I installed the disc brakes from a Dodge Aspen to my 66 Belvedere and that was pretty simple... I did replace all hardware,, shoes pads and drums along with a power brake and booster that is re-manufactured. The proportioning valve was used from the donor car.I left it sitting for a few months as I got busy with other things. When it came time to get back on it I got a power bleeder and proceeded to bleed all the brakes starting from the far rt. rear to the left and up front till all I was getting was brake fluid and no air. What is strange is that the rear brake fluid reservoir will drain down when I bleed the front brakes and I cannot get any pedal pressure. I am certain after going over a number of times that the routing of the brake lines are correct and that there is no leaking in any of the fittings. I do get fluid from all four corners. If I pump the brakes a bit I can get pressure to stop the car at slow speeds. I did not pre prime the master as I faulted and forgot I didn't do it on initial install. I hope I have given enough info so someone sees what I am missing.