No rear brakes 65 C10

[mrdave03]

Hi All, I had done a front disc brake conversion about 5 years ago on my 65 C10. (SBCC kit) I added an SBCC proportioning valve in the rear brake line at the time because they would lock on me. Everything was great till this week I noticed while tinkering on the rear and and my wife holding the brake. I had no rear brakes. So I tried to bleed but no fluid at all. Then I opened the proportioning valve all the way and was able to bleed just fine. I pulled the rear drums and adjusted the pads so there was slight drag on the drum when installed. Bled again.. and still no brakes. I didnt seem to be getting any more air. The emergency brake works fine. Could it be they need more adjustment? Or bad cylinders? Possibly bad proportion valve? It did flow fluid freely when all the way open. I left the proportion valve open thinking at least they should lock then decrease as needed. I'm stumped...the fronts work perfectly. Thanks for any advice.