Hello! Going through my new 1980 300CD. I looks like someone tried to put in a manual crank regulator out of a 4 door, so i removed it and found a proper power one.

I tested it out of the car - strong, gears are all good, smooth, etc. I lube everything and put it in, get everything adjusted, but it's doing something strange. When the window is 80% up, it will clunk, the window will fall 3 inches, then continue up and repeat. If I help it past that little bit, it's fine. There isn't any resistance I can detect right then, unless its in the rubber channels...

Any ideas?

Thanks-
-rj

I'm not familiar with the regulators for the coupe, but the back window regulators from the sedan are prone to flexing (probably the front as well). You might check to see that everything is in the same plane. I ended up using some C Clamps to clamp one of my back regulators to a chunk of 2x12 and pull it back mostly in line.

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'85 300D - federal spec, built in late 84. 85 300D Complete AC System Rebuild