pivoting frames and mounting campers

[IdaSHO]

disagree.... captured spring mounts keep it much lower... but do agree with you that Idahsho's set up is one of the most compressed 3pt pivots I've seen. confused though.... IdahSho.... your pivot at the rear appears to sit a good bit lower than the fixed points at the front... maybe that does not matter since it is only pivot spot...??

Am I correct that your rear set up pivots under the chassis instead of above like most??

How does the habitat attach to the rear pivot framework?

That's correct. Since I have a 3-point setup, as apposed to a 4-point, the front and rear pivots do not need to be at the same elevation.

Overall height wasn't so much a concern, as a constraint. under full compression and flex, the rear tires, plus some room for snow chains, dictated just how low I could go.

As shown below, there is a subframe that bolts to the chassis, then a bed that is stacked on top of that.
The elevations at the bottom of the bed skins (yet to be done) is the elevation I needed to maintain for tire clearance.

Hard to see, but the bottom of the subframe actually sits below the top of the chassis, where the chassis is formed up and over the rear axle.
Working with the constraints I had, the subframe is less simple than Id otherwise like, but it works, and clears the frame and the rear leaf shackle hanger.
The result is a bit of a complicated subframe.

All in, it should look something like this... Just ignore the subframe shape and pivot locations....
The rendering shows the pivots, subframe, and stacked bed frame.

And finally, the proposed mounting method is as shown below.
The frame rails will be modified to accept mounting hardware that will be bolted to the camper.
Done right, this will simplify loading and unloading tremendously, as currently alignment is always a bit fun.
The current setup is also little more than bolts through the frame of the camper to the bed rails, that provide a moisture path into the frame of the camper.
This setup should self-align to a degree, and will allow the camper to be 100% sealed up as the mounts will be permanent.

 

[javajoe79]

Just to add to this discussion, here are some pics of my truck flexed out. I measured diagonally from points on the cab to the back corners of the frame, while flat and while flexed. I had very minimal change of around 1/2" in either direction. One picture show the separation between the subframe and frame at the spring mount. Of course this is unloaded so things could change once it has more weight on it but I can already tell that I want to open up the hole through the spring mount because it appears to be binding and I want to try softer springs in the mounts as well. My rear subframe will be similar to the front subframe but rigid in back with springs mounts in the middle of the chassis right behind the current spring mounts on the front subframe. Also my camper box will be mounted to the subframe with 8 polyurethane body mounts from Energy.

 

[Fatboyz]

I'm hoping someone in the know will see this. This is a long thread and may not get the attention a new post does. I'm spring mounting the front of my box(check out my build under my name if you want) and hard mounting the rear. I'm wondering where to source springs for the front mounts (Canada). How strong, etc. I'm only planning for a couple inches movement. As a note the most recent pics in my build show the overhang on the cab fairly close. I'm taking it back to my upfitter to do some more mods to my box and when we remount it, it will come up another inch at least.

 

[Chorky]

I'm hoping someone in the know will see this. This is a long thread and may not get the attention a new post does. I'm spring mounting the front of my box(check out my build under my name if you want) and hard mounting the rear. I'm wondering where to source springs for the front mounts (Canada). How strong, etc. I'm only planning for a couple inches movement. As a note the most recent pics in my build show the overhang on the cab fairly close. I'm taking it back to my upfitter to do some more mods to my box and when we remount it, it will come up another inch at least.

I have been wondering the same thing. I hear of people who have mounted via springs, and plan to do similar to keep weights and fabwork lower compared to a 3 point, but the specifics on springs and bolts to use seems to be unobtainable information.

 

[IdaSHO]

That's because there is no one-size-fits-all for spring mounted.
There are variables, that are application specific.
With a spring mounted setup, you are relying upon the box/bed to be strong enough to resist twisting, while relying upon the springs to be just light enough to compress.
Distance the springs much compress comes into play as well.

I'm sure somebody might be able to work up a model that could calculate the forces, thereby providing you with spring details, but most will rely on trial and error.

With 3-point (or 4) the bed literally floats on its unique plane, regardless of twisting force applied by the flexing chassis.
Properly done, there is little to no forces applied to the box/bed.

With the setup I'm currently working on, I did add rear mounted shocks to dampen the movement.
So the forces applied to the box/bed is limited to compressing/decompressing the shocks, and whatever small friction the pins see in the pivot bushings.

 

[Fatboyz]

Guess I'll see if I can find a spring manufacturing company and see if they have any suggestions.

 

[javajoe79]

I got mine from mcmaster carr. They’re die springs and come in nearly infinite rates and lengths. I guessed at a rate and will go by trial and error until I’m satisfied. They’re also pretty cheap

 

[Coachgeo]

I got mine from mcmaster carr. They’re die springs and come in nearly infinite rates and lengths. I guessed at a rate and will go by trial and error until I’m satisfied. They’re also pretty cheap

someone once mentioned "Gold" spring rate from McMaster Carr...... but I never could find such an animal there. Your mention of "Die Springs" let me about right to them.. sweeet. (see "color coded die springs link".. on this McMaster Carr page )

 

[Coachgeo]

but otherwise... yes there is a manufactured mount system for liquid haulage tanks that mount to trucks in same manner (captured spring front..... solid rear). I've linked it in here somewhere..... more than once actually.

