Which came first - chicken or egg...
 

or, which part failed first?

On the 560SEL I just got (the one with the broken flex disk and tailshaft housing damage) I pulled the tunnel cover and drive shaft tonight. As soon as I opened the tunnel, I could see the carrier bearing was toast (rear flex disk is intact) but had no noticeable damage to the surrounding tunnel.

Which is the likelier theory:

The carrier bearing gave out, after plenty of whining, which put added stress on the front flex disk, causing it to fail.

or

The front flex disk was badly worn and causing "clunking", upon failing the carrier bearing was destroyed in the drive shaft melee within the tunnel.

My guess is option one, but I've been known to be wrong before.

I didn't get the tranny number while I was underneath today, will try to remember to next time I'm under there. The number will probably help with my next question. On the tailshaft housing, at approximately 5 o'clock (looking at the tailshaft) there is some type of sensor, attached with a 19mm hollow bolt. What is this sensor?

When I pulled the replacement tailshaft housing, I had the idea to get that sensor as well. Good thing, the one currently installed was hit, and the lead is still attached too, but it has been hit. What should I torque the hollow bolt to?

Thanks all.

This is a 722.323 tranny.

A little research on the transmission site Steve Brotherton provided shows the sensor I asked about, is infact the kickdown solenoid and is torqued to 14 ft/lbs.

Its not a sensor, its the kickdown solenoid. Not sure of the torque for this valve but it has an alluminum sealing washer. Nice and tight so that it dosent leak.

Im not sure of the miles but the front disks often fail before the rear one does. However there is a center pin prodruding from the transmission drive flange that should have held the driveshaft centered even though the disk may have given way. Same at the other end of the drive shaft. I know its that way on both of my 420s. Not sure about yours.

I suspect that both center bearing carrier and the flex disk were in need of replacement and when one went the other could not handle the added stress.