These tend to come off when opening door too quickly, the drum struggles to keep up throwing the cable off.

Reinstalled mine after looking at the other side which was still attached, your design maybe different though.

Not recommending you do this yourself if uncomfortable with overall operation, it takes some working out as to what does what.

Personally, I hate springs and go to great lengths covering up with safety goggles and so on, this weekend put a new aux belt drive on my 124 - releasing the spring on that stood well to the side lol.

Going back to the door mechanism, mine had no lube on, might go back and grease the wires unless not advised.

__________________
David


1996 Mercedes S124 E300TD - 129k - rolling restoration project -

1998 Mercedes W210 300TD - 118k (assimilated into above vehicle)

If there is only one spring. You are not going to be involved with it. By replacing just one cable on one side.

Basically just loosen the pulley on the side with no wire. Attach the new cable on the bottom of the door fitting. Install the cable end fitting in the pulley and roll the slack out. . Then tighten the pulley bolt. Trying to get the wire as tight as possible with no slack. Ideally the tension should seem about the same as the other side.

If this is not achieved just raise the door a little and put a brick under the same side. Loosen the pulley again and take up a little slop in the wire. As long as you are not playing around with the spring in any way and there is only one. It should go safe and easy.

On the other hand if you have any self doubts a door guy can do it pretty fast. Maybe check with a few for prices as this is also a deal where many doing it are scammers.

Check the cable that broke for rust. If any do a visual inspection of the other one in place. After you or the door guy get finished. Rubbing a little grease into the wires will probably extend their service life.

Yes I have installed much heavier roll up doors. With very strong springs in comparison to domestic garage doors. You are not installing a door with the risks involved. By Just replacing a cable. The bolt that locks the wire pulley to the main shaft should be pretty tight. It could also have slipped a little causing this.