[Dashman]

I like Mike B's master cylinder bleeder lines. I was thinking about a tee off the proportioning valve port with a bleeder screw, or straight to a bleeder screw with an adapter (if manufactured), or a tube nut with hard line and vinyl hose. Isn't there a brake line coupler on the frame rail? Maybe you could bleed from there also. I think you're right, it's more likely that you have an air bubble near the start of the rear brake line. Good luck.