Front brakes caliper piston sticking
 

I switched out the two front calipers since the old ones were dragging and had 150k miles on them. only problem is the new ones are dragging too. i noticed that the caliper pistons are NOT retracting / pulling back in when i let go of the brakes so they keep braking / pushing the pads on the disc. to get them to retract i have to open up the bleed screw and push the piston back in. but after 1~2 miles of driving and breaking the brakes start rubbing again, and when i check them, the piston is still sticking out and pushing the pads against the disc.

what pulls the caliper piston back in one you finish breaking? how can i fix this?

thanks in advance!

RE: Front brakes caliper piston sticking
 

Porportioning valve...

RE: Front brakes caliper piston sticking
 

turns out the brake light switch had come a little loose (i have no idea how) and wasn't allowing the brake pedal to go back 1/8 of an inch.
guess that 1/8 of an inch mattered because once i tightened the switch in proper place, and allowed the brake pedal to return all the way back, brakes worked fine.
guess i got new calipers for no real reason... oh well :]

thanks everyone for your input!!