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Discussion Starter · #1 ·
im looking to get a 92-96 bronco, and i was wondering what problems the vehicle would have if it was fully topless, meaning the top over the bed removed, as well as the top over the cab and the pieces on the sides, with a 4 point roll bar installed? i heard the body would seriously flex like that.. is this true? and what do they mean?
 

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Well sure the roof provides some support from diagonal flexing, but with no stress relief (such as the bed/cab gap in trucks) the strain is transferred to the sheet metal of the Bronco body.

You'll soon (if not already) learn about the famous rain gutter cracks above the windows, which are a direct result of the body twisting as the frame flexes.

A proper rollcage has the side effect of decreasing the body flex, as well as increasing safety.

So naturally without the tops on the Bronco, there is less resistance to frame flexing (even if it was just the sheet metal), and it will definitely flex more.

It all depends on what you deem more important. No roof, or lack of increased flexing.
 

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Discussion Starter · #3 ·
so exactly where does this stress come from? from the torque of the engine and subframes, or from where? if i knew the source of the flex, then i could address it, a 4 point roll bar could help, be safer, and improve the cosmetics, but id like to eliminate the flex if i can, and what exactly happens when it flexes? (also, i was thinking of making some door inserts out of an old set of doors to look like the inserts you can get on the early broncos)
 

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The stress comes from driving over bumps. The bigger the bump, the higher the stress. Yes, the engine torque causes some, too, but not as much as the suspension.

Without the roof, the windshield would probably blow over into your face at high speed: the A-pillars aren't designed to hold it up by themselves. It's like cutting out the floor & then wondering why the seats fall. You're removing a significant part of the body structure.
 

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I would like to see a picture of a Bronco that is COMPLETELY topless.
 

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If you cut out the top of the cab structure, you'll end up with bunch of floppy sheetmetal. The C-pillar (at the tailgate) is strong enough to keep the rear of the bed together, but the B-pillars tie together in the roof. The A-pillars would probably be ok with the doors closed, but if you remove the doors, expect what Steve83 said.

The body damaging flex comes from frame twist that is concentrated at the B-pillars. The rear body mount so far back, and unsupported, that the whole bed section tries to tear away from the cab right behind the doors. A full cage tied to the frame at least where the body mounts are will help eliminate the flex, especially if you put in diagonals in the roof, behind the cab, and from the cab to the rear mounts.
 

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Don't forget flexing when going around corners as well! (I've been reading my racing books :toothless ) As you corner, the body mounts will try to hold the body in one piece, but any area away from the body mounts will try to move toward the outside of the turn (centripital force, IIRC). At these points the truck body will try to fold like a taco. The only thing preventing this are those body mounts pushing and pulling on their little piece of metal.

Be thankful it's a body-on-frame design. If you were looking at the movement on a unibody design (like I am on my saab) it can be quite a headache! Right now I'm considering how much damage I'll do to the body and frame by taking the front sway bar off and letting only the rear sway bar control body roll (so every time I go around a corner the car tries to "wring" itself).
 

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Ubermich
Bronco bodies are VERY strong - not as strong as a unibody body :D, but they're strong enough to be lifted by 2 points. I've done it several times. :toothless They don't fold.

But the weight & wind load of the w/s on the A-pillars will break them quickly without a roof or door to hold them up. Note in TheVon's pics that the vent windows & door leading edges are still there. Also, that '78-79 body sheet metal is thicker than ours, so those A-pillars can take a little more stress. smf is suggesting deleting the doors or cutting them down to just inserts, which wouldn't brace the w/s at all.

BTW
Who cut his doors that way & posted pics - BigNorm?
 

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Discussion Starter · #11 ·
i did imagine the A-pillars would be the biggest problem, i thought about removing the interior pieces of the A pillars to weld a piece of round tube steel along the sheet metal and down to the frame, and then fit the interior sections of the a pillars to fit over the tube steel so that it could full support the windshield, and not be noticable either, and should work like a roll bar on the front too.. and you all agree where the bed and cab meet is where the flex is the worst, would there be able way ot strengthen that? possibly by welding in some sort of supports between the quarters and the interior bed?
 

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spiel_mit_feuer said:
...weld a piece of round tube steel...so that it could full support the windshield...should work like a roll bar on the front too..
Not a chance! :twak That's like reinforcing a bumper with a band-aid.
spiel_mit_feuer said:
...where the bed and cab meet is where the flex is the worst...?
No, after you cut the roof out, that'll be rigid as hell. Then it'll flex at the bases of the B-pillars, at the backs of the threshholds.
spiel_mit_feuer said:
...by welding in some sort of supports between the quarters and the interior bed?
The body is GONNA flex. If you weld in a couple of braces, it'll eventually tear them away. The original body was engineered using a VERY complex technique called "Finite Element Analysis" so it could withstand its own flexing (reasonably well). Since you don't have the facilities to re-engineer your new roofless design, just LET IT FLEX. :shrug Build your door inserts to allow for it & maybe run a reinforcement up from them to the tops of the A-pillars, like the vent window frame does in the pics above.
 

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Discussion Starter · #14 ·
heres another idea.. build a roll bar up along the A pillars and along the top of the windshield, leaving the B pillar arch thing there, build a roll bar underneath it, and connect the two in the center, and perhaps convert the roof into a T-top setup, so you have the tube steel roll cage around the cab itself, concealed by the body pieces left, that way i can put the tops back on and still be able to put the entire vehicle back together for winter driving...im not sure i would ever put the hard top back on over the cab, i would like to get a half cab for it, ive heard of cutting off the back of the cab of the F-150, shaping it to fit with weather stripping and some kind of latches to hold it in place, and use it like a pickup truck during the winter.. the only issue i have with this is if i were to put a roll bar inside the B pillar section i would like it to be a 4 point bolted just inside the tail gate as well... my only issue with that would be how to get a cab back to fit with the roll bars... i COULD have the 2 back pieces of the roll bar able to bolt on and off, with a seperate set to bolt to the back of the cab, and then just inside the tail gate, so that it could further support the cab back piece.. does this make any sense?, so the 2 pieces that bolt inside the tail gate can be removed and a new set bolted in depending whether i go with the half cab or completely open it up
 
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