My driver side window will go up>down correctly, BUT when going up you have to manully stop its' travel by letting go of the window switch in console. If you do not do this, the window trys to keep closing and makes one hell of a racket .
Question : is there a cut-off switch in this system that opens current to motor when window is at top or bottom of travel ? It goes down and stops correctly; my thinking is that there must be an adjustment on switch or am I totally off base with switch idea ?? Vehicle is a 91 560SEL.

If its a loud clicking noise, mine does that too. The gear teeth in the mechanism are worn out and the assembly will probably need replacement. In the mean time just treat it gently.

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1985 380SE Blue/Blue - 230,000 miles
2012 Subaru Forester 5-speed
2005 Toyota Sienna
2004 Chrysler Sebring convertible
1999 Toyota Tacoma

As far as i know,there is no switch. I replaced both of the gear assemblies [driver and pass. side] but if i keep my finger on the switch it will try to keep going. So i get the window to the top and tap on the button until it is just closed. Poor design!

Since you have replaced both regulators, and did not see a cut-off switch: if a person continues to hold switch down, does this keep current on the motor until switch is relesed ? That would indeed be a very poor design. I guess I will pull door panel off in warm weather and check unit, don't feel like messing with it now.
Now if I could just get the darn radio to work......

I don't think so.But it will put a constant strain on the gear.

I have had my 126 door panels off many times and there is no limit switch and the motor will try to run as long as your finger is on the switch. The design is the same in all the power windows that I have worked on. The designers use "The reasonable person" approach to the design, meaning that a "reasonable person" would not hold the switch any longer than it takes to close the window. From your description I would say that there is a bolt loose on the side of the assembly that is letting the frame flex and disengage making the noise. Might be an easy fix if you do it soon.

Later
Robert

Thanks for input. I will pull panel and check.
have been very careful to not "jam " the window, since the noise indicated a serious problem in my thinking.