Both rear window mechanisms in my recently acquired 1986 300SDL are broken; that stupid white plastic clip (slider) is broken. So I took both mechanisms out of the door.

My question concerns the big spiral spring that assists the mechanism. Is the spring supposed to assist the lifting of the window? Is it supposed to be in a non-tension state when the window is down?

One of my mechanism has the spring assisting in the lifting of the window; the other has very little tension in either direction (this one looks like it may have been changed in the past) the spring is completely "relaxed" in the mid position--halfway up for the window.

I tried preloading the second mechanism by removing the spring and rotating the mechanism 180 degrees. But this puts an incredible amount of preload on the mechanism. I don't think that is right.

Any advice?

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Mike Frederick
1986 300SDL, 240K+ miles
1985 300D KaliKar, 270K+ miles