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[wesayso]

BellyDoc previously said:

I have 3" of suspension lift and 35" tires.



This is flex fatigue. Note that the crack is happening ON TOP. Ask yourself how to apply a one-time force necessary to get the metal to TEAR at that location. It would have to be bent OVER something with down pressure in front and behind, while up pressure is applied beneath ... or some equivalent mechanism to get this to be a point of bending. That was the thinking in guessing about wheels hitting inside the well. If the body is supported in front and behind, and the wheel pushes up in the middle, that would explain it. Unfortunately there are crumple points that are much closer to the place over which the wheel touches, and if you push up inside the well at the point of contact, you can flex the actual well, without moving the stiffer support box above. The wheel wouldn't be able to do it.

That's NOT what is happening here. The twisting motion of the frame in offroad driving conditions is only partially being damped as it is transmitted to the body. The rest of the body has a lot more stiffness because of the height from floor to roof. The engine compartment is much flatter and therefore has less vertical stiffness. The body is getting "flexed" up and down (and probably in TWIST) just like the toe of a well broken in running shoe. This bending effect is amplified at the level where the low profile engine zone meets the high profile body zone. High flex meets low flex.

This is what I've been thinking. It would be an interesting test to back off on the nuts on the forward most body mounts (near the bumper attach points) and measure if the front clip rises up at all (as measured near the front turn signals). This would indicate the kind of stress BellyDoc is talking about. This would be easy enough to check. I still believe it is caused by something out of kilter after installing lifts.