So I just got done replacing all 4 calipers and put on stainless brake lines. So my problem is that I bled the front brakes no problem no more air. When I went to do the rears it took a long time to get a steady stream of fluid to come out because the proportioning valve was stuck shut so I pumped the shit out of it and it finally opened. I spent like 20 minutes bleeding the rear brakes and I still can't get all the air out of the system. It still sounds like there is air in the lines up by the master cylinder. I don't have any leaks anywhere. So I'm wondering if any of you guys have had this problem and what you did to correct it? The weird thing is if the master cylinder was bad the front brakes would have had air in the lines consistently too. Just to mention too that before I replaced all the brakes my brake pedal was fine. Any ideas would be much appreciated.