The chain of my bicycle slipped of the top sprocket and cause the derailluer case and hanger to bend. Anyone experienced this?

Edit - More Info:

I crashed a couple days ago before the derailleur got bent and after the crash, I realized that when I try to shift to the big sprocket stationary ,it sometimes will slip off and goes to the back of the cassette. I thought it won't be much of a problem and told myself just to not try and shift to the largest sprocket. But during that time when I was cycling, I tried to shift to the second largest sprocket but accidentally shifted too much and I think that caused the chain to slip to the back of the cassette.I was pedaling really hard at that time and I think that bent the derailleur.

The derailleur was really badly bent since it was facing up, I had to push it back to its original place as the bike would not move. After I did that, I saw that the cage plate (if I'm not wrong) was bent towards the spokes, applying pressure on to them, and making that ting ting sound. So I used some force to try and bend it back so I could go home. Now that I'm looking at it, I saw that the cage plate was both twisted and bent and the rollers are not aligned. The chain is also not on the top roller and is laying on the the cage plate.

Edit:Changed the rear ,working fine now. Thanks for all the help!

  • Probably the chain and rear cluster were worn out (and then some). – Daniel R Hicks Jul 4 '16 at 11:04
  • Your bike is probably a "bicycle-shaped object", so $20 will not only replace the derailleur but represent an upgrade. – Kaz Jul 4 '16 at 14:28
  • Yeah thinking of replacing one – Banana Cyclist Jul 4 '16 at 14:30
  • I'll note that any time the chain jams it's possible to do significant damage by forcing the crank. I suspect that if you had stopped pedaling as soon as you sensed the hangup then there would be minimal damage. But likely shifting was flaky to begin with (due to misalignment and/or excessive wear) and you were used to forcing through brief "hiccups". It's just that you finally ran out of luck. Of course, when you throw the chain into the spokes it's often not possible to stop before things go from bad to worse. (Those "sissy" spoke protectors have a purpose.) – Daniel R Hicks Jul 4 '16 at 20:46
  • I thought it would help in preventing the chain from going behind the cassette too, but it doesn't help much. – Banana Cyclist Jul 4 '16 at 22:23

I crashed a couple days ago before the derailleur got bent and after the crash, I realized that when I try to shift to the big sprocket stationary, it sometimes will slip off and goes to the back of the cassette:

It sounds like the derailleur was already damaged in this crash, causing the shifting to be off. Perhaps the hanger got bent, causing the cage to point inward, throwing the entire shifting alignment in the direction of the wheel hub, thereby allowing the chain to derail from the largest cog. This is a bad situation if, additionally, the derailleur makes contact with the spokes.

In this situation, the lower limit trim screw won't help, because its action plays out in the pivot mechanism above the cage.

If you're prone to damaging your derailleur, consider installing a derailleur guard.


Of course most everybody has fallen on their derailleur from time to time.
* A derailleur has worn out when the play in the derailleur exceeds a certain amount. Falling on it exacerbates that wear. * Sometimes, the derailleur hanger bolts loosen over time, more so when you fall on the derailleur. Check these bolts are tight.
* The derailleur hanger (you called it a plate) does get bent. To bend it back, you should first take off the derailleur, make sure the derailleur hanger bolts are tight, and stick a metal rod in to bend it back. Only advisable for minor bend. If you bend it by grabbing the derailleur, you will introduce more wear into the derailleur.
* For a more professional job: Some bicycle shops have tools to check the hanger is aligned, and may be able to take it off the bike to align it in a press, although I suspect most would just leave it on the bike and bend it with a rod, as above.

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