87 240DL, Half of brake system will not bleed, hlp plz

Hello,

I have a problem with my 240 wagon brakes. I have replaced the front calipers and pads, the master cylinder (twice), and put in another used pressure regulator (the splitter box which divides the brake system into two parts). The first half of the system bleeds with the left back wheel, and the top-most bleed screws on the front calipers. It had bled fine, with no air bubbles. The second half of the system goes to the right back wheel and the two bottom bleeder screws on each of the front calipers. For the life of me, I can't get pressure to these lines. When I bleed any of the bleed screws on this system, no fluid comes out. Air/fluid can be sucked in ( I used a clear hose into a jar of brake fluid) but no fluid comes out. I checked and there is fluid coming into splitter box on this half of the system. I took off and cleaned two of the three other lines in that half of the system. Tried to bleed it again, but nothing. There are no visable leaks in any of the line. I am at my wits end. The brakes are'nt ABS. The rear pads are fine. Any leads would be more than awsome.
Thank you,
Glenn