Nissan Repair: sentra brake, flare nut, proportioning valve

Question
hello,i'm back. 92 sentra xe, The problem is figuring out why
front cailpers are locking up gradually, over a little time.
new rotors, one caliper, other was near new, new master cylinder, pads +shoes. master cylinder and brakes were bled a couple of
times , i have done this before, so i feel like the air is out of the system( i've been wrong before too).
  Any chance the proportioning valve could be causing a problem?
I can drive 5 miles use the brakes normally, and after a time
the pedal gets higher and higher and i can feel the drag. Found i could tap each of the front bleed screws a tad- with a rag - and lower the pedal and release the brakes( and get home). also, rotors were not turned- back brakes seem fine.   thanks much,
         jon

Answer
Hi Jon -

Yes, could be proportioning valve, however try checking the brake switch adjustment first. If the switch is not at the correct position, the pedal will not return all the way up, so the brakes will be "applied" while driving, getting worse as the system heats up.

Otherwise, next time it starts dragging, loosen the flare nut before and after the proportioning valve to narrow down where it is hung up.

Might have to do this several times to figure it out.

Hope this helps -
aloha
calvin