No, balancing is not needed, at least not so no vibration will be felt. I am not saying that they do not need to be balanced as per recommendations, just that you can get by without (4 conversions and going strong) it.

Try moving the rear tranny mount diagonally, also remember that the 240Ds did not have provision for the engine shocks so some vibration will be felt (or did I read wrong, is it a 4-speed into a 300D chassis ??)

The other , more likely, possibility is that the driveshaft half was put back in grossly misaligned (like almost 180 deg apart)

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1982 300SD (214 k, excellent shape) kidmobile running mostly biodiesel, gets 31 mpg hwy with 2.82 rear from a euro 500SEL



1976 115 body 240D 4-speed (traded for Jeep parts) - Engine lives on in my CJ7