Are the W123 left rear and right rear window regulators interchangeable?

or are they different part numbers?

Also will a W126 rear window regulator work in a W123 rear window?

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72 350SL, 73 450SL, 82 300TD,84 300SD, 85 300D

No (different part #s) and no, sorry.

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83 SD

84 CD

Actually, there was some discussion here recently on using the W126 rear regulators in W123's. They apparently fit, with some minor modifications - mainly swapping a few parts over from your current rear regulator.

The idea is that the W126 regulators are more stout, and don't bend like the rear W123 regulators.

I hope to try this at some point.

I can confirm, though, that window regulators are specific to their side.

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1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!

Using a 126 window regulator on a 123.
W126 Window Regulator into a W123? - Mercedes-Benz Forum

The below is not for everyone. I fixed the Rear passanger side and bought a new one for the drvers side (Regulator Teeth were shot) rear but reinforced both so they would not easily bend again.
At the time the Drivers side rear was $150 each. Now the cost has more than doubled.

The Teeth on the worn Regulator Gear could have been welded up and groudn back in to shape but that would have been extremely time consuming and I did not have any perfect Gear Teeth for a pattern. So I opted to buy a new one.

Extreme Window Regulator Repair
Extreme Rear Window Regulator Repair,123 - PeachParts Mercedes ShopForum

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84 300D, 82 Volvo 244Gl Diesel

Thanks for finding and posting that link. Good info. Next 126 I see at the yard I'll pull the rear regulators and try it.

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1979 300D 040 Black on Black - 1985 300D Maaco job (sadly sprayed over 199 Black Pearl Metallic) on Palamino

http://i.imgur.com/LslW733.jpg

The Baja Arizona Oil Burners Send a message if you'd like to join the fun
Left to Right - UberWasser, Iridium, Stuttgart-->Seattle,, mannys9130

Visit the W123 page on iFixit for over 70 helpful DIY guides!

Also want to mention that the w123 and w126 COUPE front window regulators interchange.

The regulator interchanges, however the glass carriers are different (oddly, the w123 carrier is longer).

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Mac
2002 e320 4matic estate│1985 300d│1980 300td
Previous: 1979 & 1982 & 1983 300sd │ 1982 240d

“Let's take a drive into the middle of nowhere with a packet of Marlboro lights and talk about our lives.” ― Joseph Heller, Catch-22

What kind of nut was used by the OP from the other site? In post#6 of the OP on the other site, the second photo shows a nut. Will this nut come with the shoulder bolt when you order it from McMaster?

W126 Window Regulator into a W123? - Mercedes-Benz Forum

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'85 300D Cal 280,000 miles
'14 GLK 350 60000 miles

It appears he fabricated the "nut" by removing the stud and then drilling and tapping the stud to receive the McMaster shoulder bolt.

Here is a link that shows various photos of the stud that holds the nylon glide in the channel.
http://www.peachparts.com/shopforum/general-information/325520-w123-rear-window-regulator-low-cost-replacement.html

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78 W116 300SD 'Desert Rose' new as of 01/26/2014
79 W116 300SD 'Stormcloud' RIP 04/11/2022

Did this today. It is the second replacement regulator for the rear passenger door. Im hoping it will last a little longer. The regulator was pulled from a 1988 w126 300se.

Attached Thumbnails

     

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'85 300D Cal 280,000 miles
'14 GLK 350 60000 miles

Thanks for sharing this info. I have pulled a pair of W126 regulators, but am not 100% sure what changes I need to make to install:
1. Purchase shoulder bolt from McMaster and use with a standard nut to attach to guide rail (drill out rivet)
2. Change over stops
3. Change over the wiring terminal type? Not sure on this one.

Reach out to ktesler, he sells the w126 regulators for w123 application. I just installed some in my car, but I couldn't tell you the details of all he did.

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Onus probandi incumbit ei qui dicit, non ei qui negat

I recondition w123/w126/w124/w140/r107/r129/ steering boxes!


1984 300D "Elsa" odo reset 6/2011 147k
1983 300TD "Mitzi" ~268k OM603 powered
1995 E300 "Adelheid" 262k [Sold]