[my new 72]

Just what the topic says'. My truck is a 72 with power brakes, and I am having a bit of trouble. I just put new calipers on my truck and I can't get my brakes bled. I have tried everything. I tried to gravity bleed them, I got one of those vaccum pumps, I had my wife pump the snot out of them, and still no luck. The master cylinder never ran dry, so I know that is not the issue. I get a lillte bit of air out of the system, but it never stops. I can't get it to run solid fluid. I have not bled the rears though since I thought that since the master is seperated, then I did'n have to. What am I doing wrong, and where could this air be coming from??