It happened to me a few times in a Citabria, until an engineer advised me to get the tyre pressure spot on. This can be a fiddly job with such a small inner tube. There was no further shimmy with the correct tyre pressure.
I never had shimmy in a 185, but I did have the nut come undone, resulting in the tail wheel falling off. There wasn't much damage as I wheeled it on at Lae, and vacated very slowly on the "skid".
Cilba