Chain slipping with new chain, cassette and jockey wheels

[Marchaugh]

I'm trying to help my brother fix his bike, it's Scott Hardtail and has a Deore XT rear mech.
The bike was new in Feb but has been heavily used and abused. Much to my annoyance it doesn't get cleaned that regularly.
He said his gears weren't working properly so I checked the 10 speed chain and it had 0.5% wear so told him to order a new one. The jockey wheels were also majorly worn so I told him to get new ones of them as well.
He got them both, but got shimano 105 jockey wheels not deore xt ones. I thought this probably wouldn't matter as they are both 10 speed.
However I fitted all this and the chain still slips. This happens in both chain rings when accelerating or under load. It doesn't feel like it's trying to shift up or down (the kind of problem you get from wrongly adjusted gears)
I told him to order a new cassette although I though it still looked OK.
Chain still slipped!!
I checked the mech hanger, that was out slightly but it didn't fix it.
I thought there could be a stiff chain link but couldn't seem to find one.
There is a very faint chunk, chunk sound at regular intervals when you pedal but it seems to be coming more than once every chain rotation.
I did wonder about the chain rings but when it slips it really seems like its coming from the back.
It seems to only slip in the higher gears (smaller sprockets)
I have attached pictures of the components.
I would be glad of anyone's ideas on ways to solve this mysterious problem

 

[straas]

That chainring looks well past its best.

0.5% isn't excessive chain wear, so shouldn't have caused the casette to wear

The three outlined areas look really worn.

 

[Marchaugh]

That chainring looks well past its best.

0.5% isn't excessive chain wear, so shouldn't have caused the casette to wear

The three outlined areas look really worn. View attachment 542097

Thanks for your reply. Yes I would agree the big chain ring does look worn but what puzzled me is that when it slips it feels like its slipping on the cassette not the chain rings. It also happens in both chain rings and the inner one still looks OK.

 

[iluvmybike]

If it was in a bad state then it might need a new cassette as well as the chain - there is wear in the front rings but imo doesn't seem too bad. Check also that the jockey wheels are right way around if they are shimano ones

 

[Spiderweb]

My chain was well past it’s best and felt to be ‘slipping’ so I replaced the chain and at the same time moved from a 27t to a 30t cassette so measured the chain against the old one and added a link. My new chain slipped even more than before! It looked to be sagging slightly when in little/little.
I removed 2 links and it has been fine, I bought the bike second hand so maybe the old chain was always a little too long and started slipping when it had stretched.
So worth checking chain length maybe?

 

[Marchaugh]

My chain was well past it’s best and felt to be ‘slipping’ so I replaced the chain and at the same time moved from a 27t to a 30t cassette so measured the chain against the old one and added a link. My new chain slipped even more than before! It looked to be sagging slightly when in little/little.
I removed 2 links and it has been fine, I bought the bike second hand so maybe the old chain was always a little too long and started slipping when it had stretched.
So worth checking chain length maybe?

Good point, after a bit of looking around online I'm starting to think the same thing. I'll give it a go and update you.

 

[HobbesOnTour]

I'm far from a mechanic so take a large spoonful of salt...
I had similar with my old MTB commuter.
Chain slipping despite a new cassette/chain and eventually crankset.
It happened under load, but not every time and gradually became more common.
As it turned out the internals in the hub were giving way and the cassette would slip slightly.
Good luck!

 

[Marchaugh]

I'm far from a mechanic so take a large spoonful of salt...
I had similar with my old MTB commuter.
Chain slipping despite a new cassette/chain and eventually crankset.
It happened under load, but not every time and gradually became more common.
As it turned out the internals in the hub were giving way and the cassette would slip slightly.
Good luck!

Interesting, thanks. I don't think that is causing the issue but I will keep it in mind.

 

[HobbesOnTour]

Interesting, thanks. I don't think that is causing the issue but I will keep it in mind.

It shouldn't happen with a new hub but given you said cleaning etc. wasn't done I was thinking dodgy seals, mud and water might make a poor combination.

 

[Spiderweb]

What @HobbesOnTour said about the hub is definitely worth looking at too. I had a similar issue with another bike, a diagnosis and repair was beyond my mechanical capabilities so it went to the LBS and a new freehub solved the problem.

 

[PpPete]

Thanks for your reply. Yes I would agree the big chain ring does look worn but what puzzled me is that when it slips it feels like its slipping on the cassette not the chain rings. It also happens in both chain rings and the inner one still looks OK.

I've fooled myself into replacing chain & cassette un-necessarily when in fact it was the mostly less-than-visible (but over-used) middle chain-ring of a triple.
Was absolutely convinced the slippage was at the back, and all ready to spend money on new freehub when I spotted the chain-ring was fubar.

 

[wafter]

Check the derailleur tension too (B-screw) - I did similar on my old Giant - new chain on old cassette; OK for a bit then started slipping. New cassette, still slipping. Tweaked B-screw, all good. Probably shouldn't have given my mum my old cassette to use the sprockets as bird scarers on her allotment

 

[Marchaugh]

Thanks for all your suggestions. I swapped the wheel out last night but kept the same cassette. Still slipped. So I now believe it's the chain rings. After testing it with this theory in mind it did seem to be slipping at the front.
I've ordered some new ones so we'll see if that fixes it.

 

[Ajax Bay]

The feel of skating you get with a chain ring that merits replacement is very very similar to that you get when the chain has elongated too far for the cassette to 'manage'.

 

[Marchaugh]

New chain rings have arrived, fitted them and problem solved!
Thanks for all the suggestions.