Hoping someone can shed some light on a brake problem that just occurred on my 2003 F150. The right front brake suddenly quit working and the truck pulls hard left when brakes are applied. I pulled the caliper and it appears to be ok, replaced the lower brake line going into the caliper and tried to bleed the brakes but nothing comes out the upper brake line going to the master cylinder. Could it just be some blockage in the line, a faulty master cylinder affecting only one side, or what? Thanks for any help.