Sometimes it's Easier to Start from New
Rear leaf spring conversion, Part 1: Rebuilding the rear frame
When I first bought the 4Runner I knew it had a lot of rust but was unsure how bad the frame actually was. After the body came off I could tell I was in for some work. The coil spring buckets and the frame beside them were completely rusted out. The pan hard bracket and some of the link brackets were also badly rusted. I was considering cleaning and fixing all this rust before I started thinking of an easier solution. I needed to free up some room for the fuel tanks and spare tire carrier.A leaf spring conversion would get rid of the suspension links and free up more room for my fuel tanks. It would also give me the room I needed to build my spare tire carrier. I'll have a artical about the carrier and tanks later, or you can check out the design page if want a sneak peek.
After approximating the work required to fix the existing frame or just build a new leaf setup, I decided building new would be faster and easier. The extra room would also be a plus for what I had planned.
I cut the frame a little ways behind the C-Pillar body mounts. I made the cut very long in order to give the splice lots of weld surface and strength. The outside of the frame rail is cut at an angle, the inside is straight. This makes the joint stronger by not giving it a single plane of weld surface to crack and shear. I used 2"x4"x 0.120" tubing for the new frame rails. I had to flare out the 2x4's for them to match up with the existing rails. I made them longer then what I needed so that I could correct any errors when I measured and cut them to fishished length.
With the extensions welded on I leveled the chassis side to side and front to back. Then I spent a great deal of time measuring the leveled car body and then frame to make sure I placed the rear frame rails at exactly the right height. When everything was squared, measured and marked, I cut the extensions at the proper angle. Then I made up some oversized rear frame rails and welded them on level and square. I didn't make this joint long like the other because the cross member will be overlapping it and the outside will be fish plated for strength.
With new steel in the back it will be easier to weld on the spare tire carrier and rear suspension. It also will fit the contour of the Integra belly better.