For the second time in as many years, I have had a very odd bike malfunction. This occurred on two separate bikes, different brands.
While riding a mountain bike, slowly and during gear changes, I have had the chain and rear derailleur get jammed up somehow and before I became aware of it, the chain (I assume) pulled the derailleur out to the side drastically. The rear derailleur was either bent beyond repair or completely snapped off. The chain was damaged by twisting in both cases. This malfunction naturally rendered the bike unusable until repaired.
The commonalities, coincidental or meaningful, between these two cases are these: 1) mountain bikes, 2) slow speed travel, 3) gear changing or soon after, 4) derailleurs slightly out of adjustment (prior to tuneup), and 5) derailleurs were Shimano.
There is one mystery here, but a couple of questions that are closely connected.
The Mystery: I rode and worked on bikes a lot many years ago (most of the shift bikes were Schwinn). After years off, I started riding again about 3 years ago on mountain bikes. I have never had this derailleur problem prior to my recent riding. Then, after taking up riding again, on two separate bikes, this malfuction occurs.
Is it possible that some design change in rear derailleurs over the last 10 years or so might be contributing to this problem by making the derailleurs more fragile or more prone to lose calibration?
What could I be doing to contribute to this problem?
Thanks for any light you can shed.