Well, I broke it.

[pugslyyy]

I think that's up to the purchaser. Most fabricators sub that out anyways.

 

[pugslyyy]

I've been working on the solids for the new frame so that I'll be able to make sure everything will fit back together as planned. Haven't put the holes in yet, but I think I've got the constraints right. I can slide the crossmembers around inside the framerail, so the exact placement and length of the frame are still not nailed down.

 

[GR8ADV]

It's been frustrating to be missing the single most important piece of data - load weight - when discussing the frame strength and appropriate camper mounts on the FG...Moe

Clearly important in the discussion. But there is much more than that.
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In generalized terms the bending loads on a simply supported beam or frame rail with a uniform load increase by the square of the length. So if one were to increase the wheelbase for example by 20% then the bending stresses on that member increase by 44%. Thus the allowable load (the weight of your box) would need to decrease by 44% to not exceed the design loading stresses in the rail. Similar issues can apply with other modifications like extensions etc.

 

[pugslyyy]

I was wondering, from picts is saw,what if you reversed the three points? Meaning the single point up front and the two in the rear. The center of the frames seems to be where it would twist the most. Seems like would allow you subframe to twist with less resistance or tension.

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Yeah I could see how it might be better - not sure if it does more than postpone the inevitable though, you still have that point concentration of the load when you hit bumps, potholes, etc. I'm convinced that's the real killer.

 

[pugslyyy]

Well here comes out my thoughts...

Frame extended, too much weight too far back. Past what the frame was designed for. Frame breaks. Frame gets fixed with a heavier duty frame that no longer is designed to flex like original. Fixed? No. The lack of flex on the rear frame is now transferred to the frame that still flexes in front. Another break. Perhaps that frame was damaged months ago and the compounded stress has finally made it snap due to the transfer of forces.

Okay now what I would do...
Doug is brilliant. I have seen his build. Actually the systems he put into the truck and how they are organized reminds me of the space shuttle. I just can't believe that someone single handed could create something like this. But I think having that motorcycle garage perhaps wasn't a good idea. Could camper be positioned over the cab over. Perhaps perhaps not. Would that have created a high center of gravity to allow the cab over to rotate open which would have too much twisting force with the extreme weight and destroyed the frame anyhow? Doug must have been an engineer from what I have seen from the systems he created. You see, I think over the long term this repair you did perhaps is a temporary measure and something else will snap.
Okay NOW what I would do. I would either fix the frame up front and move that camper forward if possible or...
Take that space shuttle off the back of the truck and give up on the fuso. Sell it for what you can get out of it. Find a Ford f450/F550 7.2l truck and put that space shuttle on the back of it. Hmm like an Earthroamer.
We all feel bad this happened to you but you got this amazing truck for a steal broken frame or not. I wish the best for you in this and hopefully this info will help you in someway. I don't know. Put it on a Ford f450/f550. Or course, this all takes cash and time or lots of cash. I don't want to discredit Doug in all of this. He is simply brilliant and someone I highly admire and respect like the rest of us.

Heh, I'm not just a pickup truck guy.

From my perspective that's a lot of overthinking, followed by throwing the baby out with the bathwater.

Truck frames break on a regular basis, it's not a big deal. There are guys with welding trucks who travel from one job site to another putting stuff back together.

This frame has been through enough that it really isn't worth trying to sleeve or box in. The low quality, thin steel is just not worth trying to work with. As has been pointed out, I don't have the option of derating the chassis in fact the opposite would be desirable.

All of the breaks / bends / issues have been on unreinforced sections of the frame, and I'm very confident that moving to a thicker frame built from a high strength low alloy steel will mitigate the issue.

Even though I think the new frame would be okay with the existing 3 point, I'm going to abandon that in favor of the spring-mounts. So a belt-and-suspenders solution.

 

[pugslyyy]

Once you get the body off, it should look a lot easier than you think. The frame will be riveted up into the S-section. Use the back edge of the S-section as the reference point. Mark a line there on the old rail.....measure everything foreward and aft from that line.

...

Replace every rivet with 12mm high tensile bolts with nyloc nuts and a washer on both sides..... Or Huck rivets are nice if you can hire or borrow a gun.

...

Regards john.

Thanks John - I'm starting to think more seriously about the fasteners now. Since I'm in the US my plan is to use 1/2" grade 5 fine-pitch bolts torqued to 64 ft lbs. Does that sound about right to you?

Also, since it is new rails and crossmembers just replicate the hole patterns / number of holes or do anything different?

Appreciate the advice, it's been very useful!

 

[SkiFreak]

As you would obviously know, the OEM chassis has many holes in the chassis that are not used. Given that you know exactly what is going back onto your truck, replicating all of the OEM holes seems a little pointless.

