Poor shifting - replace rear derailleur?

[blimpnoddle]

Shifting is poor and when in any gear it isn't smooth. I've tried to adjust tension etc but it makes little difference. There is some play where the mec attaches to the hanger but tightening the relevant bolt makes no difference. Does anyone know why this is the case? I have fallen on that side a few times but the hanger doesn't seem to be bent.

So do you think the mec needs to be replaced? It's a 2300 on a 6 year old Triban 3. If so, would a Sora work with the 8 speed cassette, and does it need to be long cage like the existing 2300 because I can only find medium or short cage?

 

[Yellow Saddle]

No.
Check the cables (have someone competent check them or just replace them outright.
Straighten the derailer hanger.
Drink a beer.

 

[sleuthey]

Have you tried replacing the cable? If you cut the outer a couple of inches too long at the shifter end then if it does not work you can replace the mech and use the same cable by trimming it.

 

[fossyant]

How old are the cables ? That's usually the main cause of poor shifts, and bent hangers

 

[Pale Rider]

The hanger only needs to be bent a tiny amount to cause clonky shifts.

Straightening such a small deflection may not be easy without the specialist tool for the job.

Replacing the hanger is a more likely cure than replacing the mech.

Hangers can be bought 'by shape' online.

https://derailleurhangerstore.co.uk/

 

[roadrash]

while your at it check the cable guide under the bottom bracket, its a prime place for getting full of shyte

 

[Racing roadkill]

Try straightening the hanger, and putting some new cable in first ( inner and outer ). I had an issue with the mech you have there, which was basically where someone crashed into the back of me, on a ride, and their brake disc fitted perfectly between the plates of the cage, and buckled it, that was game over for that mech, but usually a hanger straighten and re cable does wonders.

 

[Racing roadkill]

while your at it check the cable guide under the bottom bracket, its a prime place for getting full of shyte

Indeed it is, on that particular bike, the cable guide that was supplied is a bit shyte, and prone to splitting at the divider, it’s worth checking.

 

[Ajax Bay]

Shifting is poor and when in any gear it isn't smooth. I've tried to adjust tension etc but it makes little difference. There is some play where the mec attaches to the hanger but tightening the relevant bolt makes no difference. I have fallen on that side a few times but the hanger doesn't seem to be bent.

These symptoms fit a diagnosis of hanger/rear mech (mis)alignment (as others have already said, hail @screenman) and quite likely the falls on it have bent the hanger.
The hanger attached to the frame needs to be exactly vertical. Check the little screw(s) attaching the hanger to the frame are secure/tight. I would se threadlock on them.
It's not easy to ascertain the hanger is vertical just by looking. The threaded hole in the hanger is generally the same calibre and thread pitch as the rear axle. I use half a (broken) axle - unscrew the RD (rear mech) and screw in the axle. With the frame vertical, the axle screwed into the hanger should be horizontal. This is easier to see (because even half an axle is much longer than the hanger).
If not vertical, you can bend it back - but do this is in one go as every 'bend' weakens it. If/when this allows your shifting to be much better, enjoy it and ride. And procure a replacement hanger for fitting when received.
If the RD cannot be secured (screwed) to the hanger without play, you need a new hanger.

 

[cyberknight]

before you go fown the hanger route check your cables , especially the outer that curves arund to go into the derailleur , thats prone to gunking up and causes the issues you have,