pifcat2, use a box-end wrench on the nuts/bolts facing the differential. An open end wrench is likely to cause the problems you're having. Try bracing the box-end wrench and turn the socket/breaker bar setup to loosen the nuts/bolts. For the driveshaft halves to separate you'll need 41mm and 43mm open-end wrenches to loosen the nut at the slip joint. I replaced the rear flex disc on our 1992 300CE last year and the nuts/bolts were fairly easy to remove after the first half-turn.

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Fred Hoelzle