Jack a rear wheel free of the ground and apply a wrench to a lug bolt with the parking brake applied(be careful not to knock the car off the jack!). If the wheel moves forward and back under torque on the lug bolts, replace torque and thrust links in the rear suspension. Bad torque links cause sloppy handling and serious thumps and bangs back there, including on shifts.

Otherwise, inspect the vacuum line to the transmission. A bad vac line (or other cuase of a vac leak such as bad idle control valve hoses, etc) will cause hard shifts. I'd bet, if the rear suspension is OK and you don't have a bad flex disk, you have a bad vac line.

Check the flex disk, the front one only seems to last about 60,000 miles.

you should also check the differential mounts. They are on the rear subframe behind the diff, steel insert must be centered and not move much when the diff is jacked up. Bad ones cause a knock.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!