Firstfives.org

So I finally got around to sorting out the problem with falling glass in my rear driver side door. I put in a new regulator and used the old motor. When I got it all back together, it moves very slowly and I feel like the motor is being strained. It moved quickly until I got the piece that holds the bottom of the glass re-attached to the vertical runner, so I think that is giving too much friction. I cleaned off most of the old thick black grease and sprayed it with silicone, but it is still super slow. My main objective was to get it so the window would stay up, but after putting time and money into it it would be nice to have a window I can actually use without worrying about killing the motor! Any tips before I put the door card back on would be greatly appreciated! Thanks -Matty in Minneapolis

With the panel off the assignment is patient cleaning, lubricating and adjusting. Continue that process, testing with the switch, until the window works as factory new.

Clean out the bottom of the door, drain holes, for any rust, crud. Place a towel there to lessen the rust, dripping, penetrating oil spray used to get all of the parts working smoothly. Compressed air works well, with WD40, plain oil final. Read the tech adjustment steps or use your own observations the glass is set in the frame properly to be traveling up and down smoothly in the track.

Yes, you may have to check, re glue the glass into the black tape inside the metal frame brackets.

https://www.bmwtechinfo.com/repair/main/057en/index.htm