rear frame crossmember/panhard attachment
 

I noticed while I started my frame prep that the frame crossmember that has the panhard bar connection point on it is about 1 1/2" offset from where it attaches side to side (shorter on the pass side I think) (red lines). While the rear measurements are exactly the same (blue lines)

This seems to be from the factory as while the frame is slightly out of square (1/4 - 1/2"), the crossmembers are all still factory riveted. Does anyone know why this was done? At first I thought the frame was way off or something was bent but measuring from rivet to rivet shows a definite change.

Re: rear frame crossmember/panhard attachment
 

Unfortunately I don't have an answer to your specific question, but I can tell you it's not just your frame. My frame looks exactly the same as yours, and every frame for these trucks I have ever seen has the same skewed crossmember.

Re: rear frame crossmember/panhard attachment
 

I've noticed that they are all that way. I think it might be angled for the panhard bar to be able to move up without hitting the cross member. My dad thinks it's angled for the tire carrier. Messes with my head every time I see it!

Re: rear frame crossmember/panhard attachment
 

As I understand it, it's angled for ladder type rigidity.

Re: rear frame crossmember/panhard attachment
 

GM angled this crossmember to prevent the frame from "racking" like a ladder frame would naturally want to do. This is an engineering design.

Re: rear frame crossmember/panhard attachment
 

I don't mean to question anyone's intelligence or start an argument, but the slight angle of that skewed crossmember does not look sufficient to have any real effect on the frame's potential for racking. Seems more like it's meant for clearance, or something along those lines.

I'm admittedly not an engineer, but I am an engineering technician, and have spent every day of the last 9 years drawing structural plans for the same firm. Diagonal bracing meant to resist racking in a rectangular frame is typically positioned at no less than 45 degrees.

Re: rear frame crossmember/panhard attachment
 

In my opinion the crossmember is angled for clearance with the panhard bar should it come up that far.