I'll provide as much info as I can, so this might be a little long. I'll just break it up into sections. VEHICLE: 72 Dodge Demon 340, purchased it back in 2013 with I believe a right stuff manual front disc brake kit. Decided to install the Dr. DIFF setup for better braking and liked the looks. The brakes on the car have always sucked since I got it. First manual brake car so I wrote it off as that. Didn't really have issues with the install but we cannot get the air bleed from the brakes. ISSUE: Didn't really have issues with the install. At first we could not get the fronts bled. We traced that back to the matser cylinder. It's a Mancini retro fit, the two bowl master cylinder with adapter plate. I am not sure which bore the master cylinder is, 1.032" or the 1.125". We seen the brake lines where reversed on the master. The master was installed on the car years ago and has been ran like that since. Hence the crappy braking. We pulled the lines, reflared them since they only had a single flare not double, and reinstalled and tried bleeding again. Our issue moved to the rear brakes now. We tried bleeding the porpotioning valve to the rear and worked our way back. We are still getting air and we are starting to think the master cylinder may be to blame. QUESTION: with having the 13" front disc brakes and rear drum, what master cylinder is recommended. This is still a manual brake car. We have no drips, anywhere on the brake lines, proportioning valve, wheel climbers, or calipers. We can't figure out where we are getting air in the system.