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?
I assume we are talking lower end der’s here? Personally I have never had a problem with der’s higher than Shimano LX level. However, I have had a world of hurt with ghost shifting and the like.
Until… I recently moved to the wonderful world that is SRAM.
If you are riding a mid end or up mtb bike I cannot recommend the SRAM stuff. X7 or X9.
My new bike is devoid of any Shi(t)mano products and I am loving it.
[quote=“AWOL”]I assume we are talking lower end der’s here? Personally I have never had a problem with der’s higher than Shimano LX level. However, I have had a world of hurt with ghost shifting and the like.
Until… I recently moved to the wonderful world that is SRAM.
If you are riding a mid end or up mtb bike I cannot recommend the SRAM stuff. X7 or X9.
My new bike is devoid of any Shi(t)mano products and I am loving it. [/quote]
I think the derailleurs are lowend, but not certain. I just purchased this Giant Yukon bike and the model of rear der on it is called “Acero”. The front der is “Altus”. So, are those lower in quality than LX?
Don’t want to get this off-topic, because I’m still trying to figure out what is causing the derailleurs to break, but … if not Shimano, what should I replace them with?
[quote=“seeker4”]I think the derailleurs are lowend, but not certain. I just purchased this Giant Yukon bike and the model of rear der on it is called “Acero”. The front der is “Altus”. So, are those lower in quality than LX?
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I checked the Shimano web site and I would wonder about the parts. The Acera is the 6th level down from the top and the Altus is the 7th. I’m sure the parts are functional, but you would have to think that they are a long ways from the Top-of-the-Line XTR components.
you are riding up slow steep hills and changing gears a little late under load…if you are changing several gears at once, trying to get that big gear on the back for the suddenly steep climb, then with a sloppy chain and a low tension rear derailleur not feeding the chain across the cogs to each one for long enough for it to grab and advance the lower end of thechain coming off the idler wheel inwards, the chain will be forced through too large an angle for it to lift off the lower sprocket, where it will grab. this will hold the chain on long enough for it to exert extreme pressure on the derailleur arm, jamming the chain against the inside of the cage and perhaps even bend the arm inwards. your legs are pushing at a large mechanical advantage at these low gears, and the force generated is pretty big.
i know, i’ve done it myself. sloppy gear changes after crashing and damaging the rear (deore gear).
you are riding up slow steep hills and changing gears a little late under load…if you are changing several gears at once, trying to get that big gear on the back for the suddenly steep climb, then with a sloppy chain and a low tension rear derailleur not feeding the chain across the cogs to each one for long enough for it to grab and advance the lower end of thechain coming off the idler wheel inwards, the chain will be forced through too large an angle for it to lift off the lower sprocket, where it will grab. this will hold the chain on long enough for it to exert extreme pressure on the derailleur arm, jamming the chain against the inside of the cage and perhaps even bend the arm inwards. your legs are pushing at a large mechanical advantage at these low gears, and the force generated is pretty big.
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Sounds plausable. I’ve gotten more help on some bike-oriented forums. The answer that sounds best so far is improper shifting leading to chain damage leading to derailleur damage. The remaining mystery is that, while all similar explanations (like yours above) mention the derailleur being pushed inward, my derailleur bent outward.
In any case, a new derailleur and chain later, I’m back in business and shifting a lot more gingerly.
