W123 rear window, strange problem

[H-townbenzoboy]

Well, today, I was putting up the rear driver's side window on the 300D, and when the window got to the fully closed position, instead of the motor going off if you leave your finger on the switch too long, it would keep trying to go up, kind of bounce up and down if you can say. I don't use the rear windows much, but what would cause the window to do that?
-Joe

[Johnhef]

There might be a tooth or two missing from that point in the regulator. The 83 coupe I aquired has the same problem, I need to get a regulator for it so the window will stay closed on its own.

My passenger front window does this as well. Its a missing tooth/section on the plastic gear inside the worm gear drive off the motor. Consider your window limping...unforntunately it can only get worse from here

I just play it easy on my window and not let it keep "trying to go" once it gets to the top and making that "pop, pop, pop" sound..
Also this applies to the bottom.

Until you can find a worm drive...take it easy

[Brian Carlton]

Yes, this issue is common. And it is caused by:

Originally Posted by H-townbenzoboy

............you leave your finger on the switch too long..........

The motor doesn't have a limit switch, so the worm gear on the regulator perfoms that function for you.

[herbct01]

I had the same problem with my '80 300D. At first the window would slip down a little while driving and do what you described when raised.
I pulled the door panel and found the teeth at the end of the window regulator worn. I checked my spare Benz in the woods and found that was also the case with that one. Strangely, this is the only reuglator that showed this type of wear.
I priced the part and it was over $100 so to the bone yard I go. It took a bit of searching to find a left rear regulator that was not worn in the same manner. I did find one with a little wear for $12, installed it and now no more "dropping" window. Since the wear is on this one also I still get the strange noise you describe. I'm just careful to release the button after the firts bump.
I hope this helps.

[ridinsmooth]

Mine "bumps" all the way up or down. Fortunately it stays up on it's own, and since I never really have backseat passengers to want it down, I haven't worried about it too much. Just another little item on the "to do when I win the lottery" list.

[dmorrison]

Heres a post with a picture of the rear regulators out of my daughters 240D. they sometimes warp and the gears loose there mesh.

Scroll down to the bottom.

http://www.peachparts.com/shopforum/showthread.php?t=110753&highlight=warped+regulator+dave


Dave