either the disk EXTREMELY suddenly failed, or the 124 has SUCH great soundproofing as to mask all but the most serious vibrations... and in my wagon, I hear even the very beginning of a wheelbearing failure...
I'm going to pull and visually inspect my entire driveline once it's in the shop for body repair...

Were there any cracks/indications in the disc at that time?

If you regularly get under the car, cracks are not that bad. Its when you see thread that its time to replace. Just my 2 cents. Lucky! That dampener may be hard to find a replacement.

See thread of what? Threads in the rubber? Threads on a bolt?

I've got something a little lumpy going on underneath and I'm going in for a dive tonight. It seems to be worst in the mornings, engine cold, and haven't been rolling for overnight. After many miles, everything is smooth and stays smooth until next a.m. cold start off to the office. The lumpiness I feel is a rolling lumpiness, almost like cold tires out-of-round due to extremely cold weather. But it's summer, and these are Michelins. Shifting into neutral and coasting makes no difference, still there - I'm pretty sure it's rear of the tranny drive train related. (Could be tranny mount, engine mount, center bearing. I'll be looking at those - again - as well, but were all done within last 2 years).

Just wanted to know more precisely what the first signs of flex disc danger signals.

Like how do these things show signs of wear over time up until they fail? Cracks are obvious to me. What amount of cracking is "change now" versus "ya, they all do that for years", like upper strut mounts.

I've always been taught since I was 11 as soon as you see cracks in the rubber its time to order new ones to replace them...cracks allow the insides to deteriorate in ways you can't see until its too late. Failure can be sudden, and even more destructive than this one was.

That applies to radiator hoses...heater hoses, fan belts, brake hoses and Tires equally.

I think they show in the FSM that the holes will be elongated... in a radial fashion of course.. but I will look again and let you know..

Yes..... what happens in addition to general distortion.. is that the bolts are no longer centered... but you can not see the elongated hole in the rubber because of the size of the washers...but it shows up well because the items they are bolted to are round...
It says If ANY distortion or cracking is found they should be replaced...

Not that I could see, but I didn't pull the transmission mount plate to get a good look.

I see cracks within a month or 2.

By threads I mean strings. There is a guy that makes solid flex disks with urethane bushings to take the stress. Have thought about getting those.

You should check before you try those...
as MB sometimes put either radially soft or tangentally soft flex discs on cars.. 'SOMETIMES mixing them on one car...
it is not likely he has those variations available to match the originals... thus you might set up some kind of vibrations you would not want....

The rubber looked ok on mine when I replaced it - wish I'd taken a pic...but the steel inserts were rattling loose, looked like the rubber there had just disintegrated:eek:

Yes, that is what I was describing ... it goes away under where those inserts are... and you can not see it except that the bolts are then not centered on those inserts...

Exactly, just looking at it, all seemed fine, only grabbing and turning the propshaft showed it was duff. And the slight knocking in and out of gear, obviously:o:o

Must remember to be more... 'proactive' with car problems..seeing what can happen, eh?

cheers!

make sure you also check the rear seal on the trans, when mine let go it took out the rear seal on the trans with it., I think mine was caused by reusing nuts too many times.... I will locktite them when I put it all back together

FYI
 

Bad Flex Disc
http://www.peachparts.com/shopforum/diesel-discussion/121285-bad-flex-disc-post868326.html

Weekend Wrenching (a great picture of a bad flex disc)
http://www.peachparts.com/shopforum/showthread.php?t=216701

The Death of a Flex Disc ... did I kill my 240D?
http://www.peachparts.com/shopforum/diesel-discussion/252017-death-flex-disc-did-i-kill-my-240d-post2194084.html

What happens when you ignore that "little" driveline vibration!
http://www.peachparts.com/shopforum/vintage-mercedes-forum/205055-what-happens-when-you-ignore-little-driveline-vibration.html

Flex Disc Orientation, safety and durability issue.
http://www.peachparts.com/shopforum/tech-help/235575-flex-disc-orientation-safety-durability-issue.html

If your W123 is shaking down the highway. . .
http://www.peachparts.com/shopforum/diesel-discussion/223050-if-your-w123-shaking-down-highway.html

Correct way to install front driveshaft guibo? (FLEX DISC)
http://www.peachparts.com/shopforum/diesel-discussion/187593-correct-way-install-front-driveshaft-guibo.html