Rear derailleur Problems
 

Hi there, I'm running Shimano 105 10 speed with a triple chain ring on the front and have been having some wee issues... I bought a new gear cable for the front derailleur and needed to tighten it, but after doing so (and I don't know if the two events are related, this is just when I noticed the problem) the chain seems to be slipping on the rear cassette, or changing gears spontaneously (I'm not sure which I haven't actually watched whats happening). Basically, while pedaling the gear seems to change and the chain seems to move (I am guessing the gear is changing spontaneously) Does anyone have any idea what could be causing this, or have had any similar problems and could provide guidance? Cheers.

1. Could be caused by excessive chain wear...how old is the chain?
2. Could be caused by excessive cassette wear...how old is the cassette?
3. Could be caused by improper adjustment of the rear derailleur, not being centered on the specific gear.

SHIMANO TECHNICAL DOCUMENTS

Google is your friend.

Check the mechanics forum. You're probably not going to get any advice in this forum that will be useful. Funny perhaps, but not useful.

first just get it on a stand, or hang it by the saddle, and turn the cranks. if it's skipping up or down without any shifting, turn the barrel adjuster on the rear dr the opposite direction to which the chain is skipping until it stops. continue turning the cranks and twisting the adjuster until noise increases, then back off a little till you find the quietest sweet spot.
if that doesn't work, it may be time for a new chain (it probably is anyway, i'm just guessing) but often if the skipping can't be corrected by proper rear derailleur adjustment it's time for new chain/cassette combo.

Try changing to a different saddle, perhaps one with a cut-out. Wee issues are unlikely to be related to your drivetrain...

Hahaha... I think you might be right about that.