help with gears!

[stew-b]

ok before i start i need to say i was a cycle mechanic for 11 years so have a fair idea what im doing lol BUT this one just doesnt want to play!!
i have a 7 speed shimano cassette,age unknown,a brand new 7/8 speed chain and an aging xt rear mech.
problem is the second smallest sprocket on the rear makes something jump like crazy,i have changed the chainset as i suspected worn rings,no joy,brand new chain,no joy,stripped and cleaned cassette,same,cables etc are new and indexing correctly,its jumping forwards not sideways...
i cant work out if its a worn cassette thats doing it though it looks fine or a worn rear mech??
i tried a 9 speed cassette and it appeared to jump just the same but thats with a 7/8 speed chain so not sure what that proves.
its imposible to replicate the fault when not riding it no matter how much pressure i apply.
what i cant understand is why its so much worse on the 6th sprocket,the 7th does it a little and the 5th under a lot of pressure,rest are fine and doesnt matter which chainring i use..
B tension has been tried full in and full out.
any ideas?!?!?!? :? :? :?

http://s28.photobucket.com/albums/c202/ ... f78254.flv

 

[xerxes]

Sounds like the only thing you haven't swapped out is the rear derailleur. What is the chain line like? I'm not sure of the terminology here, but is the rear derailleur jockey wheel cage near verticle when viewed from the rear of the bicycle, or is it hanging at an angle? If the jockey wheel cage is angled too much the chain has to curve to get onto the cassette sprocket.

I hope that makes sense. :?[/url]

 

[stew-b]

mech and frame is straight....

 

[terryhfs]

b-tension? Top jockey hitting the sprocket?

 

[stew-b]

nope

 

[legrandefromage]

mud in the cassette? Something stuck in there causing the chain to catch.

Check the chain for bends

and


the killer for me was the the link use to join the chain together - this fouled on some of the cassette sprockets as on pin was too wide...

 

[stew-b]

i stripped and cleaned the cassette and have tried 2 new chains,with and without posh connectrs.

 

[bojangle]

Stiff link on chain?

Bent frame hanger? (would need correct tool to measure, not possible to detect with eye, trust me!)

worn cassette? (the chain and cassette should mate over time so if you put a new chain on a very worn cassette it WILL skip, i've had it many a time with old and new stuff 7 to 9 speed! The shape of the casette 'teeth' should match the shape of the rollers on the chain)

Chainset and cassette alignment?

 

[stew-b]

2 brand new chains,no stiff links..
i just tried my wifes xtr rear mech on it,still the same.
noticed the last gear outer cable was split so replaced that,still the same....
the only thing i havent tried is a brand new 7 speed cassette cause i dont have one but it looks fine and its only 1 sprocket that has the problem!!!

 

[marc two tone]

gear prob

lets see your shifters mate. is there a chance that the internal ratchety bits are somehow out of true? i.e that particular gear not retracting or releasing the right amount of cable?!
just a suggestion for now.