I had rot in the last two inches of my rear frame rails, and the rear crossmember was mostly rot as well. I had to cut off about 5" of the frame rail ends till I got to metal I felt comfortable welding to. CAUTION!! I am lousy about in-process photos, so I apologize in advance for pic quality and the fragmentary nature of the pics.
So, first I fabbed new frame rail ends. I had to split some 2x3 tube, machine the two halves, weld them together, then machine the height and width to match my frame rails:
Then I welded in steel blocks, which I drilled and tapped for the shackle mounts:
Then I drilled thru holes and welded steel pipe inside for the frame tie in bolts:
So, frame rail ends done, I fabbed up reinforcing plates for each rail (top, bottom, left, and right sides of each rail):
I also made some angle brackets for frame tie-in's (one on each side of each rail. (No pics of those).
Then I clamped the new rail ends on and tacked and butt welded them on:
Then welded on the reinforcing plates:
Inside of pass. side rail:
Outside of driver side rail:
As you can see, I put the frame tie-in bolt holes too close to the end of the rail, so I only used the forward holes. I ended up welding everything in place anyway. Better safe than sorry
If you are wondering about the slag and spatter, I used a 220v stick welder. I have a MIG, but it is only a 110v. Once the frame rails were complete, I fabbed a rear crossmember out of a piece of channel (3/8 x 1-1/2 x 4"). This is the only pic I have of it in process:
In that pic I have the body lifted off the frame so I could weld underneath. The bottom edge of the tub sits about 1/8" above the crossmember when I finished. I put a piece of rubber U-trim around the bottom edges of the tub to close the gap. If you want I can take some "finished" pics, but with the bumper and spare tire carrier on, you can't see much.
Overall, I rate this repair as a success (except for the bolt holes at the ends of the rails, darn it!). When I jack up the rear end I put the jack on the bumper without even thinking about it. This frame repair also beefed up the rear rails so I feel much better about the frame tie in I did for the sport bar.