I had the same issue once, and it turned out to be my front brake pads. I accidentally got the right and left sides mixed up when I had them off for servicing. As the pads wear, they wear on a slight angle. If you switch their position, it ends up binding in the one caliper and causing it to lock up earlier than the other. It doesn't take much pad wear for this to happen. I would suggest putting a new set of pads on both front calipers and see if your issue goes away.