My buddy got a 1985 300D turbodiesel so I'll be posting on this forum too.

The drivers side rear seat window goes up and down, not very smoothly with a machine gun like sound. When at the top it continues to make that same sound.

So what is broken and needs to be fixed or replaced?

Sounds like a stripped gear on the motor/lifter drive assembly....allowing the motor to keep turning (and skipping) when it reaches the top and while its moving. I'd think if you keep using it that gear is going to get so stripped that its not going to move at all So I'd fix that promptly....

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

I second his assessment.............

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
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"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

Is that gear accessible with the window up or down?

If it's a pain to get to I'll just tell him not to use that window. The A/C works great so it should not be an inconvience since it's a rear window.

The assembly can be somewhat of a pain to work on, but there's enough room to get to it...personally I'd fix it just in case it ever got put down by accident, and then couldn't be raised again....for now I'd agree its a good idea to just not use the window.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

its part of the window regulator assembly..............you have to replace the regualtor................pull the panel and you will see..............

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche

I took the panel off to change the door check strap and I could see the regulator and all. I'll just not reconnect the wires to the rear window switch and disconnect the connector from the one on the console panel for now, so he'll not put it down by mistake and not be able to put it up.

So I would need to put a different regulator in there? I can't get another gear and replace it? I saw a regulator kit on Fastlanes website but I couldn't tell if it had the gear in question.

Edited: If I disconnect the switch in the rear will I still have to disconnect the one in the console, I'm thinking maybe not?

That regulator kit is for the other end of the arm the gear is on..........its not going to fix the problem you have.....only cure is a new regulator.

__________________
Proud owner of ....
1971 280SE W108
1979 300SD W116
1983 300D W123
1975 Ironhead Sportster chopper
1987 GMC 3/4 ton 4X4 Diesel
1989 Honda Civic (Heavily modified)
---------------------
Section 609 MVAC Certified
---------------------
"He who fights with monsters might take care lest he thereby become a monster. And if you gaze for long into an abyss, the abyss gazes also into you." - Friedrich Nietzsche