Hello,

Today something really strange happened to me. I've been riding a Btwin Ultra 520 AF GF with a Rival HRD groupset, which uses a yaw front derailleur, for 3000km without issues. Today I was commuting to work in the big ring when, suddenly when I started to sprint exiting a roundabout, I felt like the cranks got stuck. I stopped pedalling and turned the cranks backwards thinking it was chainsuck, but as soon as I resumed pedalling forwards, I noticed a rythmic rub.

After stopping to examine what was happening, I noticed the FD was rubbing the crank and it had left a small dent on the crank paint where it hit. I had adjusted it myself when I bought the bike and I'm sure the clearance was more than enough and the limit screws were correctly set (I check it regularly). After carefully looking at it, it seemed that when the crank struck the FD, it forced it to rotate around the frame tube leaving it in a position that caused interference on every crank rotation. So I untigthened the clamp bolt (which wasn't loose, so it couldn't have moved by itself), aligned it correctly, adjusted the derailleur, checked that there was plenty of clearance with the crank, and continued riding to work without issues.

After thinking about it, the only thing that occurs to me that could have happened is that the yaw mechanism that this FD uses somehow got stuck in the small chainring yaw position, reducing clearance with the crank, and as soon as I started to pedal hard, the frame flexed enough to allow the crank to catch it.

Has someone had a similar experience? I've been riding and doing my own wrenching for ages, including thinks a lot more complicated than adjusting derailleurs, and never had something similar happen. Is this common with SRAM yaw FD?

Thanks

It is possible that the derailleur got hit or kicked while the bike was parked or while being transported.

I have not transported the bike. I guess it's possible that it got hit while parking it in the vertical bike rack I have at home, but I had been riding it for 25km without any stop before this suddenly happened.

I have to ride back home for 50km in an hour... I'll keep an eye on it, as I think it's a miracle it didn't break on impact with the crank.