cj7_304 More on rollcages.. - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 08-23-2000, 08:10 AM Thread Starter
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cj7_304 More on rollcages..

[img]/wwwthreads_images/icons/tongue.gif[/img] About using a "sill".......In 1971 we were running two flatfenders up a goat trail in the mtns above Fresno and my buddy's Jeep blew a front driveline on a real hard up hill climb. The Jeep went immediately sideways and rolled quite a few times, killing him and the guy with him. One of the things that happened was that the tub deformed badly and the rollcage drove down through the floor. The tub stayed attached OK, but the cage lost all of it's protective shape. When I looked at the photo recently of the white CJ, I could see yet another rollover system problem and that was that the bars did not connect securely to the chassis. It so happened that the last few months I have been working on upgrading the four most critical frame-to-body mounts on our CJ-7, and the wreck in 1971 was in the back of my mind while I was scheming on what to do. The MAIN hoop in the CJ system......as manufactured.....does not have good lower support. The CJ frame mounts are cantilevered off the frame, and must take the downpressure AND the rotational force which tries to peel them off. That, PLUS the small bolts that connect the bar to the body and not actually to the frame, prepares the CJ for the scenario demonstrated in the recent photo of Mike Lane's rig. Even before Mike's incident, I had designed a "sill" which went crossways in the tub at the step in the floor; was 5" tall and 3/16" thick; was through-bolted to extra plates set behind the body crossmember just ahead of the rear tires; and THOSE plates weld to a thick pad which replaced the original captured body nut. The "sill" provides sectional strength for downpressure, and keeps the rotational force from trying to peel off the fame mounts. Additionally, the sill gives the tub more than just the two spots of support that the captured nuts gave, and finally, the thick pads allow bolting the roll bar direct and not just to the floor of the tub. When the ROPS [Roll Over Protection System] is in place, the "sill" is the bottom of the block "O" formed by the tub and the main hoop.[img]/wwwthreads_images/icons/tongue.gif[/img]

CJDave
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post #2 of (permalink) Old 08-23-2000, 09:13 AM
 
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Re: cj7_304 More on rollcages..

Dave...excellent description! I think you need to get one of those digital camera's to take some snap shots. That way
we can all see what it is your describing. I think I follow the scill idea, but how does it contour to the shape of the floor?

Alec

'78 CJ7 258 T18/dana 20 dana 30/amc 20 w/ mosers & lockrights
'glass body tied in full cage

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post #3 of (permalink) Old 08-23-2000, 09:31 AM Thread Starter
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Re: cj7_304 More on rollcages..

[img]/wwwthreads_images/icons/smile.gif[/img] The "sill" follows the VERTICAL PORTION of the "step" in the CJ floor. It is simply a thickening of that part of the tub, and a way of giving some "beef" to it. You could actually have a "sill" as a part of the demountable rollcage hoop at that point, but it really is more practical to have it as a part of the tub. We were battling some rust in our CJ, and the sill solved that problem as well. So you have the part that is crossways and attached to the vertical part of the floor; and then the two pieces in the back just ahead of the wheels; tucked into the CJ body crossmember; and then the heavy pad that takes the place of the captured nut. Our new body bolts [in the four critical spots]are 1/2" N.F. Gr.8, The CJ ROPS bolts to the heavy pad with bolts down thrugh the floor, and it also bolts to the sill and through to the pieces that were added in front of the wheels.[img]/wwwthreads_images/icons/tongue.gif[/img]

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post #4 of (permalink) Old 08-23-2000, 10:52 AM
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Re: cj7_304 More on rollcages..

I have been following these rollbar posts for some time now, and a question I have asked in the past, I am still confused by. Please, call me stupid, do whatever, but please help me understand the mechanics, and the related dynamics, of installing a roll cage to the frame, through the body. CJDave, I saw your comment on needing different size feet on the upper and lower sandwiches to prevent the "cookie cutter phenomenem".

My observations are; The body is bolted to the floor via mounts that allow limited independant movement of body and frame. Any bar solidly attached with a sandwiching of the frame will not allow this independant movement.

Now the questions? Should the original body mounts be replaced with solid mounts, or should some type of rubber mount be fabricated for the sandwich, some type of sheet rubber on both sides of the tub, kind of like butter on a sandwich? Or, does the rollbar stiffen the frame sufficient that flexing of the frame becomes a non issue?

