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I added a pair of overload airbags on the rear of my truck. In so doing I had the rear end jacked up by the frame with all weight off the rear wheels. Since then the truck rides like I have no shock absorbers at all regardless of whether or not I have air in the bags. When I'm on rough or uneven road it's continually bouncing. A pothole hit produces a jarring thud. Is it possible that taking the weight completely off the suspension like that somehow damaged my shocks?
I've seen it happen but when it happened to me I had let a car down off the lift and one shock stuck in the fully extended position. I had to bounce it through a couple of potholes to get it to relax. Jump up and down on the bumper on one side and then the other, you probably just have one bad.
Gary, How do the shocks seem to work if the air bags are at their minimum recommended inflation pressure? You have a mechanical system with essentially three elements: viscous velocity dependent damping (shocks), mass of the vehicle riding on shocks, and the combined spring coeficient of the springs and air bags added together. I have custom spring packs on the rear of my Dodge-Cummins 1 ton in place of the original springs, custom overload packs in place of the factory overloads, and 10,000 lb rated air bags to give me some additional but adjustable support. I am runing Bilstein gas charged shocks (highly recommend them to you, Ranchos as second choice) Dual shocks in front and singles in rear (couldn't find a place to add duals in rear.)
If I inflate the bags to (or near) upper rating (100 PSI) the rear end gets real stiff and bouncy, too much spring constant for the mass and damping. Gotta stop on and gently drive down a speed bump to avoid back pain/injury. If I put the camper (largest slide in camper Lance made in '97) in the utility bed thus increasing the mass a bunch the rig rides like a dream with any air bag pressure within ratings (5-100 PSI).
Not saying your shocks aren't insufficient but you might be running too much air pressure for your load.
Lecture folows (migt be on mid term):
There are three possible combinations of mass, damping, and spring constant. Underdamped, critically damped, and over damped. An underdamped system (worn out shocks) is illustrated by noting that when the vehicle is bounced up and down and then observed it goes up and down more than 1 1/2 cycles (maybe several) as the oscilation decays to a stop. With an over damped system (too much shock absorber action) when the vehicle is bounced and released it returns to its neutral position without passing neutral and returning. The critically damped system (vehicle) when bounced and released will pass through its neutral (rest) position ONE TIME and then return to the rest position.
Often times in various situations involving damped mechanical systems, critical damping is desired. It isn't toooooo stiff and it isn't toooo bouncy.
Pat (I wasn't kidding about the mid term exam)
Pat,
That was one heckuva good explanation. Amazingly though, I think I actually solved the problem before I read it. [img]/forums/images/icons/shocked.gif[/img]
It turns out that if you're frugal and modified and fabricated your brackets from the Z-71 extended cab to install your air bags under a Tahoe and that increased the bracket height under the frame by about three inches then you have effectively shortened the travel for your springs and shocks by about three inches. With no air in the bags the shocks are extended out that much further. Now if you factor in that your springs aren't able to compress as far before you end their travel rather abruptly because you've taken that same three inches from their travel.
All of that would probably still be fine if you keep an appropriate amount of air in your air bags. If you happen to do all of that and then don't fill your air bags, you'll have ride problems because of the oversized bracket beneath the frame.
That also happens even if you do fill your bags to the point of raising your rear bumper as much as five or six inches if, in your bag installation process you didn't get one connection quite square and true allowing all of the air you added to leak out in about the time it takes you to put away your air hose, turn off your compressor and lights, lock your building, get in your Tahoe and start to drive away. [img]/forums/images/icons/blush.gif[/img]
It's amazing how much nicer that Tahoe rode tonight without the air leak so I actually do have air in my air bags. [img]/forums/images/icons/wink.gif[/img] [img]/forums/images/icons/smile.gif[/img] [img]/forums/images/icons/grin.gif[/img]
I think I am going to consider contacting the bag manufacturer to see if they'd sell just the connecting brackets for those bags and a Tahoe. Your suggestion for new shocks is probably a good one, too. The pair that are on there are pushing three years old at least (and that's if they were new the day before I bought the Tahoe). [img]/forums/images/icons/grin.gif[/img]
Gary, I got only 10,000 milles on OEM shocks, switched to Bilstein gas charged (double in front single in rear) and at 68,000 (58,000 on Bilsteins) shocks are still doing great with no discernable degradation. If you run your air bags at zero psi you can pinch and ruin them.
I have mine plumbed separately so I can adjust tilt left to right as well as adjust rear ride height. I have a dual gauge (one scale two needles) to give cockpit indication of the pressure. I have valves to add air or release air from cockpit and a 12 volt compressor to supply the air for bags. It has extra outlet for airing tires or whatever. Someday I hope to add air horns off this air source. I had them on prevous rig and used to give a "safety toot" before rounding blind curves in the mountains. It made a big difference in the number of motorcycles and sports cars that would come around the corner half way in my lane. Something about a "Big Rig air horn" that tends to encourage folks to stay on their side of the double yellow lines.
Parting comment: Please remember that the air bags do not increase your carrying capacity they just let you carry the load level and without stressing your springs so much.
Pat
I noticed tonight that I've still lost some air so I must not have completely sealed the connection that was bad or may have a problem elsewhere. I've still got air pressure but it's noticeably down. I think that'll be a probem to check tomorrow. I want to get the chance to play with this system a bit before I commit to an on board compressor, etc., but I do like the idea of having one if I can get comfortable with the air bag system.