'69 brake distribution valve function

[Verne_Frantz]

I asked this question on the Chevelle site but no answers yet. My ELC has drum-drum brakes and I can't seem to get the rears bled properly. There is almost no flow of fluid. The system is all stock with a rebuilt master and new wheel cylinders. My question is: does that valve partially close off the front or rear if there is a leak or an open line? I've looked at the pin inside that is under the switch and all I see is a straight smooth pin. I don't see anything that would cause it to activate the switch. I want to know if that valve could be my problem or if I should look elsewhere.

thanks
Verne