Make sure the bottom is riding on the wheels. Sometimes the wheels can come off the rail and it's riding on the door frame of the glass instead.
CAPS LOCK
Packing grease or pb blaster on the track and open an close the door a few times to get it worked in real good an make sure to spread it all along the track
Rub candle wax into the runners on the track. It will help lubricate the channel without causing corrosion
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