I'll tell you why I asked if it was friction or viscous: because last time I tried a friction one it made the bike do a slow roll as you were driving along. Kind of like a very long, endless 'S' curve. It would lean over (almost imperceptibly) one way, then the force on the steering would "unstick" the damper which let the steering go over to the other side, at which point it would stick again and the process would then repeat in the other direction. Back and forth endlessly. This happened back in the day on two completely different bikes - a Kawasaki Z1 and a Ducati single.
Has anyone else had that problem?
I can't understand how a friction damper can be of help, on the grounds that if it's loose enough not to cause roll it's too loose to dampen high speed wobbles. (Hence why viscous ones are available, I guess.)
Obviously I must be wrong, though. If anyone can enlighten me I'd be most grateful.