 

[JRhetts]

You guys would certainly know better than I, but might any of the holes be for stress relief or to calibrate stiffness under torsion?

 

[Overland Hadley]

You guys would certainly know better than I, but might any of the holes be for stress relief or to calibrate stiffness under torsion?

I have wondered the same thing about all the unused holes in a truck frame.

 

[Overland Hadley]

You definitely have my respect. I doubt I would have had the courage to share all the details in a public forum.

Yes. Thank you for sharing this process.

 

[pugslyyy]

As you would obviously know, the OEM chassis has many holes in the chassis that are not used. Given that you know exactly what is going back onto your truck, replicating all of the OEM holes seems a little pointless.

Yeah, I meant replicating the bolt pattern between the crossmembers and frame rails. I don't plan on making any more holes than I need to!

 

[GR8ADV]

You guys would certainly know better than I, but might any of the holes be for stress relief or to calibrate stiffness under torsion?

Yeowza. I am not aware of any situation where drilling a hole in a beam makes it stronger in any way. But hey I have been wrong before.
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This thread increases my awareness that there are people who think that the structural members size (thickness, thinness, height, weight etc) , shape (channel, box, tubes or I-beam), connection points and methods of connection etc are all picked by some random guy with a welding torch. These things are very well engineered with load limits and load placement parameters. (they actually went to school for this. just sayin.) :elkgrin:
.
Holes in a member are usually there for two reasons. 1) to make an item lighter. 2) to provide for mounting locations, or pass through locations etc. In either case the holes are accounted for in the strength of the member. Typically holes are 'allowed' if by including them the ultimate design strength of the member is not compromised (under the load parameters) . They are accounted for in the analysis of the member.

 

[mog]

This thread increases my awareness that there are people who think that the structural members size (thickness, thinness, height, weight etc) , shape (channel, box, tubes or I-beam), connection points and methods of connection etc are all picked by some random guy with a welding torch. These things are very well engineered with load limits and load placement parameters. (they actually went to school for this. just sayin.) :elkgrin:

Amen to that !
The poor Fuso gets a much-maligned frame here on the Expo Portal.
In my research all the tens of thousands of commercial Fusos on the road seem to have no issues with sub-par frames unless they have been abused (snow plows) or rusted (snow plows, hauling corrosive materials & rust belt trucks).
Are they as strong as a comparable Iveco (1st hand knowledge), or an Isuzu (specs), IMO no. BUT are they as strong as they need to be for their designed parameters, IMO yes.
Are they a Mercedes Unimog or 1017 designed with a 3 or 4 point subframe in mine, no.
Once you start operating anything outside it's designed parameters, then the item is not at fault, it is the new designer/operator.
I've had my Fuso at 20%+ over GVW with no problems. Did I do that off-road, no. Did I do that long term, no. Would I make that a routine operation, no. Did I take extra precautions operating over the GVW, yes. So the burden of something going wrong was on me, not Mitsubishi.

 

[pugslyyy]

Yeowza. I am not aware of any situation where drilling a hole in a beam makes it stronger in any way. But hey I have been wrong before.
.
This thread increases my awareness that there are people who think that the structural members size (thickness, thinness, height, weight etc) , shape (channel, box, tubes or I-beam), connection points and methods of connection etc are all picked by some random guy with a welding torch. These things are very well engineered with load limits and load placement parameters. (they actually went to school for this. just sayin.) :elkgrin:
.
Holes in a member are usually there for two reasons. 1) to make an item lighter. 2) to provide for mounting locations, or pass through locations etc. In either case the holes are accounted for in the strength of the member. Typically holes are 'allowed' if by including them the ultimate design strength of the member is not compromised (under the load parameters) . They are accounted for in the analysis of the member.

It's not an issue of the product being designed by a knucklehead, it's that every design is a compromise between many competing objectives. How strong do you want it to be? How heavy do you want it to be? How expensive do you want it to be? You optimize the model by chosing "as strong as it needs to be", "as light as possible", and "as cheap as possible"

Mitsubishi is pretty upfront about the FG not being an offroad vehicle (despite how we use it), with detailed specifications on how to mount bodies (which most 3 point approaches that I've seen ignore).

There's a saying that I've always liked - "Anyone can build a bridge that's strong enough - but it takes an engineer to build a bridge that's JUST strong enough"

 

[GR8ADV]

- "Anyone can build a bridge that's strong enough - but it takes an engineer to build a bridge that's JUST strong enough"

Yes and history (ancient and modern) has shown us that in order for that 'anyone' to build it strong enough they first had to build one or two that collapsed.
.

Oh yes, and as always: Light, Strong, Inexpensive. Pick any two you want.