Depending on the model year, your shimmy might be caused by the shafts not being aligned at the proper alignment marks.

You'll need to check the FSM, but there are machined scribe marks on the drive shafts that will tell you what is balanced. Be forewarned however, that before a specific year, the marks were there but Daimler didn't use them.

They look like this:

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< Rear of car
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So long as that arrow is between the two marks your fine.

__________________
-Typos courtesy of my mobile phone.

yes I know about those marks and my car has them

I think it's cars made before 1982 that don't

I have a rebuilt and balanced driveshaft both flex discs, good engine mounts and good sub-frame mounts

I will loosen up that center nut tomorrow or on thursday because I think I over-tightened it.