Crankycrank

I gotta ask. When you put the bike in the car do you take care to not bump or set it on the derailleur getting it in and out?

Pavol Stromcek

Obviously, I'm super careful about that.

juls

Is not small small combo, cross chaining? I realize that would not cause the kind of damage depicted/but would twist the chain causing more unneccesary wear to gear teeth. Especially uphill with load to the trane. Interesting post.

Johno59

I have seen this exact same carnage. The power needed to cause such distortion suggests your new chain was too short. A friend of mine had his titanium super record rear mech destroyed this way. He had a new chain fitted coz he was going to a very hilly area and decided to get a fresh chain and a new lower geared block at the rear. Everything fine, got to a monster ascent, selected the lowest rear gear (biggest one at the rear) and bang. Basically the too-short chain drew the jockey wheels and cage forward until it was virtually level/ horizontal with the chain line and as such it was understandably destroyed. Because he was giving full power for the steep climb the forces carrying the broken tensioner assembly were immensely damaging as they were pulled up and over the rear block

Check the chain length on the lowest gear back (biggest rear cog) and biggest chain-ring at the crank. Take note whether your tensioner assembly is being drawn forward beyond the 90 degrees and how far upwards into a horizontal (fatal) configuration.

Pavol Stromcek

Well, this story may have a happy ending. I took the bike back yet again (for the third time since the incident, if anyone's counting), and I lucked out by getting one of this shop's best mechanics - a super knowledgable, friendly, and informative guy who was already familiar with the backstory of my bike. He did a full adjustment of the new rear derailleur and even replaced the shifter cable, all free of charge. He did all the work right then and there, in front of me, and had me take the bike on a couple of test rides until everything felt perfect. Even though this guy had by far the easiest of all the repairs done to this bike as a result of the incident, his attention to detail was reassuring. (As it turns out, I'd actually met this guy years ago, through a friend of a friend of a friend, and that may have helped.) I still don't think I will return to this shop in the future, but I might consider it if I'm able to get this one guy to work on the bike.

LKA 

That is the gnarliest damage I've ever seen, outside of crashes. To the OP, you are to be commended for not going full-aggro on the LBS. It's not even my bike, & I'm pissed off for you.

My own goodbye to LBS story: A crash back in 1990 took out the fork & front wheel of my Miyata. So I took the frame & new uncut fork to the LBS to get new headset cups installed along with the steerer tube cut. As it turned out, the steer tube was cut too short & the locknut only engaged 3-4 threads. A constantly loose headset was my reward. The LBS told me to buzz off. In a way I'm grateful...due to that mistake I learned how to do everything that came along myself, and have never gone back to an LBS since, except to buy things.

Question everything, trust no one.

Epilogue: That LBS went out of business long ago. And I re-used the 1st gen 105 front hub from the wrecked wheel to build my very 1st wheel. Sometimes one's own confidence is built upon the failure of others.