UKC

Hmmm. Fng bikes. Need constant nursing.

My chain has started to sag on the top between front chainset to rear cassette. I changed the chain which was getting worn but.....it's not that. I think it's the jockey wheel bearings being worn and sticking. If peddle backwards quick, you see this sagging of chain.

Thought I'd ask those in the know before I buy another new component that isn't the problem. Does this sound likely to be sticky jockeys?

I never knew cycling was this exciting

The derailleur's not bent?

Does it sag when you just coast? If so it's a sticky freehub.

If not then, i.e. just when peddling backwards, then yes it's sticky jockey wheels. Before buying new ones it's worth just stripping them down and giving them a good clean, they tend to collect muck quite a lot.

On more reasonably priced rear derailleurs the jockey wheels will just use plain bearings, there'll be a little metal cap on each side and under this a small section of metal tube with the jockey wheel body spinning on this. Give everything a good clear and degrease, then reassemble with a bit of wet chain lube or similar light oil in the bearing (I'd advise against grease, it'll just attract dirt).

More expensive derailleurs will have small cartridge bearings in the jockey wheels. You can carefully prize the seals off with a knife, if they're not too far gone then clean/degrease, pack with fresh grease and put the seals back on. The seals are easily damaged or bent, especially when taking them off, so be gentle with them.

If there's excessive play in the bearings (i.e. they wobble a lot) then it's time for new jockey wheels.

If it's a sticky freehub then remedying will depend on what hub you have. E2A, if it is this  it's worth popping the cassette off, sometimes stuff can get down between the cassette and drive side flange which stops the freehub spinning freely.

Also, if it still shifts and pedals ok then I wouldn't go mad with replacing parts. If it gets excessive then you might drop the chain occasionally but a little sagging is unlikely to cause major problems (unless you're worried about losing a few Watts)

Have you spun the jockey wheels by finger without chain and feel if they are sticking?

Personally I would be looking at derailleur out of alignment before the jockey wheels, or maybe chain ring/cassette wear/damage holding onto the chain a bit.

quick spray with WD 40 ?

If you do need to replace the JW, then I'm a big fan of Hope-Tech JWs (if your set up will take them):

https://www.hopetech.com/products/drivetrain/jockey-wheels/

Cheaper than replacement MTB SRAM JW. 

Bear in mind that on Shimano rear mechs, the top jockey wheel intentionally has a tiny bit of lateral play in it to help the chain line up on the gear.

Thankyou all 

Yeah....it's the free hub. Feels rough n sticky. It's a relatively new wheel that was discounted ....from Merlin. Hmmm....I'm getting the picture now.

Cleaning jockey wheels is easy - they're held in with an allen bolt.  Some have bearings, others don't....

Could just be the seals are a bit new and tight or the grease a bit thick. It's a fine balance with free hubs between getting things running freely and getting them sealed adequately. Most of the more "performance" road models I've used tend towards the quick feeling but poorly sealed whereas the MTB stuff goes for bigger springs in the pawls, thicker grease and better sealing.