Roll cage questions concerning body cracking - Ford Bronco Forum
 
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post #1 of 16 (permalink) Old 05-24-2016, 01:34 PM Thread Starter
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Roll cage questions concerning body cracking

I am confused about whether or not the body should be tied to the cage or allowed to float free of cage.

I have seen cages that were tied to the floor with plates from there to the frame by the use of outriggers. They were also tied into the A and B pillars with plates. Also seen tubes added to that pass thru the plates into the tube ID to prevent shearing.

I have also seen where the cage was build so that any down bars past thru holes in the body to the frame and not tied to the body at any point. The reason told was that it allowed the body to float and would prevent body seams from cracking.

Which is proper and why? Many ways to skin a cat, but only a few are correct. Some of which it appears may cause body seam cracking.

Found a back hoop design that I like but needs modifications to strengthen side crush. It will allow fairly easy access to the rear seat area and still provide back of front seat protection.

It needs X bars below the belt horizontals and needs a tube under the floor from frame rail to frame rail to support the center legs. If done correctly it should line up with the frame outriggers supporting the hoop down tubes.
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post #2 of 16 (permalink) Old 05-24-2016, 01:46 PM
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this is interesting. i have a cage mounted to the body, but would like to eventually tie it to the frame...

i spoke to a few shops and they said they could do a tie from under the body to the frame. they didn't mention cutting through the body.

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post #3 of 16 (permalink) Old 05-24-2016, 02:04 PM
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Looks like Iain Harrison's Bronco that they did on Dirt Every Day, but with an updated cage design.

Rear seat access is one of my concerns about putting a cage in mine. That looks like a nice solution but It would still make my rear seat passengers climb over the center console. Wonder if it interferes with the back seat folding forward.

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post #4 of 16 (permalink) Old 05-24-2016, 02:43 PM Thread Starter
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Originally Posted by RAMPNT1 View Post
Looks like Iain Harrison's Bronco that they did on Dirt Every Day, but with an updated cage design.

Rear seat access is one of my concerns about putting a cage in mine. That looks like a nice solution but It would still make my rear seat passengers climb over the center console. Wonder if it interferes with the back seat folding forward.
Very good memory it is Iain's. I figure stepping over a corner of the console is better than trying to squeeze thru X bars.

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post #5 of 16 (permalink) Old 05-24-2016, 02:52 PM Thread Starter
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Originally Posted by dash_cam View Post
this is interesting. i have a cage mounted to the body, but would like to eventually tie it to the frame...

i spoke to a few shops and they said they could do a tie from under the body to the frame. they didn't mention cutting through the body.
Depends on how they do it. Each downtube will have a plate welded on the end of it. Under the floor the outrigger will have a matching plate welded on it that will bolt thru the floor to the top plate. Only holes in floor are for the bolts.

The other way is similar except they will cut a hole the size of the tube ID thru the plates and floor. Then a tube or I have even seen solid bar is slid inside the downtube and welded. Then this piece is slid thru the floor and into the outrigger. Reasoning was that it prevents side shear loads. Where bolts may break or body tears off mounting plates.
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post #6 of 16 (permalink) Old 05-24-2016, 03:47 PM
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yea, matching plates underneath bolted together through the frame, and the piece going to the frame from there is what i was expecting. had never thought about putting a piece inside the cage and running that down to the frame.

i have seen cages going through the floor before, too.

regardless, i'm curious to the pros/cons so i can have that information when the time comes to do mine. i'd prefer not to do an entirely new cage if i can avoid it. the back seats fold down as of now, but i don't have an x anywhere.


these are a couple pics that show what i'm talking about


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post #7 of 16 (permalink) Old 05-24-2016, 03:50 PM
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post #8 of 16 (permalink) Old 05-24-2016, 03:57 PM
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Quote:
Originally Posted by Hillbilly Heaven View Post
Depends on how they do it. Each downtube will have a plate welded on the end of it. Under the floor the outrigger will have a matching plate welded on it that will bolt thru the floor to the top plate. Only holes in floor are for the bolts.

The other way is similar except they will cut a hole the size of the tube ID thru the plates and floor. Then a tube or I have even seen solid bar is slid inside the downtube and welded. Then this piece is slid thru the floor and into the outrigger. Reasoning was that it prevents side shear loads. Where bolts may break or body tears off mounting plates.
First way is how my 78 is, though I like the 2nd way better. To me it comes down to how the cage is deigned as a whole. If your seats are tied in to cage I would make the body able to float. If not I feel it is important that the body and cage stay in the same positions as much as possible.

