I have a simular crack under my rear seat
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I am trying to picture what motion can cause this crack. I am thinking flex of the rear end of jeep up and down might do this. Prior to adding the center stiffener, that kind of bending might have been absorbed over the full wheel base, but with the center stiffeners installed, well the center dont flex much now, cant absorb the stress by flexing, so all the stress now is getting concentrated behind the rear end of the center stiffeners, which is under the rear seat.
I got 33x 12.5 tires 5.5 inch lift, 4.11 transfercase low range, Ford 9 inch rear.
Now if I do rear frame stiffeners and tie them in well with the center stiffener, then this area should see a lot less bending from up and down motion. However if this crack is from a twisting force (as in one rear wheel up, other rear wheel down) then rear stiffeners may not be solution, rather some sort of cross member to withstand the twist maybe needed.
What say you all?