I have wilwood front disc that cam on my car they are 4 piston. the master looks to be aftermarket. I have rear drums. the problem Iam haveing is sometimes only one front brake seems to work and some times the backs lock up. there is no portioning valve as there wasnt one when I got the car. So do I need one? if so should I get after market or a vette or firebird or other gm product one. also if I get after market how do I adjust it?

Wilwood makes a very nice adjustable proportioning valve for $80-85. We use one on our circle track car. It has detents that make adjusting and holding adjustment easy. I am looking at SSBC's Adjustable Prop Valve on my 72 w/Kore 3 Z51 frt brakes and Wilwood 4 piston Rears but can only verify how well the Wilwood knob style prop valve works. As far as adjusting the prop valve we used an infared therm gun but before that we would lock front brakes up and turn 2 clicks to rear.