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Old 04-23-2012, 07:08 PM   #1
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Default Air Bags

To recap, I'm planning on getting a semi, removing the sleeper, putting a box on the back and pulling a trailer..... sort of like this:



I'm thinking about putting the box on the back of the truck on air. Bags are relatively cheap. I do need a way to keep the box located. Plates with slots? Panhard rods? And, ride height.

Does anyone have a good primer on air ride height control? Trying to figure out how to do that properly..... Also, can you put full weight on a deflated bag? Or do I need to have stops so the bags are not fully compressed when the system is not charged...?

Thanks.
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Old 04-23-2012, 09:46 PM   #2
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I would think you'd put stops on either side of the bag. Steel, maybe hardwood.

It sure looks purdy.
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Old 04-23-2012, 11:12 PM   #3
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I would think that hard rubber stops/mounts similar to what you would find on a leaf spring suspension to prevent bottoming out would be your best bet. You do not want the empty air bag to support the box weight. (air bags do not like to be over extended either) You will defiantly want some way to limit any side to side movement. Not thinking a plate with slots is going to work very efficiently. There will be a lot of motion going down the road, and you will need some type of bearing surface to prevent wear on the plates, and or lots of noise coming from steel on steel. some type of links with bushings or heim joints may work. Take a look at how some of the trucks are mounting their sleepers, especially the unitary cab/sleepers. Most of them are supported by air bags. Some of the older rigs had a hinge point for the cab way up front and the rear of the cab and sleeper was on bags, this gave a better ride but still had some side to side stability due to the hinges. Not very practical for a long box though. Also consider adding some shocks to the set up, an air bag is basically an adjustable spring, and will bounce like crazy without a shock to dampen it. The amount of air in the bag can be controlled with a ride height valve similar to what is on the rear suspension of an air ride truck, a lever is moved up and down as load is increased or decreased and the valve its connected to will regulate pressure in the bag to keep ride height the same. This can also be done manually with a regulator which can be adjusted up or down as needed depending on weight. This can work well if weight is not constantly changing. , and with an RV box might be simpler than an automatic system, unless you can pirate one from a junk yard truck suspension.

I have been contemplating some type of air bag setup for the conversion I am planning. As of now, I am still leaning toward the tried and true hard mount to frame rails. I am concerned with coordinating movement between cab and box, especially if both are on air. Not sure I would want to bolt/weld/Velcro the cab and box together into one long unit either, so much twist and torque going through the frame when going up driveways etc.

Keep us posted with what you end up figuring out. Always looking for a better mousetrap.

Good Luck

Dave
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Old 04-24-2012, 01:07 PM   #4
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With the plates I was thinking of a layer of UHMW or Teflon in between the steel. Very slippery. Yes, I agree the box and cap need not be rigidly attached to each other. The accordion seal is what I'm thinking right now. I am hoping to reuse whatever is there when I pull the sleeper off. My thinking is that both the cab and the box should be bouncing in the same direction. Yes, shocks for dampening did come to mind.....
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Old 04-25-2012, 09:19 PM   #5
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Quote:
Originally Posted by Oscarvan View Post
layer of UHMW
What is UHMW?
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Old 04-25-2012, 09:21 PM   #6
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Consider putting in a Watts Like, just like they use on race cars. The travel will be limited. Should be easy to do that will allow the box to move up and down with easy. Put one in front and one in back. Should be easy to fab up with big Heim joints and heavy steel tubing.

Watt's linkage - Wikipedia, the free encyclopedia
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Started looking for 379 Peterbilt TC, 24' to 30' box, bumper pull--but ended up w/1999 Liberty Coach conversion of 45' Prevost XLV bus. 1,000sf heated/AC'd race shop w/dump station, 50amp shore pwr where bus parks, 3 NASCAR/ARCA race cars & 26' Bravo trailer.
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Old 04-25-2012, 11:59 PM   #7
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Ultra High Molecular Weight, its a dense self lubricating plastic, very slick and tough. makes a great bearing surface, and comes in all kinks of thicknesses.
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Old 04-29-2012, 11:05 AM   #8
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I really don't think that you will like the box moving around on the truck. Probably best to get a truck with air ride suspension and mount the box solid to the frame.
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Old 04-29-2012, 06:35 PM   #9
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Quote:
Originally Posted by #90-GTSC View Post
Consider putting in a Watts Like, just like they use on race cars. The travel will be limited. Should be easy to do that will allow the box to move up and down with easy. Put one in front and one in back. Should be easy to fab up with big Heim joints and heavy steel tubing.

Watt's linkage - Wikipedia, the free encyclopedia
A simple panhard bar might work too. All depends on how much up and down travel you want for the box.
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Started looking for 379 Peterbilt TC, 24' to 30' box, bumper pull--but ended up w/1999 Liberty Coach conversion of 45' Prevost XLV bus. 1,000sf heated/AC'd race shop w/dump station, 50amp shore pwr where bus parks, 3 NASCAR/ARCA race cars & 26' Bravo trailer.
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Old 04-29-2012, 07:39 PM   #10
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i think a guy put his box on cab air ride bags. travel was limited to about 3". he just made steel plates to mount. i think he had 4 or 5 per side.
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