Derailer problem - any ideas whats causing this

I_M_Weasel

I_M_Weasel

I_M_Weasel

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Joined
10 Sep 2008
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1,646
My bike has developed an issue with the rear mech and jockey wheel cage.

Bike is fine under power, nothing unusual but when I stop peddling the derailer cage violently smashes backwords and forwards and the top of the chain slackens and tightens to match the movements of the cage - typically it pulls the chain off in a few seconds.

I can seehas I'm riding, the cassette is trying to rotate forwards with the wheel this slackens the chain at the top and then the freehub seems to suddenly let go and this takes tension off the cage so it flys forward before the cycle repeats.

I've taken the wheel and cassette off - all seems fine pawls are moving freely in the free hub.

Any ideas on what is causing this?
 
My guess is the free hub.

Get the bike on a work stand or get someone to hold the bike so the rear wheel is off the floor and peddle in a big gear, then stop. My guess is that the free hub won't release and you'll see the problem.

If it is the free hub, have a go at totally cleaning it with degreaser, then use a super non sticky lubricant on reassembly.

I'm totally not a bike mechanic, bit it's where I'd start looking.....

Good luck!
 
It was my first thought too - I was suprised by how freely everything was moving in the freehub - I was expecting (hoping for) a gummed up pawl. Never the less I degreased it, cleaned it, re lubed and refitted - all seems fine at home I cant replicate the issue at home.

I take it out for a test ride and it is immediatly there - I've tried with more lube, less lube, grease, no grease - nothing makes a difference.

I think I may have found the issue though and an explanation as why it is only manifesting when ridden. There is a lot of play in the pack wheel, so much that when weight is on the bike the wheel leans over against the cassette and freehub - jamming the two together and creating a large amount of friction - back at home without the weight of a rider the two parts aren't being pushed together so I haven't been seeing the cause.

I think I need to replace the wheel - its an older bike though and I'm relly struggling to find one.

Thanks for your thoughts.
 
I think my new bike does this a bit, had just thought it was a symptom of a clutch mech but I guess not.

I had better get on to Wiggle in the AM I guess and ask what they suggest!
 
I did source a new back wheel and it has solved the issue - also has stopped a creak that I was getting that I was certain was coming from the BB - evidently ot was the rear wheel hub.
 
Glad it's sorted. What hub was on the old wheel? If it was a cone/ball type affair was it simply a case of tightening the cones?

If it had sealed cartridge bearings, can they be replaced?
 
Cartridge bearings - I can't see how I would get them out and probably not worth it -I've pulled the rim tape off the wheel and there is a crack running for about 10cm on the inner surface of the wheel. I can't complain it's done years and 1000's of miles of off road riding - I've had my money's worth.
 
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