TrollHammer

I keep running into posts about how much strength/rigidity/etc the top of an XJ adds to the frame... how the frame's gonna twist or taco without the top (or major reinformement with multiple frame stiffeners and a full cage) and so on....

But has anyone's XJ actually folded up without the top on it? Has anyone's frame actually "tacoed" due to a lack of stiffeners (rust notwithstanding)?

I have my own personal theories on the cherokee, some based on gut feeling and some based on experience. Skip this section if you dont want to hear it. I had a parts jeep a few years back that I had some fun with before scrapping it out. It was complete minus the top (and seats, interior, stuff like that), and after stripping the bumpers and doors for other things, I figured Id have some fun before I pulled the drivetrain. I then proceeded to bomb around the yard in my "convertible XJ" sitting on a block of wood in place of a seat. The suspension was unmodified, and there was nothing reinforcing the frame. I proceeded to climb a 4ft dirt "cliff" left over from excavation at a variety of angles, straight on, 45 deg, etc, and didnt have the slightest sign the thing was going to fold on me. It never did. I think XJs get a bad wrap for being "unit body construction", since the same "unibody" moniker is used for everything from monokote aircraft fuselages to K-cars. Where a K-car will fold in half if you accidentally try to jack it up in the middle (guilty), an XJ can be used as a see-saw pivoting on its frame (guilty again). I think that, as it was pioneered in the 70s before unibody had really become a popular construction method, and designed by Jeep at that, its quite a bit stronger than it gets credit for.

Anyway, what Im trying to figure out is exactly what kind of stress (how much, at what points) the top of an XJ actually experiences. Im planning out something a little wild for a cage for my wheeler and would like to know if the flimsy sheet metal of the roof actually does much to keep it from twisting, or if there are significant lateral stresses kept in check with the web of sheetmetal? After seeing pictures of roll-over damage and observing cutaways of the pillars Im not convinced there is as much significance to the roof as many assume. (Not that there is no impact, just not as much impact as some believe).

My plan for a roll cage would effectively remove the upper sheet metal of the cabin, replacing it with a removable fabric cover, as this seems much simpler and more useful than trying to patch the sheetmetal back in.

SuperRA

Isn't a commanche like a cherokee without the top body in the rear?

mschi772

If you were to look under an MJ, you'd see that it has a slightly different frame, too.

OP, if you have a good quality cage, I'd guess that you'd be fine going topless, but I'll let more experienced guys weigh in. Pirate4x4 might have guys that know more about something this extreme.

rusticon

i have seen pictures of a fully stiffened xj that was indeed tacod so yes it does happen and when i just recently stripped my old xj which had main stiffeners only and a hefty front bumper it would only sit on 3 of 4 lift arms

LiamLikeNeeson

I have a stock 89 XJ and I just went wheelin on some easy dirt trails within only minor bumps that affect roll and the roof did tweak a little bit as the cross beams on the roof are now separated from the roof itself. But the roof is still in its original shape without a fold. So I guess it could, in theory, taco without a roof but it won't be easy to do it. You might need to have a pretty decent incline or decline in the trail and going fast enough that the inertia of your jeep hitting that incline or decline would taco the frame. But if you are going slow I doubt it would be easy to do. The frame might flex a little bit like mine did but then go back into place. The roof seems too flimsy to hold weight like that so the stiff truck frame the XJ has must be very sturdy.

LiamLikeNeeson

I hope that made sense. ADD makes it hard I explain things gmvgp7kD

TRCM

Think of the xj body as a box....take a box, and open it up all the way, then set it down on a table with the open end facing you, and the side on the table top.

Ok, the side on the table top is the frame, the side to your left is the windshield frame, the side to your right is the back hatch frame (not necessarily the hatch itself), and the side left is the roof.

Now, all 4 sides are connected, and lend support to each other. so when 1 moves, the other move in unison, giving support to each other.

What happens when you remove the top ?? The front & back sides can easily move in different directions, and the bottom now has lost support from the front & back, since nothing ties them together at BOTH ends, and would be much easier to damage.

That's kind how the body would work without a cage if you remove the roof. Not guaranteed to bend/break, but very much easier to do so.

extrashaky

The Comanche has a uniframe construction in the front, with a full-strength frame behind the cab under the bed.

SuperRA

Ah I see. I never really looked into it that deeply.