Torsion-Free Sub-Frame

[SkiFreak]

It depends on how much chassis flex you want to cater for.
What type of vehicle is it going on? Is it a stepped chassis (like a Fuso) or a flat chassis? Are the 2 fixed points of the 3 point mount at the back or front of the chassis?

 

[pugslyyy]

http://www.rvnetwork.com/index.php?showtopic=98208 is a pretty good discussion, the pictures and attachments are all relevant to your question. Not knowing anything about what you are trying to do, I'm going to take a stab in the dark and say that 1" is probably not enough. I would probably go the spring/slide mount thingies.

 

[adam88]

It depends on how much chassis flex you want to cater for.
What type of vehicle is it going on? Is it a stepped chassis (like a Fuso) or a flat chassis? Are the 2 fixed points of the 3 point mount at the back or front of the chassis?

It's a 1 ton F350 truck chassis. It is flat all the way through, mostly, not stepped. The 2 fixed points will be at the front, with a 3 point mounted at the back. The truck will have stock suspension and normal tires, so it won't have too much flex.

http://www.rvnetwork.com/index.php?showtopic=98208 is a pretty good discussion, the pictures and attachments are all relevant to your question. Not knowing anything about what you are trying to do, I'm going to take a stab in the dark and say that 1" is probably not enough. I would probably go the spring/slide mount thingies.

Thank you for the great URL. So, if the 1" of space is not good enough, I have considered spring/slide mounts. I understand these can be attached with the frame directly on the frame. Would I need to install the spring mounts in all 4 corners, or just in the 2 rear ones. Do you know anywhere that sells spring mounts like this.

Thanks for both the replies.!

 

[adam88]

Hmmm. After looking through that thread (I've seen it before), I think I still want to go with a 3 point system. The spring mounts won't get me the amount of flex I want. So I guess the question is, what is the minimum amount of frame clearance I need (to keep the bed as low as possible), while still maintaining flex and avoiding the flatbed frame "bottoming out" on the truck frame. I am not sure how I would calculate this.

 

[pugslyyy]

Quick and dirty would be to cross-axle the truck and measure how much frame twist you get (raise the front driver side and rear passenger wheel until the other 2 wheels are just lifting off the ground)

 

[gait]

I allowed for 15 degrees of twist in the chassis,

dynamic loads and movement can be surprisingly much larger than static,

I had the benefit of a manufacturers rear wheel bounce diagram, the clearance from body to wheel is as important as chassis to sub-frame

 

[fluffyprinceton]

I had the benefit of a manufacturers rear wheel bounce diagram, the clearance from body to wheel is as important as chassis to sub-frame

Dig through the truck manufactures site for "Body Builders Manual" there will be data on rear wheel bounce which gives you the clearances from tire to bed on a static frame.

To gauge frame twist jack up one side of the rear axle till the front wheel leaves the ground - observe the twist...if there's an existing body you'll have to figure out how it changes the unladen twist amount - while if it just a cab & chassis you'll have to figure out how carrying a body & load will effect the twist. In short I don't know of any manufactures documented info on frame twist under different operating conditions (unimog is likely an exception) so you have to figure it out yourself or copy an existing solution.
It is a critical design point as you want the bed height as low as possible but not too low...and a bed in a single plane is much easier to build & adaptable to multiple uses.Moe

 

[Flys Lo]

fluffyprinceton gives some really good advice.

In addition, how old is your F350, are you still using the F350 cab?

Don't compare a Fuso/Isuzu chassis and mounting requirements with an F350 chassis. Depending on how rigid your body mountings for your camper are (and how many of them) you should be able to "hard mount" the camper to most F350 frames if you are still using the F350 cab on the frame. The chassis for an F350 is much more rigid than a Fuso/Isuzu, and its mounting points are distributed over a much shorter distance.

 

[riptilyaflip]

Man I'd sure like to see the pop-up book version of this discussion.

 

[haven]

Check out the writeup about Pugsleyyy's camper build. The section on figuring out how to mount the flatbed, with photos, is very helpful.
http://www.truckcampermagazine.com/off-road-expeditions/the-overland-fuso-truck-camper

 

[haven]

More information (36 pages worth of discussion) on "kinetic" subframes can be found here
http://www.expeditionportal.com/forum/threads/25494-pivoting-frames-and-mounting-campers

 

[pugslyyy]

Not mine but similar -- and yes some of the best info on how to do that particular mounting system that I've seen.

 

[haven]

Sorry for the confusion. Is there a build thread here for the Fuso shown in the article?

 

[pugslyyy]

Sorry for the confusion. Is there a build thread here for the Fuso shown in the article?

I seem to remember there being one but I haven't been able to find it.

 

[haven]

I think it's Buckstopper's project. The build thread is here
http://www.expeditionportal.com/forum/threads/105380-Buckstopper-s-FG-Build