Per this post Power window motors, w123 and w126 some power window motors have limit switches built in. Does 85 300D's have this kind of motor?

On my 85 all windows except driver's rear go up and down quietly. When topped/ bottomed out, makes no additional noise.

On the driver's rear window, it goes down and bottoms out quietly. But on the way up, it sounds different than the other windows where it ratchets. The ratcheting gets louder if I hold the switch after it tops out. Anyone know what's wrong?

This is one of the last item on this car that I have not looked into since the rear window is seldom used. I'd like to address it now.

Any info appreciated.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Those are not "limit switches" by my definition. More of a momentary circuit breaker which serves a comparable function. In any case, I am betting that a 1985 model 300D would be so equipped.

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

Probably the bent frame issue that has been reported here before (no limit switches on my 85). I have a similar issue but on the Rear Passenger side. Some users have done straightening and reinforcements of the frames. There are posts on the DIY.

__________________
1985 300D
The rest:
1957 MGA (comatose)
1965 Falcon (sleeping)
1966 E-100 (rust test in progress)
1976 Ford 3400 D Tractor (workhorse)
1978 Mercury Zephyer (5L playtoy)
1995 Isuzu NPR D (fetcher)
1998 Subaru Legacy (Spare)
2000 Toyota Sienna (School bus)
2008 Toyota Prius (Commuter)

Sounds like your teeth on your window regulator are worn at the end of its travel.

When the pot metal frame bends the teeth on the regulator start to wear badly. The Motor Gear is much harder then the regulator teeth.

I replaced one with a new regulator but at that time they were $150 but several years ago they were $360.

It might be that by this time URO or some other aftermarket company makes them.

Extreme Window Regulator Repair
Extreme Rear Window Regulator Repair,123 - PeachParts Mercedes-Benz Forum

The thing with the contact points that breaks the circuit where the yellow arrow points.
Dorman makes front window regulators for W123's they may also have started making the rear ones.
In the next pic you can see the bend and with a closer look can see the tooth wear.

Attached Thumbnails

   

__________________
84 300D, 82 Volvo 244Gl Diesel

The '85 300D and probably most benzes of that era don't exactly have a limit switch. What they have, is a thermal overload switch. If the button is held down too long or if there is excessive friction in the mechanism or window, then this switch can trip. After it cools down, it should reset. But not always!

The switch is actually an integral part of the motor. If you do a search, you should find a long discussion about these switches.

Sounds like it is time to pull your window lifter. Make sure the metal edge at the bottom of the glass has not rusted out and is catching on way up (I had that on front window and I think posted about it). Could also be the gears.

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5

In my experience, the switch opens almost concurrently with the window reaching the extreme limits of its travel. When raising the window, for example, you can hear the motor stop within a fraction of a second of the window stopping in the UP position. Subsequent depressions of the switch on th UP side will result in the motor attempting to run for a fraction of a second, then stopping.

It appears to me that the switch cycles almost instantly.

__________________
When cryptography is outlawed, bayl bhgynjf jvyy unir cevinpl.

At least on coupe W123 cars have a 90 degree piece of metal that has a rubber coating on it where the regulator hits.

I’ve had a car where the piece, which is bolted into place but can be adjusted, flipped the wrong way, yet had enough adjustment that it almost stopped in the right place but was a bit off.

I have to wonder if a stop is not correctly adjusted and the rubber piece is grabbing and then the torque is making the mechanism jump.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Thanks for the info so far. I have not had time to do much with it other than take the panel off. There's no rust on the bottom support.... it looks pristine. Maybe I'll look with a mirror as I work the window switch and see if I can tell what's going on first. Next step is take the regulator/ motor out.

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Doesn't sound like your problem, but here are the links where we discussed the Otter thermal overload switch that is internal to the motor as well as other issues:

W123 300D Window won't open

W123 300D Window won't open

Repair your failed W124 window regulator motor (and maybe others too)

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5

Good info to have, thanks! I know the motor is the same for quite a few different Mercedes models from 84-95 https://parts.jackingrammercedes.com/oem-parts/mercedes-benz-window-motor-0028208542?c=Zz1lbGVjdHJpY2FsJnM9ZnJvbnQtZG9vciZsPTEmbj1Bc3NlbWJsaWVzIFBhZ2UmYT1tZXJjZWRlcy1iZW56Jm8 9MzAwc2RsJnk9MTk4NiZ0PWJhc2UmZT0zLTBsLWw2LWRpZXNlbA%3D%3D

Do you know if the regulator is the same between W123 and W124?

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

That's good! This is what my driver front once looked like!

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5

The thermal breaker doesn't stop the electric motor from bending the crap out of the life mechanism if the button is held too long, I've replaced quite a few lifts, almost always in cars with children or stupids who think deliberately breaking things is good .

Don't waste any time straightening bent lifts, they'll bend again ere long .

If you use used (junkyard etc.) window lifts, BE SURE to count the teeth on the lift motor as there's two different tooth counts ! .

Often I can $ave 50 % on a junkyard lift by not buying the electric motor, those rarely need replacing yet are the first in demand .

__________________
-Nate
1982 240D 408,XXX miles
Ignorance is the mother of suspicion and fear is the father

I did then what I knew how to do ~ now that I know better I do better

Pristine bottom support

Attached Thumbnails

 

__________________
85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

No, I don't know that. EPC search may. But probably some differences in mechanism.

__________________
Graham
85 300D,72 350SL, 98 E320, Outback 2.5