Derailleur problem

Donski
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Joined: Sun Nov 05, 2017 7:31 pm

Derailleur problem

Postby Donski » Tue Nov 28, 2017 3:28 pm

Riding home from work and my rear derailleur jammed on me. Seems like the chain is slipping off the lower jockey wheel and the whole thing has come completely out of alignment. Do I need a new derailleur or could it be fixed

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trailgumby
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Location: Northern Beaches, Sydney
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Re: Derailleur problem

Postby trailgumby » Tue Nov 28, 2017 3:39 pm

If you have some photos or a quick youtube vid it would be helpful.

Derailleurs are pretty hard to kill, although I've almost managed it with a stick getting caught up in the chain and back wheel on a mountain bike trail, and I was a bit slow getting off the loud pedal. A bench vise and a rubber mallet straightened and resurrected it, and it lasted the life of my ownership of the bike.

That said, if it's jammed and you didn't stop pedalling fast enough it could be bent. You should look at the derailleur hanger alignment as well. If you are handy it could probably be fixed. If that sounds a bit daunting or you're not sure what to do, buying a replacement RD won't be that expensive.

Might it just be your jockey wheels are stuffed? You could consider getting some BBB Rollerboys - replacement jockey wheels. They are very hardy and long-lasting, and it doesn't hurt they spin on ball races - easier to pedal.

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open roader
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Re: Derailleur problem

Postby open roader » Tue Nov 28, 2017 3:43 pm

Answer is ..............it depends...........

If the chain is actually falling off the lower jockey wheel the cage must be split enough for it to pass the lower jockey wheel's axle or else the chain is not running over the jockey wheels in the correct way. If the chain is simply droping off the bottom of the jockey wheels then it's possible you have stuffed the bearing in the jockey wheel/s - this aspect of your post I find perplexing - the actual dropping off the jockey wheel part (yes pics might help but I see you are at only 5 posts)

If the cage is badly bent I'd say replace as I've never had any luck trying to re-align bent cages without some sort of noise or shifting issue.

If the cage is still aligned and the derailleur hanger is bent then it's simply a matter of re-aligning the derailleur hanger - something I've had plenty of success with.
3rd class cycling is always better than 1st class walking

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trailgumby
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Re: Derailleur problem

Postby trailgumby » Tue Nov 28, 2017 3:55 pm

open roader wrote:If the cage is badly bent I'd say replace as I've never had any luck trying to re-align bent cages without some sort of noise or shifting issue.

Requires partial disassembly - at least removal of one side of the cage and straightening each independently. In my case the knuckle was also bent... rubber mallets rock. Most would have discarded at that point but I decided to have a go and see what happened. I ended up lucking out. That decision was in part driven by it being a low normal RD - not exactly common.

But yes, if it has obvious stress marks when you straighten it, replace.

Donski
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Joined: Sun Nov 05, 2017 7:31 pm

Re: Derailleur problem

Postby Donski » Tue Nov 28, 2017 4:03 pm

Yeah just tried changing the jockey wheel, works a little better in the lower gears but still slips off the wheel in the high gears. Also noticed the bolt holding the hanger to the bike was loose which might be why it slipped and jammed. Think something got bent when it jammed.

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