kcjc

The discoloration of the material around the failure suggest it's caused by galvanic corrosion possible between the cage and rivet but I don't have the means to verify or want to spend the money for. Just curious if anyone seen something similar. The only thing that I have seen is actual rusting eating through the cage on low end stuff that's many many years old and not cared for. The derailleur was purchased 8/2016 and used exclusively indoors. I average around 100 hours a year indoors mostly sim mode (~2/3 on sim & 1/3 on erg). So basically not that much use. My Dura Ace 7400 from back in 1989 was basically indestructible and I had it until 2014 when I donated the bike. Other dark stuff you are seeing are from the wax chain.







minor rusting at the pins

Crankycrank

Many bikes used for indoor stationary training get corrosion from salty sweat dripping on parts. Give it a wet wash every once in a while or use a towel to cover the bike and catch the sweat. There are also special guards made for this. bike trainer sweat guard for sale | eBay

Andrew R Stewart 

Looks like salty sweat induced corrosion. 100 hours a year on a trainer is not minimal use. Not unlike the many ft ders that are winter toad salt damaged we see every off season. Andy

kcjc

The bike get a wash every month or so and been using the bike bra since day one. SF Bay and central California roads so never seen salt damage. There true rust on the derailleur on the pivot pins and elsewhere on the bike especially the front wheel so the discoloration was weird. Thanks.

Andrew R Stewart 

And yet this corrosion problem still happened. A bra, or the ones I remember back when trainer stands came onto the market, don't do a good job at the seat end as that's where the bra is the narrowest and only covers forward of the post. BTW when was the last time the post was pulled and checked? Andy

kcjc

Around April 2022 but I recently play around with the alignment and it's still moving. I switched out the Ultegra drive train (except the front which is DA) to Sensah Empire Pro around April. I tried to install a chain catcher in December but the combination didn't fit the well, the derailleur kept slipping from the adapter clamp braze on extension and I ended up stripping the nut on the derailleur body. Put the DA derailleur back on temporary until I got replacement parts. I didn't notice anything until I was dropping chains like crazy. It was one of the reason I changed out the group set. The other being the screw to the bottom access panel on the shifters was complete rusted out and I got tired of eating cables. The chain catcher on the Sensah was insurance.