Just finished mine and I stretched the rubber as I went around the corners. Take your time and it will come out just fine. As I pulled the seal I squeezed it together at the same time.
I just did mine, I had Hot Rod Glass cut it for me, Carson recommended a drop of super glue at the areas that pucker out, I tried it and it worked great, take your time and use a razor blade to trim off the glue after it sets. You have to glue, then hold it down with your finger for a minute to two, same with the quarter glass.
Perhaps not ‘taut’ enough ? I’ve just done mine with 40 year old rubbers, and took a bit to try and flatten them out first and try to reshape them as I went. A few others on this forum also suggested the superglue tip.
Just found a store open that had super glue. Dap brand was the only one that listed glass and rubber.
You have to pull it pretty hard. I only used super glue at the point where both ends of the seal meet.
The Jalopy Journal
