Intermediate vs. Early frame question

Hey guys, I did a search but didn't find an answer to my exact question. I just picked up a '73 frame from a forum member, and was planning on using it on my '57 project. The end result will be something similar to "Posi's do-over".

What major differences will I need to overcome to mate this frame to my early Cj5 chassis? I understand that the frame is 3" longer behind the front spring perch, so my thought was that by moving the front spring perches forward to the end of the frame, and the rear perches backwards, I should end up with 9" of stretch with no other discernible differences. Am I off track?

I purchased this frame because of the reinforcements that were done by the factory in the 70's, feeling that this is a better frame than my beat up 1957 frame. It also had the rear tank still installed, even though I'm planning on putting a YJ tank with left fill in its place. I also have a 1969 frame in ok shape that I'll use for motor mounts unless someone can convince me its a better choice than the '73 frame.

 

Ok, if you put the '57 tub on the '73 frame, it will sit on with no major changes. The difference is in the length of the frame ahead of the firewall. The springs are the same length for a '57 and a '73, so I don't see how you are going to stretch the WB more than 3" without extending the frame beyond the tub and front fenders. Your '57 fenders will be too short by 5" for the '73 frame ahead of the firewall. The '73 front clip is lengthened 5", even though the WB is only stretched by 3".

 

hmmmm, once you put it that way, 5" seems like a big difference in the length of the clip. However, I seem to recall that the intermediates had the grill closer to the bumper than the earlys, is that true (I'm guessing 2") ? That might negate some of the effect of the stretch. As far as where I got the other 6 inches of stretch, I was thinking of moving the spring perches to the very end of the frame, since they sit a few inches from the end now.

 

Have seen people build rectangular tube bumpers and put the shackle mounts under them.

 

Hmm. From my memory, it does not seem to me that the shackles are that far from the end of the frame.

Here's the front of my CJ-6 -



It has a winch bumper here that extends the frame horns out a few inches, so length of the frame isn't so clear. Note that the wheel placement is 2" further back in the wheel well than on your '57. These Early CJs already have trouble catching the front lip of the fender, and if you move the spring further forward than that it will be worse. Plus, I thought that the frame horn only sticks out maybe 2" beyond the spring hanger - just enough to mount the bumper. Unlike the '57, the '73 frame does not use the bumper for structure, so it's just a bumper.

Well, no pic of the rear. Pretty sure the rear hanger is really at the end of the frame.

Ok, here's a picture of a CJ-3B body on a CJ-5 frame. Looks to me like there is no room to move the hangers rearward.

 

That photo of the CJ3B tub on the CJ5 frame looks just like my 57 CJ5 frame did under my 48 CJ2A tub (it was done way back before dad bought it in 62. I cut the CJ5 frame down to match the tub and restructured the trailer hitch support to switch over to a 2" receiver style hitch. I had to make long shackle mounts to end up with the shackles pivoting right below the rear cross member (they are CJ5 springs 81" WB)

 

Mark, you're on the right track with my intentions for the rear stretch. I was planning on incorporating a rear 2x4 bumper, and integrating the shackle mounts to the bumper.

 

Later model cj shackle mounts would fit your bill. Not nearly as stout as what Mark made but, the same basic theory.

http://www.quadratec.com/products/5...oglemerchant&gclid=CIy3nvvQk8oCFcwWHwodoCwPtw


This is what is was going to use, when I thought about building another jeep. They are for the wider 2.5" (?) springs though.

 

I have the ability to carve up steel pretty good so I tend to design things with that in mind. I also tend to over engineer the crap out of just about everything.