Hy Old GMC Gold, now hang on here just a second, if things were "normal" until you started the engine, then I would think your Hydrovac may be the cause of your problem. The atmosphere valve may be leaking or stuck open, this would cause the brakes to partially apply as soon as the engine developed vacuum. Do you have a manual or schematic which covers the Hydrovac?
Last edited by 3B; 10/12/2014 1:33 AM.
