My left front brake keeps locking up when it does I bleed that side and it will

yes I did clean and grease the pins.I replaced pad on both sides.It started locking up before I replaced everthing but only on the left front wheel,so I changed out that clapler and had rotors turned and replaced pads,but It dodn't help.It did it the other day I pulled over and and opened the bleeder on that wheel and it released I then drove it all day ran around 200 miles with no problem next day it locked up again.would a bad speed sensor cause this problem or something with my abs?