The Vincent streamliner eliminated bump steering in this manner: (this wasn't my idea, it was an idea of Don Vesco's.) Don utilized the system on his liners and actually gave a system to Bob George (builder of the Easy Rider) It's simple.
Mount your pivot arm solid to the forward bulkhead in a double bearing cage. Hang a U joint on the pivot arm shaft, then make solid to the end of the U joint a female spline, then a male spline. Try to make the spline fit well. Then affix a U joint to the male spline. Affix solid another bearing cage to the front swing arm, the same cage bearing set up. This is your bottom pivot arm, then the drag link from your bottom pivot arm to the center hub steering. Grab the handlebars and you can bounce it all you want. You have eliminated the hard connection between the two things that cause bump steering, the handlebars, solidly mounted in a pivot bearing set up, and the center hub, which is solidly mounted in a pivot bearing king pin set up. Now what you have is the swing arm going up and down, but the floating splines eliminate the physics involved with fixed points.
Max
