is my proportioning valve bad?? just another brake question

[jmarshall97]

So both my dad and i are having some breaking issues with our square bodies. His is a 1988 r2500 crew and mine a 1986 k20. On my truck when we bleed the rear brakes it just drools out the bleeder, it is quiet honestly pathetic, so i had a looky loo at my proportion valve. I took the rubber cap off and pushed on the button but it didnt budge, i think it may be stuck but how do i know for sure? I havent blead the front breaks yet, but my dads truck is having a similar problem drooling at the back and a fountain at the front and i have a feeling the prop valve is to blame. Any insight would be helpful to the both of us thanks!!