i plan on back halfing the 75 i just bought, i would appreciate if any one could steer me to some books to learn the basic principles involved. I know there are prefabbed back halves and i will buy one but i think it important that i understand the basics. i alos understand i will not become an automotive enginere reading a couple of books. i just want to understand enough to ask intellegent questions of the people who make this stuff.
thanks
greg

 

When I back-halfed my 64 frame, I used the assembly manual and the service manual to ensure I maintained the correct measurements. There is a picture in one of those manuals that has all the measurements listed.

The trick is to make sure you have a level plane to reference all the measurements to. I built a level rectangular frame to use as the level reference and tacked the frame to it before I cut. I measured everything before the cut and compared these to the measurements in the manual to make sure I started in the correct position. Then I cut the back off and put the new section on this frame and tacked it to the front half. When welding, you need to do small areas as the frame will warp as the weld cools if you do a large area (I found this out from experience). Measure, measure, and measure again. If something appears to be off a bit, you can always grind out the weld and do it again.

It's a bit tedious, but it can be done by a DIY'er. It was only my second frame job, the last one was 20 years ago, and my final measurements were within .040" of the factory specs.

Good luck.

 

Subfixer has some good pointers for a do-it-yourself effort. I took mine to a retired frame guy who had opened his own shop and he did it for me. There are a couple of lessons learned I have however, I used a new back half and found that the two rail halves on the new one were not overlapped and welded to the exact dimension as the old frame. I took a cutoff tool and cut the welds on the reaf half that hold the two rail halves together. This way they had some movement and they could be lined up at the splice line. The very slight taper to the rear on the backhalf that resulted couldn't be seen and the frame sections lined up pretty well. I also drilled the holes in the frame section on each side of the splice and had them plug welded up to the sleeve. Very strong splice. For what it's worth I ground the welds and used All Metal to smooth things up and it still looks like new today. Since mine was at a frame shop anyway they put it on their fixtures and did a little work on the passenger side front rail where is had been hit before. With these new laser levels that are so common now, it should be a lot easier to check your frame out to a datum level and determine if you need to have any final tweaks done on it by a frame shop when you are done.

Dan

 

I had to do the same minor surgery to my new back half as Dan did. I also plug welded the internal sleeve in 4 places on each end.