Can a cable stretch this fast?

[lulubel]

Sorry to be a pain with more gear questions.

Having sorted the indexing on my chainrings, I now think I may have a problem with the cassette.

When I picked my bike up from the LBS, the cassette was beautifully silent when the cranks were turning, with none of the horrible rattling I had been getting. On today's ride (I've now covered about 70 miles with the new chain and cassette), I started to get a buzzing noise in sprockets 2/3/4 (counted from large to small) while using the middle chainring. This is similar to the buzzing that preceded the rattling that led to my bike's long stay at the LBS.

Is this an indexing issue? Can the cable have stretched already? (It is a new cable, and I know new cables stretch). Which way do I need to turn the barrel adjuster to increase tension if this is the case?

Or is it simply due to my lovely new cassette picking up dirt that the chain has carried over from the chainrings?

 

[Sittingduck]

Is this an indexing issue? Can the cable have stretched already? (It is a new cable, and I know new cables stretch). Which way do I need to turn the barrel adjuster to increase tension if this is the case?

I doubt it's cable stretch. In any case, you need to turn the barrel anti-clockwise to increase tension. Might be worth checking the lockring hasn't come loose, if a new cassette has just been fitted?

 

[RecordAceFromNew]

Often the so called cable "stretch" phenomenon is due to the cable outer not seated completely in the ferrules when installed (e.g. if a ferrule is a tiny bit too small for the outer, or the outer is a bit wonky having had a less than perfect cut). Giving the cable a couple of really good yank when the the bike is in the gear with the highest cable tension before getting the indexing right might help.

 

[actonblue]

One of the causes could be that the mechanic has not seated the outer cable fully in the cable guides on the frame.
If this is not done initially when the outers do eventually bed themselves in this can lead to the poor indexing that you are experiencing.
I would just re-adjust your rear dérailleur using the adjusting barrel. Make sure the cables a are fully seated by giving them a good tug. However do not do this if you have a carbon frame as you could end up pulling off the cable guides.