Technical straight axle front end shimmy

I have a '32 beam axle Ford roadster that has a strong front end shimmy at about 70 MPH. It had this once before and I put a SoCal damper on it and it was fine for several years. First time out this year it started again. I couldn't find anything obvious so I put a new damper on with no success. I have the straight tread tractor looking tires on the front. The wheel bearings seem OK. Anyone have any thoughts? Bob

 

Tires could be seperating

 

How much caster are you running?

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Had this problem with a Jeep that sat up all winter. Tires apparently got out of round.
New tires and a balance job solved the problem completely.

 

Search death wobble on here and start reading.....its all been said....but im with the above poster - if you changed nothing between when you last drove it and now, its probably the tires.....they gave me a fit when I had my willys.....switching to the pro tracs solved my problem