Rear mech hanger chain rub

[tinchy]

Hi all,

So - circa 1 year old 105 rear mech, new chain and cassette recently installed.

When riding in the big ring up front and admittedly, cross chaining, I was getting a reasonable amount of 'chatter' from the rear casette/rear mech area when in the top two (largest) sprockets.

Upon closer inspection, I can see that the chain is gently rubbing the rear mech hanger cage in these two top gears.

My instant thought was a bent mech hanger, but the shifting is spot on so I ruled this out. My only other thought is the bearings in the pulleys are shot/theres too much play in the lower pulley that it cant hold its own and help keep the chainline straight?


Is this normal, a result of cross chaining, or should I just stop being stingy and splash out on a new rear mech?


Keen to hear your thoughts!

[Rick]

I think shifting can be "spot on" even with a misaligned hanger, and the symptoms would be similar to what you describe.
So I would start with a hanger alignment anyway.

[mattr]

Yeah, you can get a combination of twist and bend that means the shifting is still ok, i had it on my MTB, gears ran perfectly for a couple of years after a "field fix".

Put an alignment gauge on it and it was WAAAAAAAAAAY out.
Seen it in a couple of other bikes.
Probably worth a look.

(I've got a 2 year old 105 mech which i abuse endlessly, high load shifts, cross chaining and so on. No chatter on that.)

[tinchy]

Yeah I agree, perhaps the cage has somehow twisted slightly in a way that still permits shifting.

At the end of the say, I understand how cross chaining places extra stress/wear on the drivetrain and should be avoided, BUT, it should still be mechanically possible if the drivetrain is set up correctly. Clearly it isn't in my case, so off I will trot to buy a new rear mech.

Thanks both for the help.

[mattr]

Hanger first. THEN rear mech.

[tinchy]

Indeed