On my Canyon Ultimate with Ultegra Di2 11 speed drivetrain I just replaced the chainrings and when I put everything back together the chain is super slack when I shift into the small ring. Any ideas on why the slack chain would pop up?
I’m wondering about the bottom bracket being freshly cleaned and lubed, versus the freehub and/or derailleur being “gunked up” for lack of a better descriptor
And any guidance on cleaning/lubing the rear derailleur if that’s what it is? Thanks.
First check would be check new chain rings are same size as old chainrings - ie did you accidentally buy smaller rings. Also, did you replace chain? And if yes, did you cut chain to same length as previous chain?
Same chain. Same inner chainring. I did swap the outer chainring from a 52 to a 53 and realign the front derailer.
Did you take the rear deraileur off in the process? Might not be installed correctly.
did not remove rear derailleur.
k - so how “slack” is it - ie where is mech pulleys in largest cog when in small chain ring (normally they would be in close to straight line in the 6 o’clock position to the axle - if they are in say the 7 o’clock postion or even 6:30, then yes chain will become too slack in smallest cogs).
and then yes if its back from 6’oclock and so really slack in smaller cogs - if the chain ring size is same, and the chain is the same length - honestly it would be SUPER odd for that not to have been exactly the same situation before - but maybe you didnt notice it?
If freehub is “gunked up” - which is uncommon, more common is lubricant starts to run out which could cause poor performance with ratchet engagement / disengagement, that presents with other problems (if it does’nt engage you will sure know about it, if it doesn’t disengage the cassette will keep turning when you stop pedalling and drive the chain off the chain ring).
A rear mech “gunking up” to cause this would also be exceptionally unlikely. The pivots which are exposed and in theory maybe one day need cleaning and lubricating (i have never done this with a mech ever, and all mine run like the day i bought them - over 60k km later on oldest road bike, and over 10k km on oldest mtb mech that sees a lot of bad conditions riding) - but if they start acting up - that will affect shifting.
To affect chain tension - that would come from main body spring (what is adjusted with B-Tension), and this is sealed, and they typically never need lubrication. A slack chain from this part of mech can happen - if spring breaks, or is somehow become very weak over time (takes a long time).
Basically if you push rear mech towards chain ring as if you wanted to get bottom span slack to remove master link etc, if it doesn’t come back with nice spring tension to hold chain firm - then you may have a spring issue - but again whilst this happens, its RARE. And that it happened exactly when you changed chain rings and chain……… we have some long odds.
If it isn’t main body spring and that is pulling back with normal tension - honestly it really only leaves chain length and chain ring size (also - unless someone messed with b-tension setting and set that way wrong which could have chain very slack).