Rear brakes not getting pressure?

[jlwdvm]

I have my Wilwood proportioning valve turned all the way in to get max line pressure to my rear brakes, but I can't seem to be able to get them to lock up. Granted, I have BP30 pads in my Aerolite fronts and BP10 in the FNSL rears. I switched out the 30's I had in the rear because I was getting a weird harmonic vibration sound when rolling to a stop, or moving forward very slowly. The sound went away after the bp10's went in, I can't seem to be able to get the rears to lock up before the fronts on pavement. I know the front pads are much more aggressive, but I thought I could adjust for that with my proportioning valve. I thought the combination would give me the feel I wanted for the street without the increased wear on the rears between track days. Thoughts?