I think one has to be careful in assuming that preload on steering head bearings is the answer to the wobble. ...
Ditto. I get a 40-20 MPH decel wobble (hands off) with
some tire combinations. Steering stem preload can be a factor, but over torquing it can cause more problems. Dented races, or wandering on a straight road are but two examples. Neither are pretty, the latter leads to the former, and the former can be a PITA to repair.
A clunk over bumps can be from several things. Most often it's a [minor] slop in the fork bushings. You can recreate the clunk by flipping the front brake on a straight/smooth surface. "chattering" the front brake as you come to a stop, if you will. Sometimes it can be eliminated by replacing the fork bushings. But if the slider body is worn, no amount of replacing bushings will fix. Some have shimmed the bushings (.001" -
shim stock), but these shim jobs typically cold creep, or blow out, after a few miles.
Loose brake pads may be a cause also. No real fix for this. You can narrow it down by rapping the front tire/wheel assembly 'briskly' while it's on the centerstand, and the front wheel is off the ground. A judicious swing of a stout two by four may be called for.
My two Centavos...
Rick