Rear window won't go all the way up on 123 sedan
 

The passenger side rear window on my 300SD stops about 4-5mm short of going all the way up. When it reaches that level the motor keeps going, but the window just lurches up and down ever so slightly. I can pull it the rest of the way up and it will stay there.

When I try to roll it down from its 4-5mm peak, it won't go down unless it's a hot day, in which case it will usually work. If I have pulled it all the way up, it won't go down at all.

It seems like a gear issue. I have had the door panel off and I don't see any adjustments other than the stop for when it's all the way down.

Where should I go from here?

Since you have had the door panel off you know how to get in there.

I do not have a specific answer for that exact problem.

But I would recommend that you remove the entire regulator assembly and
get it out where you can study it.

Things are much better repaired before complete failure.

Three 10mm head bolts hold the regulator to the door.

If I remember right I disconnected the window from the regulator mechanism,
then used the switch to bring the regulator down, get it out from the door.

If you want to prop the window up with a length of PVC or wood stick
cut to size it will hold the window up quite nicely until you are ready to
reinsert the regulator.

Now, with the regulator out you can easily check for it being bent,
missing tooth, and check the plastic sliding piece that the bottom
of the window connects to, these do get replaced and are readily
available, cheaply.

In all the years and all the window problems I have only replaced a regulator once or twice. A motor - never.

Hope this helped.

From your description it sounds like the teeth on the regulator gear are worn. Fairly common for the teeth on the end of that gear to get worn down from folks keeping that switch depressed just a little to long and over the years the teeth just get chewed away. If this is the case you'll have to replace the regulator.

The Regulator Frame that is made of something like the Metal Carburetors are made from bends.

The Gear teeth on the Motor are extremely Hard and begin to eat up the Regulator Gear Teeth that are soft compared to the Motor Gear.
Also at the time I posted the below thread a rear Window Regulator was about $150 something. Since than the price has go up a lot.

I replace one because I believed the Teeth were too bad on it. I suppose the Teeth could have been welded and ground or filed back into shape but that was too much work for me.

Extreme Window Regulator Repair
http://www.peachparts.com/shopforum/showthread.php?t=254722&highlight=Extreme