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  #1  
Old 08-14-2019, 10:04 AM
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85 300D power window motor limit

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.
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Old 08-14-2019, 10:52 AM
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Quote:
Originally Posted by funola View Post
Per this post Power window motors, w123 and w126 some power window motors have limit switches built in.
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.
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Old 08-14-2019, 10:56 AM
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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.
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Old 08-14-2019, 11:14 AM
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Sounds like your teeth on your window regulator are worn at the end of its travel.

Last edited by paul roberts; 08-14-2019 at 03:04 PM.
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Old 08-14-2019, 01:32 PM
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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
85 300D power window motor limit-mercedes-300d-window-motor-1.jpg   85 300D power window motor limit-zz-window-regulator-bent-larg-pic.jpg  
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Old 08-14-2019, 09:02 PM
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Quote:
Originally Posted by funola View Post
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?
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.
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Last edited by Graham; 08-16-2019 at 07:29 PM.
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Old 08-14-2019, 09:45 PM
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Quote:
Originally Posted by Graham View Post
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.
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.

Quote:
Originally Posted by Graham View Post
After it cools down, it should reset. But not always!
It appears to me that the switch cycles almost instantly.
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Old 08-14-2019, 10:36 PM
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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.
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Old 08-15-2019, 09:54 AM
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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.
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Old 08-15-2019, 10:12 AM
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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)
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Old 08-15-2019, 10:31 AM
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Quote:
Originally Posted by Graham View Post
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)
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?
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Old 08-15-2019, 10:32 AM
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Quote:
Originally Posted by funola View Post
There's no rust on the bottom support.... it looks pristine.
That's good! This is what my driver front once looked like!

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  #13  
Old 08-15-2019, 10:57 AM
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Post Window Lifts

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 .
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  #14  
Old 08-15-2019, 01:19 PM
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Pristine bottom support
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85 300D power window motor limit-20190809_171847-1305x979.jpg  
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  #15  
Old 08-15-2019, 02:25 PM
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Quote:
Originally Posted by funola View Post
Do you know if the regulator is the same between W123 and W124?
No, I don't know that. EPC search may. But probably some differences in mechanism.
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