disk brake proportioning valve help

[Custom 68]

ok here is the problem. I did a disk swap on my 68 all new parts from GMC Paul except the master cylinder and prop valve. I got a used prop valve off here. My rear brakes seemed "grabby" (is that a word?) anyway I was never happy with my remufactured master cylinder since it leaked I thought I would start there and replaced it, I bench bled it and installed it. I went to bleed the rears and did that just fine went to the front and no fluid and no brakes I checked the button on the front of the valve and pressed it in while my helper was pushing the brakes that helped but was very intermintent some times it worked and others no fluid. when I had fluid I had lots. after letting it set for a minute or 2 it was back to the same no front brakes...I havent driven it but I am sure it is the same as before.
Do I just need a new prop valve?
thanks
Dave