regarding where to measure. You can also then find your ride height control valves and move the arms to see if you suspension is working properly. Then you can decide if you have a ride height problem or something else as suggested above.
Remember to protect yourself regarding clearance when working under the MH with air suspension. There is a lot of room when the bags are up, not so much when they deflate.
2009 Tiffin Allegro Bus 43 QRP
Powerglide Chassis, 425 Cummins, Allison 6 Speed
2010 CRV - Blackhawk 2 - Air Force One
2002 Heritage Classic
Washington State