[Sam Mashford]

Hi All.

I have a bike, custom, steel frame, ultegra di2.
Had it since July 22.
Now I have a mind boggling issue.
Periodically, particularly since April last year, when I use a certain gear combination (I think 50t front and then the 10/11spd of the cassette) something snags – feels like chain suck, catches the front derailleur and results ultimately in a twisted derailleur boss. One time a cracked one.
It’s had cassettes, it’s had chains, it’s been checked for alignment it’s had a new boss and partial respray and last time a new front derailleur.
It’s still an issue any ideas? Any experience of something similar

Topic

[Sam Mashford]

Apologies, didn’t see this and only found it when I came back to say no..
So rear hub got a good lube and service.
All seemed fine, not done a lot this year at all, dropped into 10/11 on the cassette, big ring up front, soft pedalling and clink clank clunk.
Managed to not bend the brake on this time and got derailleur in to the right position, went out the other day 45 miles didn’t use 10/11 deliberately, everything ran like a dream…

[ErnieC]

Sam Mashford wrote:

Sam Mashford wrote:

Ooh now that’s an interesting thought! I’ve got Chris king hubs, I’ll have a look at that

Have you manged to resolve this yet?

[Sam Mashford]

Ooh now that’s an interesting
Ooh now that’s an interesting thought!
I’ve got Chris king hubs, I’ll have a look at that

[thax1]

Sticky freehub/freewheel?

Sticky freehub/freewheel?

Allowing the ‘top half’ of the chain (above the chain stay) to go slack or kink when you soft pedal /stop pedalling? Then the kinked chain is catching on the FD when you start to pedal again?

I had a freehub that was a bit lazy to disengage, especially when you were on and off the power to close a gap on a fast descent. Used to give a load of chain slap, and a clunk feeling as the RD arm spring got the chain tension back under control.

[David9694]

You are Nessa from Gavin &

You are Nessa from Gavin & Stacy and ICMFP.

[Sam Mashford]

I don’t think it’s
I don’t think it’s restricting position but obviously there’s no flexibility with it, so I have considered going down that route but that would be a case of treating a symptom rather than the cause I think?

[Pub bike]

Sorry if I’m stating the

Sorry if I’m stating the obvious here…if the boss is restricting positioning and/or you don’t want to have yet another respray you could remove it altogether and use a clamp e.g. one of these.

[Sam Mashford]

Not going to lie, it did take
Not going to lie, it did take until last time it went to check that, which was probably the 5th time🤦, but yes it’s straight. But I am also on that train of thought that it’s not the FD, but all frame alignment is ok, RD hanger fine, FD mount is ok (again). Was hoping Shimano would have a known issue and just say it’s this…

[Rendel Harris]

Have you checked the rear

Have you checked the rear derailleur hanger isn’t bent? The fact that it’s only catching in what presumably is your highest gear suggests it may not be an FD problem at all. If the hanger or (hopefully not!) dropout is bent it can affect the chainline so that it catches on the front. It might only do that under a certain load which would explain the intermittent nature of your problem. Worth a look anyway.

[Sam Mashford]

They’ve also been changed,
They’ve also been changed, not that they needed to, I’ll have a look at the B screw, I’d have thought it would cause problems more regularly than it has though?

[Sam Mashford]

I don’t think that’s been
I don’t think that’s been happening and I don’t like the sound of finding out that’s the issue!

[Sam Mashford]

Yeah it’s been checked and
Yeah it’s been checked and set up by 3 different people, new bolts, washers, new derailleur all sorts to make sure it’s in the right place and can’t move

[ktache]

How are the jockeys looking.

How are the jockeys looking.

And might this involve “b” screw adjustment?

[mark1a]

Have you checked the height

Have you checked the height of the front derailleur and distance between it and the big ring? Should be 3mm IIRC. If it’s too close or too far, it can jam when changing at the front. Easiest way to check is by using the flat sides of a 3mm hex key.

I had a similar issue a few years ago on Ultegra R8000 Di2 front derailleur. Fine-tuning the height as above sorted it. 

[David9694]

A while back with Ultegra

A while back with Ultegra 6800 I had a similar issue where on a FD gear change the RD would just lock up and you had a split second to realise that the derailleur body is moving towards oblivion not the chain and stop pedaling. Never got to the bottom of it still live slightly in fear of it happening again. 

[Author]

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