Proportioning Valve Problems

Today I replaced the rear brake hose and PROBLEM SOLVED. The hose on the car(which was replaced around 2005) was blocked. Upon removal I was just able to get air to go through it. After repeatedly trying to clear the line with compressed air eventually no air would pass through it. It definitely had to go. I don't drive the car near enough and it stays outside all the time. I think the combination of inactivity and moisture took its toll on it. I wonder if I cooked the springs enough to lose their temper? Anyway, thanks everyone for your advice.