My concern is if I don't do something here, I will end up greatly accelerating the destruction of the sandwich/body mount areas.

Just call me really concerned! Safety is important, as is the overall jeep structural integrity.


Enjoying Montana's Big Sky (NOT, Fire Fire Everywhere)
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post #5 of (permalink) Old 08-23-2000, 11:05 AM Thread Starter
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Re: cj7_304 More on rollcages..

[img]/wwwthreads_images/icons/tongue.gif[/img] Nope.....you don't de-isolate the body. You continue to have the rubber pad isolators just as you did in the as-built condition. What you DO change is the way that the roll bar connects to the body. In our CJ, I was concerned that there were TWO separate connections between the roll bar and the frame. Of course I was not able to look at the frame of the white CJ in the photo, but I SUSPECT that the small 3/8" bolt that went from the body to the frame broke under load. What we have tried to do is establish a heavier-than-stock metal pad in place of the original body-mounted captured nut, and then bolt THAT via the rubber pads to the frame mount with a larger, stronger bolt. The pad also is the ANCHOR for the roll bar foot, which now removes the body from the "system" since it is no longer the sole support of the roll bar. So visualize the Jeep with no body. Attach the roll bar to the strong, rubber-mounted metal block and you have the "System".[img]/wwwthreads_images/icons/smile.gif[/img]

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post #6 of (permalink) Old 08-23-2000, 06:32 PM
 
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Re: cj7_304 More on rollcages..

The rubber engine and transmission, or rubber body mounts, and washers from any large truck (semi) should do a great job of being body or roll bar isolators.
They take a huge beating in class 8 trucks, and should hold up in this application.

If they will hold a Mountain Mack together hauling coal in the mountains for a million miles literally, it should hold the body and roll cage of a jeep....
Mack body mounts aren't double cup either, so they would be perfect.

I use them for generator/ welder feet, and I have yet to have to change one in 15 years.
They have those huge washers with them, and those washers are so hard you have to use the plasma cutter to make extra holes in them.
I think the stock hole is for a 1/2" or 5/8" bolt.... Just about perfect...

CJ Dave, I never thought of using rubber isolators for the roll protection system.
I was thinking in the box, the race car box, that frame and roll cage had to hold the body in place when both were attached solid.

I've been kind of thinking the last few days that I needed to think of a way to rubber isolate the cage and body, but you just put it together for me.
I hate rattles, and if the tub were attached directly to the frame via the cage, everything would be loose all the time, and rattle...

You learn something every day!!
Thanks for the great idea Dave!

"I Have The Body Of A God... Buddha"
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post #7 of (permalink) Old 08-23-2000, 06:57 PM Thread Starter
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Re: cj7_304 More on rollcages..

[img]/wwwthreads_images/icons/tongue.gif[/img] Yeah, I know what you mean. I had to crank my thinking away from "track" and think: "Highway". In the race cars, we built the frame and cage as one integral unit, and one braced the other. It was a lot easier when the cage width and the frame width were the same. I am seriously considering a cantilevered ROPS for the CJ since it would not have the problem of getting around the dash. I would rather use huge tube and no front drops than have small tube with drops. See my post to cj7_304 on the "sill" thread.[img]/wwwthreads_images/icons/crazy.gif[/img]

CJDave
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post #8 of (permalink) Old 08-24-2000, 12:10 PM
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Re: cj7_304 More on rollcages..

I have been looking into this for a while, and the thought that I have is to mount all of the cage points via poly bushings with the tub mounted rigidly to the cage (if you can call what I am using a tub). This should still give me a little flex as well as vibration control. The other thing I am looking at is using a "halo" style bar rather than the convential front and rear hoop style.

Another concern that I see with most Jeep cages is the windshield area. That is one big opening with no support, and it worries me that in certain situations that the front bar could cave in toward the occupants. I have not come up with a practical means of supporting the front hoop to prevent this (practical meaning not taking up occupant space). I could use a few ideas so I can start on some drawings.



Dan
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post #9 of (permalink) Old 08-24-2000, 12:21 PM Thread Starter
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Re: cj7_304 More on rollcages..

[img]/wwwthreads_images/icons/tongue.gif[/img] I tell ya, BJ....the more I think about it, the better the cantilevered bar looks. It is the "halo" effect that you mention, AND doesn't get in the way in the dashboard area.[img]/wwwthreads_images/icons/crazy.gif[/img]

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