need help with bleeding brakes

[wlf89]

i replaced both rear wheel cylinder on a 87r10 today along with new pads, the truck has been sitting for along time. i filled the master with fluid and cracked the bleeders and i am getting good fluid flow with gravity. after this i cranked it up and pumped and held pedal while opening the bleeders with a helper, and i got very little fluid and the pedal doesnt go down at all like it should.

is this a proportioning valve issue? ive heard of people resetting them but ive never had to do this and not sure how to go about it. a video i watched said if your not getting fluid to the rear to just pump and hold pedal and bleed the front 2-3 times and that should reset the valve, is that true or is it done some other way? thanks for the help