W124 Window Regulator Replacement
 

Was taking dogs to the vet for shots today and forgot about the sticky drivers rear window. Rolled it down for them to hang their heads out, but when I went to roll it up I heard a click from there and it wouldn't move.


Got home, got the panel off and the problem was obvious, there was a loose cable hanging with a spring on the end of it. Another plastic Mercedes part that is not up the the duty it is subjected to had broken. Luckily, I had a good regulator in the parts car, and replacement was a 10 minute fix.


Remove the door panel.


Roll the window halfway down, remove motor wires from terminal block and pass through the inner door skin.


There is a plastic block that lifts the window. It rides in a short track with a plastic lock clip. Push the tip of the clip towards the plastic block on each end and it drops out downwards.


Remove three motor screws and two rail screws.


Push the motor back until the screws clear the inner door skin. Slide the rail up just a few mm to release the clip under the bolt hole. Slide the rail aft slightly to disengage the lift block from the window slide. Push window fully closed.


Tilt top of the regulator towards the rear end of the door. Tilt the motor out and pull the entire regulator system out.


Reverse to install new one.


Also, word to the wise... only roll the window up until it is fully closed. Don't lay on the switch after it stops. Running to the stop pulls the spring tensioners in the cable to the stop, which puts a heavy load on the plastic lift mechanism. Slamming the door or riding a bumpy road with the regulator system bound up tight like that is like beating on the plastic lift part with a hammer.

The plastic piece is called the sliding jaw. It is designed to break when the regulator arm gets too much tension. I have replaced about five of them in my '81 300SD over some 35+ years. I just bought a new type sliding jaw made by a forum member Diseasel300; will report back as soon as I install it.

The problem with the original sliding jaw is that you have to drill out a rivet which holds it in place. The new one does not have a rivet.

I was lucky enough to have an entire working regulator and motor in the parts car, so same day fix. I saved the old one to look at rebuilding it. Being a machinist, I can whittle a new part out of aluminum pretty easily, if the need should arise.