Di2 Rear Mech Creaking/Grinding

superkenners

I've had a grinding sound on the back of the bike (most audible when putting some torque through the pedals when accelerating, most noisy in the top half of the cassette (18-28 i suppose) but there most of the time when accelerating on both big and smaller front rings.

Have had bike down to the bike shop, everything stripped down the problem seems to be the Ultegra 6870 Di2 rear mech. Mech looks fine (not been crashed) and works fine for all intents and purposes. Shifting is smooth, everything straight on bike (had new hanger). Jockey wheels look good. It just makes a really loud creaking sound, as if something is bent or bending when power goes through. Once up to speed runs fine, sound not noticeable. Switched out for Dura Ace mech and sound gone. So mech seems to be the fault. Seems to be some flex when under a bit of power. Only done 1600 miles on this and been like this for last couple of hundred. Gets no worse, but a bit disconcerting. Wouldn't like it to fail going 40mph downhill.

So two questions, has anyone else had a creaky/grindy rear Di2 mech that seems to be perfect when examined??

And would you replace like for like (another 6870 mech or go for the 8050 which seems to have improved design (cost on Chain reaction not too far apart so that's not an issue)??

Thx

pilot_pete

Presumably it is under warranty, get the bike shop to replace it...

PP

superkenners

Out of warranty unfortunately.

shirley_basso

viewtopic.php?f=40004&t=13085478&start=60

This thread also displays the same issue, albeit from a different groupset.

I assume it's not a chainline issue? Does it occur in the small ring as well?

superkenners

Thanks for link to that thread.

Happens on small ring too. Once up and running its fine and not a shifting problem as switches between the gears is perfect. It just sounds like you're pedaling a diesel.

Annoying thing is it was silent for over a thousand miles before this problem started.

pilot_pete

Superkenners wrote:

Out of warranty unfortunately.

You’ve only done 1600miles in two years? Or was it not new when you bought it?

PP

p.s. Are you sure the cassette carrier hasn’t got a broken/ loose rivet?

pilot_pete

Shirley Basso wrote:

https://www.bikeradar.com/forums/viewtopic.php?f=40004&t=13085478&start=60

This thread also displays the same issue, albeit from a different groupset.

I assume it's not a chainline issue? Does it occur in the small ring as well?

Not really the same issue; that thread is about a noisy group, not one that is making a creaking/ grinding sound.

PP

superkenners

Yes, its the summer bike but haven't had much time from basically the time i got it, hence the low miles. Bit annoying.

Will double check the cassette.