Brakes/proportioning valve

[W350Eddie]

I recently replaced my rear brakes, emergency brake cables, lines from the master cylinder to the proportioning valve, and bled the brakes. I'm having a pulling to the left (sometimes) and a pull to the right sometimes when i apply about a medium amount of brakes. Now i know I'm going to re-bleed the brakes again, but is it common to have it pull to either side at different times or is there something wrong with my proportioning valve?

[simplysmn]

you may have a dragging brake caliper on the front

[Ol_blue88]

usually if something is going on with your proportioning valve the sensor located on top of the valve will detect the valve is off center and cause your parking brake light to stay on