 

[Chorky]

Here are some better shots of the business end of the pivoting frame...

Any plans for the body as well? I would imagine the cab is going to have just as much pressure on it from chassis flex as the factory rear bed. With a pivot flatbed, I would imagine this places even more stress on the cab from preventing the chassis from flexing. For myself I had considered removing the bottom (under mount) bushing and replacing it with a spring to give more give than the worn out bushing. I'm really not sure of the negative implications of this though....

That's because there is no one-size-fits-all for spring mounted.
There are variables, that are application specific......
With 3-point (or 4) the bed literally floats on its unique plane, regardless of twisting force applied by the flexing chassis.
Properly done, there is little to no forces applied to the box/bed.

Very true. The major thing I don't like about the 3 point mounts in this thread are the complexity and extra weight/height. I'm sure to not be alone in that the amount of added time/cost/engineering/physical height and weight added from a 3 point mount would make a project take too many years to accomplish to be reasonable at the cost of those years not out exploring. Unless one could find someone or a place to build it for you - but even local commercial and custom bed shops start to sweat the moment I suggest 'true off road' or 'frame flex'. So maybe a spring mount is a compromise, in that hoping a flatbed with boxes would be stiff enough, combined with an aluminum camper or shell would do the job without failure at the cost of a more advanced system? That is the hope anyway - I'm sure there are others in the same boat as myself in this....

but otherwise... yes there is a manufactured mount system for liquid haulage tanks that mount to trucks in same manner (captured spring front..... solid rear). I've linked it in here somewhere..... more than once actually.

Is this the link you mentioned? I just read all 32 pages, and it's the only link I saw that went to springs....
https://www.mcmaster.com/compression-and-die-springs

 

[Coachgeo]

.....Is this the link you mentioned? I just read all 32 pages, and it's the only link I saw that went to springs....
https://www.mcmaster.com/compression-and-die-springs

no

http://www.watertrucks.com/prod_cat.asp
http://www.tandbwatertrucks.com/store/p17/Water_Tank_Hold_Down_Spring_w/_Hardware.html

 

[javajoe79]

For reference I used
OD ID wire dia compressed length max load rate free length part#
1.938" 1.314" 0.312"____ 5.23" 597lbs 215lb/in 8" 196485K386

 

[IdaSHO]

Any plans for the body as well? I would imagine the cab is going to have just as much pressure on it from chassis flex as the factory rear bed. With a pivot flatbed, I would imagine this places even more stress on the cab from preventing the chassis from flexing.

Eh? Not sure I follow. The reason you use a torsion free setup is two-fold. It allows the bed/box to remain relatively unstressed, but it also allows the chassis to flex as it needs to.
I'm not looking to limit chassis flex at all, at all. Its an open-C channel frame, that is "designed" to flex. The cab wont see much stress, and no more than stock, as the chassis below the cab is nearly all boxed.
That, and the cab isn't 100% rigid. They flex a bit.
[/QUOTE]

 

[Fatboyz]

no

http://www.watertrucks.com/prod_cat.asp
http://www.tandbwatertrucks.com/store/p17/Water_Tank_Hold_Down_Spring_w/_Hardware.html

Thanks for the link, Several water truck builders here in Alberta!

 

[Chorky]

Eh? Not sure I follow. The reason you use a torsion free setup is two-fold. It allows the bed/box to remain relatively unstressed, but it also allows the chassis to flex as it needs to.
I'm not looking to limit chassis flex at all, at all. Its an open-C channel frame, that is "designed" to flex. The cab wont see much stress, and no more than stock, as the chassis below the cab is nearly all boxed.
That, and the cab isn't 100% rigid. They flex a bit.

[/QUOTE]

I was probably half asleep writing the question. So knowing full well that a C-channel frame is like a wet noodle, If you left on the factory bed or hard mounted a flatbed, the bed (whatever kid it is) would in some way, even if miniscule, prevent such flex, right? Just through force. Like trying to bend a piece of cardboard vs. 2 pieces of cardboard. Slightly more resistance to twist with the bed on, vs the bed off. So adding a 3-point mount is similar to taking the bed off as it allows the chassis to flex much easier since there is no resistance at all from any sort of bed attachment.

If I got that bit correct then....

One would think that the chassis under the cab is just as flexy still being C-channel. However, that amount of flex is being prevented from the cab itself being hard mounted. So the amount of stress placed on the cab is the same as that placed on the factory bed. So one could imagine to the absolute extreme that if you flexed the chassis enough it would break all the windows of the cab - yes I realize unrealistic, just trying to explain what I picture in my head. More realistically would probably be flexing stress being placed on the welds of the cab body weakening them over time and possibly causing cracking.

So, now you have a super flexy rear end, with the 3-point, and a not so flexy front end due to the cab hard mounted. So what about the thought of replacing the rear two (or 4) mounts of the cab, with springs, to allow for slightly more give than the normal hard mount and bushings? This in theory would allow the chassis to continue to flex slightly more than with the cab hard mounted, and not transmit so much stress from twisting to the cab, considering the rear end is allowed to twist easier than before.

Still half asleep - but I do hope this makes more sense... By the way, your work looks awesome! Wish I could find someone near by to help with my own rig since welding and fabrication is not really an option right now.