Had similar issues, the front brake line at the master has a residual pressure relief valve, make sure it has been removed for your front disc brakes, the valve is for disc brakes, even though I had replaced my master with disc front rear drum the remanufactured mac still had a residual valve, I cant recall who on here brought it to my attention, but I removed front line, screwed a sheet rock screw in and pulled the residual valve spring out, tah dah, fixed, when I tell you many dollars in new masters/ calipers/portioning valve and brake lines to get to a simple fix. Check it out, you may be pleasantly suprused!