Sorry I am late on this post but I have been away from the computer.
As a locksmith I have fixed lots of these over the years.
Several things might be the problem.
First it could be an adjustment. At the bottom of the door about an inch
and a quarter from the bottom there will be a 1/4 inch hole on each edge of
the frame. #2 Phillips clockwise raises the door. The gap should be even
top to bottom when you slide the door open a bit.
Second, the rollers could be not rolling due to carpet fibers cat hair and
general dirt. To clean and inspect them, slide the door open a few inches
and lift. This will allow you to tip the bottom of the door clear and
remove. Upon inspection, if the rollers have run flat you can replace them
for a few bucks at th4e local glass shop or a good hardware store. Bring
the old ones to match them up.
The third thing that could be wrong is that the extrusion that the rollers
ride on has worn beyond the point that you can adjust the rollers. If this
is the case, you can get a U shaped strip at the glass shop for rollers to
If this is a double glazed door and it is wide, the door is going to be
heavy. It is not advisable to repair these on a windy day and a helper can
prevent an expensive oops.
About the time I had mastered getting the toothpaste back in the tube, then
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