Disc/drum rears locking up?

[rski]

Problem Rears locking up.Front Baer serious street 2 piston calipers rear stock drums,Master 7/8 bore from 76 Monza . Master reservoir is reversed the front bowl is smaller then the back.Ran the back of the master to the front of stock junction (drum/drum) front of master to a wilwood adjustable proportion value then into the juction block.Bleeding the rears with the valve fully open we get very little flow and can hear sucking when bleeder is opened up.Fronts bleed fine.Even with the poor bleeding of the rears they lock up before the fronts,even with the proportion valve fully adjusted in. Had the same problem with a 1" master stock drum/drum junction rears would lock up first.



Any suggestion? Thanks