1986 420 SEL Window problem
 

The driver's window in my 420 SEL rumbles on the way up and doesn't close completely. Before I tear the door apart I'm wondering if anyone knows the specific problem and what I'll need to fix it when I get in there. Thanks, mark

Could be a bent regulator, or a broken slide (attaches to regulator and slides in a C channel), or stripped gears on either regulator or motor.

The slide isn't hard to replace, just time consuming - patience)
The regulator is expensive new - if you don't want new, junk yard is an option.
Same for the motor.
Both regulator and motor can be found on ebay - count the teeth on the motor and verify brand/manufacturer.

I'm guessing your regulator is bent a little. All the moving parts have lost their grease and don't move as easy as when new causing the regulator to get too much torque on it. Easy to get to and replace or fix. If you do, there are threads here to help with removal of door panel. I have not had to do it with my W126 but I know on the W123's I have done, there is a trick to getting the map pocket off.

420 Sel
 

Thanks for the help. It sounds like I need to get it apart before it'll be clear what I need. How do I find the thread on getting the door panel off? Thanks, Mark

Try this one:
http://www.peachparts.com/shopforum/showthread.php?t=150747&highlight=w126+door+panel

If that doesn't help, just use the search function (upper right) in tech help. Type in something like: W126 door panel or something of that nature.

It's not really all that hard to take off the inside door cladding.
Just don't be in a hurry. Get a little bowl or something to put all the little screws into. If you get stuck, take a pic and post it.

420 Sel
 

Thank You all for the help. Mark

I'd bet on the sliding jaw, has been mentioned a few times. Once in awhile the screws will loosen up or fall off which acts kind of like this too.
Gilly

Now the fun part
 

I got the works out and the gear on the motor is stripped as are the teeth on the c-shaped arm of the regulator - looks like I need both. Do you all know whether the motor and regulator are the same on all windows or are they unique to the driver's side? Thanks, Mark

Oops.
 

Sorry guys. It didn't take long looking at ebay to realize that each window is different and there are a million of these. Thanks for all the help. I'll find one somewhere. Thanks, Mark

My book shows 2 different manufacturers, and none of the parts interchange, regulator and motor both. Of course my parts car had the "wrong" brand when I needed a regulator for my 420SEL?!