Have you checked the cable to each wheel. Disconnect at both ends and check for free movement. There should not be any significant drag or binding. If the outer jacket is damaged or shows any sign of bulging the cable is shot. The spring on each cable end is responsible to push the lever back and properly adjusted should just come free of the push bar, (adjuster). The pivot bar that attaches to the front cable should pivot so both sides equalize as brake is set and then allow both sides to fully release. The nut is a special nut with a ball seat. There should not be a regular nut or washer at the pivot lever.

Dennis