Bike jumping rear gears

[Markymark]

Took my hybrid in for a service at my LBS and they put on a new chain and rear casette. Immeditaely afterwards it started jumpng gears (maybe 3-4 times per 10 mile commute). Mostly seemed to be changing down a gear.

I tried adjusting the deriallers and made it better but still not ok. I took it back to the shop who adjusted it all for me, nows its as bad as it was first time around. Its killing my right knee as it gives way when pulling away from stationery (I'm guessing its becasue I am changing down a gear coming up to the lights ands its not shifting properly).

I'm taking it back to the shop who said they would invesitage furtehr but is this just a case of gettign the adjustments right or could something else be wrong (wrong cassette/chain fitted)?

 

[green1]

could be a bent chain link.

 

[Ian H]

Possibly a tight link. Turn the pedals slowly and watch the chain for any links that don't straighten properly. Loosen by vigorously bending the chain sideways back and forth, or with a chaintool (carefully, especially if it's a 9 speed or more).

 

[Markymark]

Ta, will look at that tonight. I studied the chain going round the cassette for ages so don't think there is, but I wasn't looking for bent link, so possibly!

 

[Ian H]

Actually, reading your first post, I wonder whether you are changing too late and stopping with the chain halfway across two sprockets.

 

[Markymark]

Actually, reading your first post, I wonder whether you are changing too late and stopping with the chain halfway across two sprockets.

I'm certainly no expert cyclist but have ridden c3K miles commuting the last 18 months and have not changed my gear-changing habits so its only the new chain/cassette that has changed.

I am sure what you are sayign is correct and that it is not having time to change, but I never used to have a problem so its definitely not workign as well as it did (should).

 

[Ian H]

Perhaps take it back to your LBS. Tell 'em it only happens under load, so they need to road-test it. I also wonder whether whether the new chain is longer than necessary.

 

[MrJamie]

I got a smiliar thing after replacing chain and cassette. I couldnt find any stiff links on the chain, all moved round fine as far as i could see, but i would still get slips under heavy load out of the saddle, which is never fun when pulling out into traffic. I also thought it might be the chainrings, but they look pretty good and im fairly sure it was slipping at the back not the front. Like you i put it down to a messed up downshift approaching the junction/hill but also combined with significant frame flex when im out of the saddle. Anyway, the indexing got progressively worse until i noticed the end of the outer cable wasnt seated correctly in the rear derailleur so the shifting wasnt precise and the cable was burried in crap under the bottom bracket which can cause "ghost shifts". Probably not much help to you, but might give you some ideas of things to look at.

This was quite relevant to me: http://sheldonbrown.com/autoshift.html

 

[Ian H]

Yup. All relevant.

 

[Markymark]

Thanks all.