Power brakes aren't power

Run car for about 5-10min. Shut car off. Wait about a hour. Pull the hose off the brake booster. If you hear a woosh the diaphragm is holding vacuum. If you hear nothing the diaphragm is bad, unles you are expiriencing the partial split that trailbeast explained then it would be hard to detect this way. But this is the easiest and quickest test to do