On 2/9/2019 4:34 PM, jbeattie wrote:

Rule of thumb -- when you have a BB noise, start with the rear axle drop-out interface. I ignored the rule of thumb trying to track down what was clearly (in my mind) a BB problem -- a light thunk every time the left pedal arm hit the bottom of the stroke. This was on my Synapse with an OE Cannondale SI crank -- a pretty simple crank with a SRAM-like interface (bolt on arm and not pinch bolts like Shimano). So, I get out my jumbo 10mm hex socket to remove the bolt/cap, pull of the crank with a kludged Park remover (long story), check the bearings -- and they're fine. Grease everything up, re-assemble, go for a test ride in the snow, and it's still thunking. I get off the bike, rock the crank, and I can produce the same thunking -- but I don't really feel play in the crank, but I figure its moving laterally and needs another shim. Pull the crank again and put in a .5mm shim. Still thunking. Back onto the stand. The bike has a 12mm through axle rear hub (HED), which I had tightened earlier to rule out any issue there, but what I didn't notice is that the hub axle end cap had come loose, which allowed the hub to move laterally. Pull out the cone wrenches, tightened it up and thunking went away. A five minute repair. I don't know how or why the end cap loosened, but I've had the same problem on other wheels with similar thread-on end caps.

-- Jay Beattie.



Yup. It's never where you think it is. I had a bearing-grinding-like
sound in my Domane a few years back. Well, that's what I thought of it
as, I hadn't had bearing sound before.

Put it in low gear on a steep climb, get a click or clunk once per rev
of the crank, but only in lower gears. Well, those have more torque.
It got so bad on a 300k brevet I was getting really spooked (climbing
over Cape Lookout on the Oregon coast).

Replaced BB bearings, greased up the interface well (BB90 bearing
cartridges press directly into the carbon). No joy.

Finally found out it was the "Isospeed" bearing, peculiar to Domanes, at
the joint between seat tube and toptube-seatstay "module". (See any
review of Domane "Isospeed" to see what's going on; this is unique to
certain Trek models; it really does work.) With a low gear, I was
"bouncing" just a bit, actuating the bearing, and carbon is really good
at conducting sound.

All those brevets in the rain had rusted the bearing cartridge horribly.
Replaced them (cheap at the bearing store) and the problem is gone.

Mark J.

PS - I had already tightened the rear QR, having heard about /that/
problem on this NG.