My garage door no longer closes smoothly. When I manually close the door,
the force needed varies from almost none to quite a hefty pull. When the
garage door opener closes the door, the whole thing bucks and shakes. I've
lubricated the tracks, wheels and axels with no luck. The door is not
warped and the tracks are not bent or buckled. When the door is full open,
the springs sag about the same amount, so I'm assuming that the tension is
about the same in both springs. It seems to hang up when the wheels are on
either side of the bend in the track.

Any ideas?