Rear Derailleur wrapped around cassette
jsnfng
Posts: 4
Hi all,
At the start of the season I purchased a new Trek/GF Cobia hard tail 29er and soon after caught a muddy stick that pulled the rear derailleur off the hanger and mangled it pretty badly.
Shortly after, I picked up the 10-spd SRAM X9 and things seemed to be okay. A handful of rides after having it installed, I took a shallow hop over a VERY shallow rut, my back wheel barely touched the back lip, and immediately my rear wheel locked. I got off to find the X9 pulled back and up, and wrapped around the cassette. Obviously I had to replace the hanger, but the derailleur was fine, and the arm still straight. Note that I was mid cassette in the back, middle ring in front. There was some spoke damage, so I carried the bike back, had some rather extensive wheel work done, and threw a new hanger on there, and it was purring again.
I had been riding consistently for a month (including a bike trip around North Carolina). Then yesterday, a simple bunny hop over a little log, and I ever-so-slightly caught my rear wheel again on the back side of the log. Once again, immediately upon landing my rear wheel was locked, and again the derailleur was wrapped up and over the rear cassette.
Before the second incident, I rode with one of my mechanics (who has been racing MTB for many years) and he noticed nothing about my riding style that seemed abnormal.
I would love if anyone has seen anything like this before. My LBS is baffled, and I would really like to figure out what I may be doing wrong (if anything), or if there is some culprit. My wallet is having a hard time supporting my new bike-part habit...
Thanks
At the start of the season I purchased a new Trek/GF Cobia hard tail 29er and soon after caught a muddy stick that pulled the rear derailleur off the hanger and mangled it pretty badly.
Shortly after, I picked up the 10-spd SRAM X9 and things seemed to be okay. A handful of rides after having it installed, I took a shallow hop over a VERY shallow rut, my back wheel barely touched the back lip, and immediately my rear wheel locked. I got off to find the X9 pulled back and up, and wrapped around the cassette. Obviously I had to replace the hanger, but the derailleur was fine, and the arm still straight. Note that I was mid cassette in the back, middle ring in front. There was some spoke damage, so I carried the bike back, had some rather extensive wheel work done, and threw a new hanger on there, and it was purring again.
I had been riding consistently for a month (including a bike trip around North Carolina). Then yesterday, a simple bunny hop over a little log, and I ever-so-slightly caught my rear wheel again on the back side of the log. Once again, immediately upon landing my rear wheel was locked, and again the derailleur was wrapped up and over the rear cassette.
Before the second incident, I rode with one of my mechanics (who has been racing MTB for many years) and he noticed nothing about my riding style that seemed abnormal.
I would love if anyone has seen anything like this before. My LBS is baffled, and I would really like to figure out what I may be doing wrong (if anything), or if there is some culprit. My wallet is having a hard time supporting my new bike-part habit...
Thanks
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Comments
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With the chain off there is nothing to stop the mech winding back and up and over the cassette, also I guess the chain can pull the mech in, so this sounds to me more like a chain issue than a mech issue.
Is the chain coming off in one piece when this happens or broken? I can't see how, with the chain intact, the mech can do as you describe.Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.0 -
Weirdly the chain does not break. In order to do anything I have to release all the cable tension and get the wheel out because the chain gets too taught to move anything.0
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Very odd. I have a feeling the mech is more twisted than you though, and under heavy impacts to the rear it is bouncing and catching the spokes, and being pulled up by them into the cassette and jamming between the two, locking the wheel.
Can't think what else it could be. Unless it jams in the actual spokes of the wheel, the wheel should just freewheel regardless of what gets caught in the drivetrain?0 -
Huh - that is a good point. In retrospect I cannot remember whether I had to brake or if the wheel locked up. In my head I remember the lock-up, but then the wheel was free when I was working on it...
I have considered the twisted arm as well, but I keep coming back to the fact that it first happened when the whole derailleur was out-of-the-box new.
I am intrigued by the thought of the chain grabbing something and pulling the whole lot over, as the arm itself has been pulled across the middle of the cassette (rather than up by the spokes).0
