Pivot Frame on Crew-Cab Pickup?

[Korben]

I'm new around here and before coming here have never been exposed to how you folks are using pivot frames. I roll a 89 F350 Crew-Cab Long-Box, as you might imagine frame flex is a BIG issue for me. So far I've broken a core support, windshield, and fiberglass canopy as the direct result of the body being forced to flex with the frame. Of course there's also all the annoyances of things like not being able to get the tailgate open. So I was reading IdaSHO's posts about his truck and his 3 point pivoting bed thinking heck I could apply this to my truck and even take it a step further. If you've read some of my other posts you might know that I have a lot on my plate. But I like to plan things out a lot in advance and well it's time better spent then watching TV, so I'd like your thoughts on what I have in mind.
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So here's my line of thinking, and to be clear this would be with a standard bed, not a flatbed or camper. Also I should do a body lift anyway, something in the 4" area I haven't really pinned that down yet. So anyway what I'm thinking is a double 3 point setup. One each for the two halves of the truck. One for the cab and front clip, and one for the bed. A secure stock like mounting at the back of the cab and front of the bed. Then a center pivot at the core support and back of the bed. I hope my words so far are enough to get across what I'm thinking.
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I really only foresee two issues, first how much pivot area do I need under the back of the bed to keep the frame from contacting the bed. Secondly for the front half I'm going from 8 mounts to 3, I'd have to find a way to reinforce the cab and the connection between the cab and core support, the fender alone isn't going to do it. As far as bed to frame space I'd expect the space created by 4" of body lift to be enough but I really don't have a good reference for that yet. For the front of the cab, fender, core support connection I can imagine making a framwork that connects at the front cab mounts, maybe ties into the fender somehow, and connects to the core support. Of course there's also all the unknown unknowns, thoughts?
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[pappawheely]

I've never heard of anyone doing the cab. Shift linkage, e-brake, wiring and the steering column will get interesting.

 

[Korben]

I've never heard of anyone doing the cab. Shift linkage, e-brake, wiring and the steering column will get interesting.

Put some thought into that stuff. Manual trans w/hydraulic clutch so shouldn't be an issue. Steering shaft has joints and won't be any worse then a tall body lift, but should replace the rag joint with a u-joint, the aftermarket supplies that. Hadn't thought about the E-brake cable, sucker is kinda short right there. The two worst I figure are the brake lines between the MC and frame, I'll want to replace those with flexible line. And the radiator to engine relationship, need an electric fan and to make sure the upper hose has enough flex.
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Like the general idea though, you know how much the front half of a crew cabs flexes with what you do with yours? It's harder to notice with the front but it flexes as much as the back, or would if the body wasn't preventing it, which of course is bad for the body. You can see it in this pic(not me)
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Or more so in amgvr4's video at between 5 and 6 min. When looking from the front your see the body to bumper gap, and that's with the body flexing a lot to match the frame. You see how much the body flexes a few seconds later when you have a side view, watch the fender to door gap.
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[Higbean]

Cool truck man.

I think I'd rather bust windshields, camper shells and core supports than take on a potential engineering nightmare like a pivot frame. You could always box the frame to add stiffness but I'd just keep running it as is and beef up the stuff that breaks until she holds together or needs to go to scrap.

 

[jeep-N-montero]

Cool truck man.

I think I'd rather bust windshields, camper shells and core supports than take on a potential engineering nightmare like a pivot frame. You could always box the frame to add stiffness but I'd just keep running it as is and beef up the stuff that breaks until she holds together or needs to go to scrap.

I agree with this suggestion.

 

[Seabass]

I got the same truck. Busted three years ago. Just keep driving!!!

 

[pappawheely]

I'm curious why Ford designed the frame so flexy to begin with? My windsheild is busted too.

 

[snowaddict91]

My windshield isn't cracked, because I just had to replace it to pass inspection, lol! But my core support is...someday I will deal with that.

 

[Korben]

Cool truck man.

I think I'd rather bust windshields, camper shells and core supports than take on a potential engineering nightmare like a pivot frame. You could always box the frame to add stiffness but I'd just keep running it as is and beef up the stuff that breaks until she holds together or needs to go to scrap.

Wow pity anyone that would buy a used vehicle from you. I originally saved this truck from going to scrap, I sure as heck ain't sending it there.
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I don't really see an engineering nightmare, certainly nothing much harder then a 4 link and body lift.
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Boxing the frame is in no way practical and that IS an engineering nightmare. Have you ever boxed a frame before?

 

[Korben]

I'm curious why Ford designed the frame so flexy to begin with? My windsheild is busted too.

I'm sure it's a better to bend vs. break thing, commercial trucks have very flexy frames as well. As long as they are and with all these tucks are put through you almost never hear of broken frames. When you do it's usually from a poorly conceived modification.
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EDIT a lot of rigs are designed to flex, from old Jeeps where the mount for the grill is one piece in the center, to many semi trucks where the cab is mounted a lot like what I have in mind. They often have 2 solid mounts in the front corners and two very soft mounts(often air bags) close together in the back center of the cab. The question really should be why didn't they design the body work to deal with it better.

 

[IdaSHO]

Its doable. And with a quad cab the cab flex is certainly a bit of an issue.


instead of a pivot frame, I think you should instead investigate a front hinge and rear bags.

Similar to how many big rig air-ride cabs are mounted.



Doing that would require the pivot to be as far forward as the core support.
So everything... grille to rearmost portion of the cab will have to be supported by a subframe.

 

[Korben]

Its doable. And with a quad cab the cab flex is certainly a bit of an issue.


instead of a pivot frame, I think you should instead investigate a front hinge and rear bags.

Similar to how many big rig air-ride cabs are mounted.



Doing that would require the pivot to be as far forward as the core support.
So everything... grille to rearmost portion of the cab will have to be supported by a subframe.

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I thought about that, and for many that might be a much better option. However it would make for even more of a misalignment between the cab and bed. I'd really like to be able to make modifications/additions like a full length roof rack and a canopy window seal that would otherwise be damaged by the bed and cab going far out of alignment. If I make the rear cab mounts the solid ones/hinge then that they are so close to the front bed mounts would minimize the two halves going out of alignment.
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Been thinking about the subframe, as luck would have it I have another frame. I could make it out of/based on that frame so that the contours and mounting is identical to the original frame and it largely is parallel to it.
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EDIT...
Hmmmm, thinking out loud, if I made a subframe like that out of another identical frame then if I made it just a bit longer I could include the front bed mount in that subframe completely eliminating any bed to cab misalignment. Heck it could go the full length of the truck, basically a pivoting stacked frame. It wouldn't be that simple I don't want THAT much body lift so I'd have to modify it a fair amount, shorter wider so that the vertical panel will fall outside the original frame rail. IIRC the only significant thing on the outside of the frame rail that would be hard to work around is the front shock mount.
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IdaSHO, how much space did you find you needed above the frame to allow it to twist without contacting anything?

 

[pappawheely]

Won't the subframe built from another frame flex the same as the original frame?

 

[Korben]

Damn, that GIF hypnotized me for a while, lol.
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And no, there would be no suspension or drivetrain stress on that frame.
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[pappawheely]

I just wanted to post that GIF. :wings: