Welcome to the "Bolt"! You may have a crack in one of the rubber lines,connecting the manifold to the steel lines that run the frame rails,to the 2-speed diaphragm. There are 2 more rubber lines connecting the diaphragm,at that point. It's best to replace ALL of the lines, (vacuum and brake,rubber and steel),since they're 65 years old. My diaphragm was dry-rotted as well. Send me an e-mail,(since you're moderated),and I'll be happy to tell you how I fixed mine,and had FUN doing it! Enjoy your truck!!
