Rear crossmember: original or 4" channel?

I am contemplating replacing the crossmember on my '70 because it is very cobby. I have looked at the repo ones, seem pretty staightforward, around $80.00, IIRC. A piece of 4" channel is about $20.00. I am planning on setting up some sort of rear mounted swing-away spare mount. Just wondering a few things:

1. A "C" is torsionally more rigid than an "L"; this and the increased thickness of the "C" channel would seem to reduce frame flex. Knowing that the frame is supposed to twist some per design, would the introduction of the "C" channel adversely affect the function of the frame, perhaps to the point of introducing stress risers somwhere else on the frame, and will it hurt the off-road flexiness 5s are known for?

2. The stock crossmember is pretty flexy, although my original one is a two layered thing. Are the new ones, also two layered? And, if I use it as an anchor point for my spare tire rack, is it going to fail (crack) when extra load is introduced?

Am I thinking too deeply on this? :?

 

If you are planning a big tire carrieir and rack, use the 4" channel. Tie it in to the frame well and you'll never have trouble

Just my humble opinion, though...

 

As a side note the replacement rear channel that firefightermike bought from Krage is 50-60% thicker than the stock one and its not a 2 piece unit. The factory unit is a formed C channel except at the very ends. My 71 model rear crossmember is not a 2 piece design. You may not have afactory unit, is it rivoted to the frame or bolted?

 

It is riveted. and I stand corrected, part of it is "C" and the outer endges are "L". Still 2 piece.

 

I used 4" channel before and tapered the ends up like the stock unit

 

thanks for all the help!

 

I integrated mine into the bumper, rear body mounts, tow points, roll cage frame tie in and receiver hitch. I used 3"X1/4" angle. I have no doubts that mine would support a tire carrier. But I do have some concerns forward of the 3/4" bolt hole as that is where the flex will be moved to. I have been keeping an eye on it. In fact, I have inspected my frame very carefully every few hundred miles since all the work I did to it. Just want to make sure I didn't make new stress points. I haven't had it out and wheeled it hard yet but I hope to soon.

 

that is sweet...........

 

so that completely replaced your crossmember? what about the outer body mounts? any problems eliminating those?

cool tire rack BTW.