Bad proportioning valve?

[stss96]

I was having trouble holding boost on the line. I installed s-10 wheels cylinders and 4 long shoes. I still can't hold any boost. Is it possible I have a bad proporting valve? How far is the little nip on the end suppose to be sticking out?? I looks like its out some I tried pushing it back in but it wouldn't budge. Could it be frozen???