Got it fixed! I was able to get the rear sway bars local. I really have to plug Foreign Parts Specialists, they had it in stock for 15$ and they are within a mile of the house.

When I pulled the rear tire off it was pretty obvious what the clunk, and shimmy were as the wheel spacer had split right where the hub centric portion meets the body of the spacer I've got the 15 inch wheels on it now and I will never be running wheel spacers again. I'm a little surprised though as those were the billet spacers made for this model vehicle, and the rims they went on were also Mercedes rims, they seemed to fit really well.

My best hypothesis is that I had two things wrong at the same time on both ends of the car with very similar symptoms. The original vibration was the old rubber bits on the front end of the car, but at some point prior to me replacing those parts one of the rear wheel spacers had split, causing a similar shimmy at the same speed. Very weird.

Anyways the shimmy is gone, so I took out for a test run at highway speeds and the car seemed very happy, my 5 minute test run ended up about 20 minutes though because it was nice to have it running again. Thanks for the help everybody!

Yep, spacers are generally a risky proposition. Unless they are very costly and manufactured with .0005" runout, they're going to cause problems.

I wish I had noticed that tidbit in the first post.

It seems like your shake or shimmy is coming from the front end of your car. I would start looking really close at all rotating components in the front end.

It seems like you have already touched all of the suspension in the front end, which narrows it down to rotating running gear. Do you know when the last time the front wheel bearings were replaced? front brake rotors?

Beyond that I am running out of tire speed rotating devices to suggest checking to try and find this wiggle.

It is interesting that the 16" wheels fix the problem I think that you might be right with it masks the wiggle with its shear size and weight. with that being the case it looks like it is either your 15" wheels or something chassis related.

Keep us posted on any new findings.

__________________
'81 300D - swapped to a 617.951 turbo motor with a 150 amp alt.

Ditto that would have been useful info. I tried a variety of combos before I just came to the realization they are always a bad idea.

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