Slack chain - bike with derailleur

Over the last few weeks the chain on my good bike has got noticably more slack in it. There's also a lot more chain slap than there used to be.

Any ideas what I need to look at to fix it?

The RD is about 5,000 or 6,000 miles old... but it's an Ultegra Di2 one which is otherwise working well.

Chain also done 5-6k ?

New chain time.

Nope. New-ish chain, not registering any stretch with an 11 speed chain-checker.

Too many links?

Check the pivot for the derailleur jockey cage. If this has gone tight, the spring on the jockey cage may not be strong enough to take up the slack in the chain.

I had the same . Take the cage apart clean the spiral spring and arm faces where all the gunge collects . Grease it up tension the spring (not easy) and it will be like new . Do the bearings while its off the bike as well.

Why are you on the summer bike in november ?

Cheers! Is there a LBS in Central/South London who's good at this kind of thing? Not sure I've got enough mechanical sympathy or tools to take a cage apart.

(My best bike is my winter bike! Spent more money on something that's perfectly suited to crappy weather because we get more of that than sunshine.)

Brixton Cycles always gets a recommendation

BC recommendation seconded.

Why are you on the summer bike in November?

He needs every advantage in the viciously competitive world of mid-week winter training rides

if you push the derailleur cage forward and let go, it should spring back with no resistance and with a bit of force.

if it springs back but a bit too slowly and with some resistance, that will likely be the cause of your loose chain.

it's usually just due to the spring being caked in crap.

best thing is to just clean out all the gunk with a brake cleaner or something which will take old grease out with it, give it a good clean up. this will restore the snappiness. then relube with spray grease or something suitable.

if thats not the problem, you may have too many links in the chain

Cheers. Will give that a go before spending money.

https://www.youtube.com/watch?v=aoQq7Wb3EP8

Are you staying me around the forum just to take the piss?

That's it, buddy. Just you wait until you see what I'm riding tomorrow! :-)

I saw an opportunity, I took it

I make no apologies