Q. Most of the U-shaped channel that surrounds the trunk opening on my car is gone due to rust. This is where the rubber trunk seal goes. I have both a metal brake and a set of shrinkers and stretchers.
1. How do I go about making and attaching a new channel?
2. Should I try to bend a complete U-shaped channel or just an "L" shape, and then weld some pieces together?
3. What is the best sequence of operations for making a new channel?
Charles Fennen
Via the Internet
A. This kind of damage is very common on older cars. With a brake, and a shrinker and stretcher, you can reproduce a channel. It's an intricate job, but if you work slowly and carefully, you will succeed.
The first step is to carefully measure the existing channel. Starting at the inner edge, there is a vertical flange, then a flat that forms the base of the channel, then another vertical flange that comes up to meet the surface of the body in the area surrounding the deck lid. Knowing these dimensions, you can cut strips of metal to be bent on a brake to duplicate your channel. It is only feasible to work with 'L'-shaped pieces of metal, so I would make one 'L', or angle, that comprises the inner flange, and the base of the channel. These pieces can be any convenient length, ideally they would be long enough to span the distance between the rounded corners, so that you can keep your welds at the corners, where they are easier to blend, rather that in the center of a long straight run.
You'll need to make another angle which comprises the outer vertical flange, and then goes out at least 1/2 inch to blend in with the surface of the car body. This means you will have a weld bead 1/2 inch away from the channel, in all places where the channel is being replaced. It is much better to have this weld 1/2 inch (or more) away from the channel, rather than trying to weld right on the corner where the channel starts! Welding on an edge is fraught with problems, and you'll find you have much better control over the shape of the parts, and you'll get much less distortion, if your weld is away from the edge.
With the two sizes of angle bent to size, you can use your shrinker and stretcher to contour them to the proper shape. I'd keep the old channel (or what's left of it) in place until all the shaping is done, and then replace one section at a time. A very good technique is to lay the outer portion of new angle over the old channel, scribe a trim line on the body, and when you cut the old channel off, cut one material thickness past the scribed line, deeper into the panel. Then, when the new piece is butt-welded into place, it will be in exactly the same position as the old channel, so the gap between the deck lid and the body won't change.
You'll have to do this scribing before the two pieces of the new channel are joined, otherwise the new channel won't fit into the old channel, but it's preferable to join the two angles (completing the channel) before they are welded into the body. This will give you much better access for welding the angles together-it's much easier to weld on the outside corners where the angles join, rather than the inside corners-and you can make a smaller weld bead on the outside, which will give you much less distortion. Also, this will allow you to straighten the channel before it is installed, in case there is distortion from the weld.
After you have the two angles welded together and have done any necessary straightening, you can trim away a portion of the old channel, and tack-weld the new channel into place. After all sections are tack-welded, check the fit with the deck lid, and make any adjustments before you do the finish welding. Because of the tremendous strength the channel section will have, it's unlikely that any of the finish welding will cause the channel to warp, so you should only have to do a tiny bit of straightening right at the weld bead on the body skin, which can be easily done with hammer and dolly work.