Make sure all lines are super tight with no leaks or air able to get in.
Bench bleed master cyliner before installing....
Make sure mc rod isn't to long...
Make sure the bleeders on the calipers are on top...
Adjust rear brakes very tight, the pads should be dragging on the drums...
Bleed brakes from passenger rear, drivers rear, passenger front, drivers front...
If all this doesn't work, then you have a bad MC or...