Proportioning Valve Keeps Tripping?

[KyleSeal]

This weekend I tried the power bleeder. No dice.

I am beginning to believe I am pulling air, but not leaking fluid. I have heard numerous times now about wheel cylinders bringing mystery air in. These wheel cylinders are probably 8 years old, never used. That being said, I never had fluid in the system to test them. I am going to replace them and recheck.

Everytime I go to bleed the rears, I get micro bubbles and sometimes very small ones, but regardless I get a stream every time I open the bleeder. I ran nearly a gallon of fluid through them and still had the same situation.

I also rebled the master cylinder to ensure no air is trapped in it, and it bled clean.