If you roll your passenger side window all the way down, does it make it all the way up? I can roll mine down no more than a couple of inches - any more than that causes it to slow to a crawl. No way it can make it all the way from the bottom to the top.

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2003 X5 4.4i
1992 Porsche 968
2007 328i
2014 Subaru Forester XT