Bearing Hub

Most front-wheel-drive vehicles have a split-diagonal hydraulic system so the left rear and right front are on the same system. If only one rear brake is worn, check the opposite front one. If just that one is worn too, suspect a master cylinder problem, but that's more of a GM thing. To check for a restriction, try pedal bleeding at one of the wheels where the linings are not worn. If no fluid comes out, suspect a valve has tripped in the master cylinder, (again, that's more of a GM problem), or the brake fluid is contaminated with petroleum product. That will cause the rubber lip seals in the master cylinder to swell and grow past the fluid return ports blocking them off.