Weird Behaviour Campagnolo Potenza

[Sillyoldman]

I have 1600 miles on my Potenza 11 speed group set. 11-32 cassette with medium cage rear derailleur on a Mavic Kysrium Pro SL wheel. Both front and rear shifting is and has been wonderful except....
Recently I have experienced the cassette feeling to have locked up. It has only happened 3 times (but in the past few weeks suggesting something has changed) and always after dropping from the large front chainring to the small one on a hill. Also rear gear had been in either 3 or 4th cog. The condition under which the issue occurs means a quick unclip and stop with no real opportunity to try see what has happened. Last time before dismounting I tried to pedal but couldn’t. Also could not back-pedal although the bike would freewheel a little. When I got off and looked, the cassette was free and normal.
I can’t replicate on the repair stand. I have stripped and lubed the free hub (but do that every 1000 miles to stop the Mavic howl) and that appears normal. The pawls are in fine order etc.
I am wondering if the rear derailleur is “bouncing” as the chain momentarily slackens as it drops onto the small front ring and could possibly be jamming against the cassette. But I can’t see any signs of this on the jockey Wheel or cage.
I am at a loss as what to check next. Any ideas folks?

 

[Deleted member 1258]

Could be chain suck?

 

[Deleted member 1258]

https://bikemagic.com/how-to/mountain-bike-maintenance/chain-suck.html

 

[confusedcyclist]

Recently I have experienced the cassette feeling to have locked up. It has only happened 3 times (but in the past few weeks suggesting something has changed) and always after dropping from the large front chainring to the small one on a hill.

Has the front derailleur slipped down or rotated? If so, the chain might be momentarily catching on the chain guide.
https://www.parktool.com/blog/repair-help/front-derailleur-adjustment, follow step 2 and 3.

 

[Yellow Saddle]

Could be chain suck?

My thoughts too.

OP, have a look on the chainstay, just next to the small chainring and see if there are any scrape marks in the paint. Chainsuck usually causes some damage here.

Also, a few nice photos of your chainrings, chain and rear set-up will help with diagnosis.

 

[Sillyoldman]

Thanks folks. Will try post some pictures. The FD is set up using a Campagnolo alignment tool so distance to big chain ring is ok and the cage is parallel to chainring.

 

[Sillyoldman]

Ok are these pictures ok? I can’t see any marks on the chain stay. Also I have a chain catcher in place and the chain has not forced itself past that.

 

[Yellow Saddle]

Ok are these pictures ok? I can’t see any marks on the chain stay. Also I have a chain catcher in place and the chain has not forced itself past that. View attachment 498836 View attachment 498836
View attachment 498836

View attachment 498836

View attachment 498837

View attachment 498837

Nice photos, but I need one more same, but with the chain on the large chainring and largest rear sprocket. I want to see how much your derailer moves forward in that gear. I suspect your chain is too short or, the derailer's capacity has been exceeded.

There's nothing wrong with your small chainring, so chainsuck is just about eliminated unless, the chain was very, very, very dirty when the incident happens.

 

[Sillyoldman]

Thanks Yellow Hammer. Chain is looked after so not dirty. There are no stiff links. I will take another picture and post it. I did think when I built this bike (my first attempt at doing that) that the chain looks a bit short on the big big combo- the rear derailleur looks quite horizontal) but as I never use that selection I thought it would be ok. I used the big big plus one link chain sizing method. Picture to follow.

 

[Sillyoldman]

 

[Sillyoldman]

Sorry Yellow Saddle got your name wrong. Apologies.

 

[Yellow Saddle]

Sorry Yellow Saddle got your name wrong. Apologies.

I quite like Hammer....it has a nice, delicate ring to it.

Anyway, your chain is too short. That derailer should bend forward no more than 45 degrees from the horizontal. Add a link and only then even try and diagnose further problems.

I suspect that when you downshift from that extreme cross-chain position (which you should never be in, in anyway), the jockey wheel derails from the chain and jams or, the spring action is so violent that it kinks the chain somewhere. Either way, start with a new link. Don't worry about putting a new link in an old chain, it'll be OK.

I didn't think you'll be guilty of an extremely dirty chain. That bike looks well loved.

 

[Sillyoldman]

Ok will do that but will have to replace the chain. Thanks a lot for your expertise.

 

[Ajax Bay]

At 1600 miles you've probably let the chain elongate too far to use a new chain on the cassette.
Buy a new chain, press out a link and use two Ultra-Links to extend the current chain. You then have a new chain waiting for when it slips (procure a new cassette for that moment too, to avoid days out of the saddle 'awaiting parts').

Potenza 11

If the extra link / longer chain fails to eliminate jamming episodes (definitely the first thing to do):
see page 35 in the user manual: https://www.campagnolo.com/US/en/Components/potenza_11_rear_derailleur
Look at your 'G' screw adjustment, given the 11-32 cassette is at the limit of the (medium cage) RD.

 

[Sillyoldman]

Thanks Ajax Bay. Measured chain and it’s still within Campagnolo spec. From that link (thanks for that) it quotes:
TWO DIFFERENT REAR DERAILLEURS
The Potenza 11 groupset will introduce the new 11-32 cassette.
To use it with all chain-rings combination is necessary to have a medium cage (72,5 mm) instead of the standard one (55 mm). So two derailleurs will be available at the same price.

I have the medium cage so that must be ok. So currently hoping the extra link is the key.

thanks