Mine has been bolted in as such for 5 years or so and I have noticed no cracking around any of the plates or any other negatives. I have no rubber or urethane isolators of any kind on mine. I am no expert on cage fabrication though just what I have seen and thought from looking at other builds. I think the end use vs how easy in/put you still want to be has to be considered too.


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post #9 of 16 (permalink) Old 05-24-2016, 05:52 PM Thread Starter
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Usually the cracking supposedly occurs in the A and B pillar seams. The body will try to flex and can't, so the pressure occurs at the seams. I would love to tie everything together even at the pillars, but not at the expense of cracking the body. Floating the body would be good as I was planning on attaching the seat mounts to the cage.
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post #10 of 16 (permalink) Old 05-24-2016, 06:39 PM
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No cracking on any body panels eithier, just rust


The Street Queen: '92 Eddie Bauer- C6 Swap, Roller 357W 400hp/400ft-lbs, SCT Tuned, 4" Lift, 4.10's,
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Quote:
Originally Posted by Hillbilly Heaven View Post
Usually the cracking supposedly occurs in the A and B pillar seams. The body will try to flex and can't, so the pressure occurs at the seams. I would love to tie everything together even at the pillars, but not at the expense of cracking the body. Floating the body would be good as I was planning on attaching the seat mounts to the cage.
Oh really? That's interesting...

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post #12 of 16 (permalink) Old 05-24-2016, 07:39 PM Thread Starter
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I think the discussion about whether to tie it to the body or let the body float maybe in this link. With 19 pages to read through I will wait till my registration is approved so I can search for it.

Roll Cages... multiple threads merged - GoFastBroncos.com
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post #13 of 16 (permalink) Old 05-24-2016, 08:49 PM
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ON the cracking panels, after some more though; My cage does not tie into the body at the pillar. It has a down tube right next to it. I do get some body to cage contact in the area, as I have since put some roll bar padding there to make it so it does not make noise. Maybe I un-intentionally have made it so mine has not cracked just due to my lack of putting supports there when installing the cage. You can see what I mean in this picture


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post #14 of 16 (permalink) Old 05-24-2016, 09:04 PM Thread Starter
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That is a typical cage install. You would think at first with it attached to the frame via flanges at the floor the body and cage would move as one piece, but you have proven it doesn't. While it maybe be stiff as a whole near the floor and frame, as you move higher up you keep the stiffness in the cage but the body begins to move.

I can visualize some of the physics and stresses but not all of it. I can see where Nodes need to be in a cage for the bending moments, but not when it comes to attaching it to the body. Definitely not good at describing it.

We need one of the BroncoSpeed experts to weigh in on this.
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post #15 of 16 (permalink) Old 05-24-2016, 09:34 PM Thread Starter
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I asked a chassis builder I know, about this. While he is a Land Speed Racer and builds mostly LSR and Drag cars, I respect his opinion and expertise when it comes to chassis fabrication.

Quote:
I think it doesn't matter...it's going to shake the shit out of it no matter what. If not attached, it will flex real quick, if attached, the vibration will make it crack.
Delaware Chassis Works | A Go Fast WordPress site
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post #16 of 16 (permalink) Old 05-24-2016, 10:35 PM
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I have always done the tube chassis through the body style on drag vehicles. Most unibody and sub frame cars need to be tied in so it is necesary to eliminate chassi flex and body twist. I had a Camaro with wrinkles in the roof due to body wrap, even with sub frame connectors and a 6 point cage it twisted like a beer can. For my Bronco I am planning a super rigid frame taking advantage of the full frame rails, trussing and boxing the rails will make for a more rigid frame. Cage wise I am going with a front coil over tube cage with firewall tubes tied into the door pillar tubes and roll bar. My plan is use the cage more as a safety feature than for chassis structure due to my frame modifications. I want to minimize the obstructions in the interior so I am building the frame up to handle my HP level and reduce wheel hop. I suppose it all comes down to where you place your structural support and how you tie things in that determines whether the body is a structural component of your chassis or not. Without the body my bare frame is a wobbly twisty channel structure so the body in stock form is the only rigid component. If the body is tied directly to the frame with the cage tied in with plates and outrigger you now have a unibody vehicle. It then is subject to the stresses that would be applied to and Mustang or other vehicle of the design. In that case I would say solid aluminum body mounts would be in order to prevent flex between the frame and body to maintain structural integrity. It is much like using a rod end for suspension or solid engine mounts, yes you have less flex and more integrity but with the cost of transferred vibration and stress. When enough load is applied somethings gonna break, could be a wrinkle in the body or a snapped body mount but something will eventually give. For my truck I will use grommets through the firewall and floor leaving room for the body to float to minimize vibration as I am street driving it, if I were building a desert racer or rock crawler solid mounts and body plates would be my choice.
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