Help diagnosing origin of a transient destabilization?
 

I have a five year old bike with Shimano hydraulic disc brakes. Recently, I have noticed a disconcerting sensation only when braking on fast downhills, where I feel a momentary destabilization, not unlike what you might get with a crosswind. (This happens only when braking on downhills, and during perfectly calm days.) One day while carrying about 10 lbs of stuff in panniers on my rear rack, I noticed that the sensation was much more pronounced.

I've replaced front/rear brake pads, brake rotors, re-bled the rear brake (it needed it anyway), and I have replaced the rear tire after finding a flat spot on it (I thought this was the origin of the problem but now wonder if it was a red herring). However, I am still experiencing this sensation occasionally. I don't hear any brake caliper rub on the discs when braking is not being applied, and no other hints of frame flex or anything like that.

I'm running out of ideas ...

I was getting it some more today on the way home from work. I am pretty sure I saw something flex in the front wheel. It was enough to make me stop and pull the wheel off and inspect stuff. Everything was fine. No play, no binding in the hub. When I got home (having first replaced the wheel), I pulled out the fork and cleaned and re-lubed the headset. The fork (Enve CX, 1st gen) looks absolutely fine, and the headset was fine, despite neglecting it for 5 years. (Chris King's headset is a real work of art. No dirt intrusion in all that time, despite major off-road abuse.)

This is vexing, and I hate getting vexed.

Impressive thread title.

Speed wobble?

Sticky piston?

I don't hear any rubbing when I let off the brakes, so it would have to be really transient. Anyway, I good cleaning of the pistons never hurts. Thanks for the suggestion.

It is kind of like that, but just a single wobble instance.

:twitchy:

I have the answer to your problem, but I don't help banned forum members.

:innocent: