The car: 1981 240D Manual

The symptom: A week or so as I was driving along a loud bang as something flew into the drive tunnel. No symptoms for a few days, but now about halfway through first and second gear, a tapping/knocking sound and vibration comes from the bottom of the car, right from the transmission tunnel. You can feel the thunk,thunk,thunk through the driver's seat. Its bad. once revs get high, the vibration, knock, thump goes away - usually by the middle of third gear.

This is obviously a driveline problem, and it developed quickly - over three or four days to the point that it is now loud enough that I have parked the car for fear of what it will do when this lets go.

I am going through the list of what this could be. Universal joint? Flex disc? bearing? Motor mount? What else is there between the engine and the rear end?

When I replaced the oil pan a few weeks ago I noticed that the motor mount it rests against was badly boogered and needed replacing. As its a $11 part, I'll replace it for sure. The car is now at the local wrenchtwister's (baby its cold outside - I'm not equipped to roll around on cold asphalt). Any ideas are appreciated.

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1981 240 D in the Toronto Area
Ivory with one black fender