I have been having some brake issue on my 78 Blazer (low brake pedal, hard to stop). I bleeded the brakes several times and got all of the air out. When I hit the brakes, I hear a gust of vaccum air comes out around the brake pedal/booster area when I pressed on the brake pedal. I think the problem maybe the brake booster. Does anybody know how to diagnose a vacuum operated brake booster? I am about to give up on this issue and thinking of upgrading to hydroboost instead. Thanks in advance.