Re: 91 F150 brakes
What bleed point are you talking about, the caliper? Make sure the bleeder isn't plugged, just remove it and see if you can get fluid. Check your rubber lines between frame and caliper, the inside liner can collapse causing blockage. Could be blocked in the proportioner as well. Just need to check each section and find where it's blocked.
What bleeding method are you using? 2 man pump and hold? speed bleeders?