Finally!! Got the channels out. But remenber this, I only did one side at a time. Before the new channel was installed, I had to do some prep work. In the process of removing the channel, some damage or should I say disfiguration of the body's sheetmetal occured. One example would be the section below the rear side window. Now was a good time to take a dolly and reshape the metal back to its original shape. After I was please with the body, I installed the new channel to see how it would fit. Putting it in was easy because the body was still seperated from the chassis about 4". I just slid it in. Once in, I lowered the body. Now I could see how everything lined up. Before the welding started, the channel was removed, and ALL areas that were going to be welded were cleaned with a wire brush. If there's any advise that I can give you is to clean, clean, clean. It's hard to weld over paint or primer. Then I reinstalled it, lowered the body and installed all of the bolts that holds the channel to the body.
This was my first experience with a MIG welder. Before I started to weld the channel, I experimented with the old section that was removed. After practicing on a couple of dozen welds, I decided that I would give it a try. The first weld was kind of scarry. Didn't want to ruin the new metal by burning a hole in it. Well, it went OK. One problem that I did have was once the welding shield was lowered, I couldn't SEE a thing. Talk about welding blind! What I ended up doing was getting a #8 glass. That really helped. Something else that I did was to put a "clamp light" with a 100w bulb, on the area that was being welded. By lowering the shield and waiting a few seconds, my eyes adjusted to the "dark", then I could weld. I started with the front pillar. Ran a few beads there. One area of the pillar had about a 1/4" gap where it met the new channel. How this was resolved was to run three beads. The first bead was put directly under the gap. The second bead was put right next to it. On the third bead, it was placed right on top of the first two. As this was being done, the bead was now high enough to grab the old sheet metal. Worked great!
On the rear section, I tapped the sheetmetal down until it was on the channel. If you remember, there were holes where the old spot welds were drilled out. I selected a hole that was tight to the channel. I ran a bead in a circular motion starting in the middle of the hole working outwards. This takes about 2 seconds to do. I found it easy to do if I just concentrated on the hole. Don't worry about whether the sheetmetal will be welded. Believe me, it will. Once the first hole was welded, I skipped a couple of hole and welded another one because I didn't want to get the metal too hot. After that section was done, I did the rear area of the channel where it meets the back of the body. From there I did the section on the outside where the running board goes. For cleaning up the welds, on an opened area, I used an angle grinder with a 1/4" wheel. These wheels are great. If you gently push down on them, then of course they won't remove much metal. But. if you bear down on them, they become real aggressive. So be careful!! Don't get over aggressive.
For blending in those three beads on the front pillar, what I found that worked really good for me were the carbide rotary bits. They come different shapes and sizes. I used the one that was about 3/8" in diameter and had a rounded end. Another one that worked well was one shaped like a cone. You can blend in welds nicely with these bits.