External sliding door rollers are worn out.
A handy person from Rockville, MD says:
March 12, 2015
Sliding door panel is 35" X 75.5" X 1.5". It has two sets of two rollers underneath. The rollers are not rolling easily. Do you have new rollers? There are no identifying name or number on the door. It is all vinyl.
Dave from SWISCO responded:
March 17, 2015
We might be able to find something, but I will need more dimensions of the roller itself. I cannot tell what you have based on that tape measurer. Please tell me the width and height of the housing and the diameter of the wheels. That will help us find a good match. In the meantime, you could consider our 81-095 or 81-138, but I cannot guarantee that either will work.