i have a 69 chevelle with drum brakes that worked fine, i did the complete disc brake conversion for the front and put the new master cylinder in and tried bleeding the back brakes first and i wasn't getting any fluid. the master cylinder is not pushing any fluid through the lines. i took the lines out and blew them out.
could this be that i need the porprotioning valve ???
or is there something else?

thanks dave

Did you bench bleed the master cylinder?

someone had told me how and i did it, im not sure if it was right though.and after trying to bleed the backs i did the fronts and those bled just fine.the back is the only ones not getting anything air or fluid...

Try to bench bleed it again. If there is an air pocket in there when it is tilted into position it will never come out.

I did a 67 4 wheel- disc conversion and it took me forever to get fluid to come out the back. In my case the proportion valve would close up and not let any fluid to the back. It works really well but when you are bleeding brakes it feels the pressure differential and it closes the rear circuit. I dont think you have that problem since you are not using one? Try opening both rear bleeder valves and put pressure bleed them with assistance. That might work.
Make sure you close the bleed screws when going back up on the pedal. Repeat ....! Also I used a vacuum pump and hooked up my Air compressor and that worked really well too, so I did not need help,only problem was I had to be quick adding fluid to M/C!! The M/C has to be bench bleed before you do the above mention suggestions otherwise it will never work.

thank you, can you give a brief explanation on how to bench bleed the master cylinder please?