Don't pry on the pads. Use a channellock pliers to squeeze the ears of the pads against the body of the caliper, from one side a little and then the other, AFTER making sure the bleeder screw is open slightly to force out fluid from it, and NOT push bad fluid back thru the sys. I would put some PB Blaster around the threads of the bleeder screw a few days ahead to help loosen it, too.
Vac. ga. tests upper engine stuff, like valves and certain vac. leaks. Its the poor man's diagnostic machine. Use it for non-blown engines as a very easy tester.