Cube reaction chain slipping/jumping issue

[RichKris]

Hi guys. I'm new to the forum so hello from Devon.
I have a 2021 Cube Reaction HPA with a Bosch CX engine and a Haibike Hardnine 6 with a Yamaha engine.
On my Cube I recently noticed that while in gears 10 and 12 the chain started jumping/slipping. I did all the usual stuff like setting the gears up again which made no difference so took the wheel off after noticing slight play in the rear cassette. It has a Sram NX Eagle PG1230 cassette system and the first 4 cogs are fixed while the others go on individually. I took the cassette off and took it apart to give it a good clean. I then put it back on and tightened it up properly eliminating the play. On the stand the bike goes through all the gears smoothly and sounds good but when I take it out on the road, it's fine for the first 8 gears but now 9-12 are jumping/slipping. I scrutinized all the cogs of the cassette while it was off and they all seem good. I even took the bike to Halfords for their free health check and they also reckoned the cassette looks fine and the chain is also good. I'm now scratching my head trying to work out what's going on as I've done all the usual things. Does anyone more techy clued up then me have any ideas? Thanks in advance.

 

[steve_sordy]

Send a photo of the cassette please. Doesn't have to be off the bike. Keep the chain out of the shot.

 

[RichKris]

Send a photo of the cassette please. Doesn't have to be off the bike. Keep the chain out of the shot.

Thanks Steve. Are these any good?

 

[steve_sordy]

I'm assuming from your choice of shot that by gears 10-12, you mean the small ones.

I have blown up both pics and they are too blurred for me to see well what I'm looking for.

Any chance you could take closer shots, higher resolution and on a clean cassette?

 

[RichKris]

I'm assuming from your choice of shot that by gears 10-12, you mean the small ones.

I have blown up both pics and they are too blurred for me to see well what I'm looking for.

Any chance you could take closer shots, higher resolution and on a clean cassette?

OK I'll have to take the wheel off over the weekend if I've got time and totally degrease the cassette.

 

[steve_sordy]

OK I'll have to take the wheel off over the weekend if I've got time and totally degrease the cassette.

I know it's a pain, but it is never a bad thing to do and frequently a good thing!
Lookout for other stuff to do while you are at it. Like crap in the mech, loose mech hanger bolts. Ensure all bolts are torqued properly.

 

[Bummers]

How many miles have you covered on that chain & cassette?

 

[Sparkomatic]

Bent derailleur hanger possibly. A friend had a similar issue and a new hanger fixed it.

Looking at your pics it maybe doesn't look straight?

 

[steve_sordy]

@Sparkomatic has a good suggestion. 12-speed mechs are notoriously prone to damage, which is why I'm on my 3rd on my current bike. But impacts don't always result in a snapped mech, often the mech hanger gets bent. They are meant to be sacrificial, so bending is easy. When I say "bent" I don't mean at an easy to see angle, they often bend by just a few degrees. Not enough to notice but enough to affect the shifting. On my first 12-speed, I took impossible to resolve shifting problems into my LBS. They did a mech hanger alignment using a special tool; it took ten mins and was cheap to do, cost me a tenner. But after the third time I bought my own mech hanger alignment tool (£60) and did it myself. I have since used it enough times to more than pay for itself.

So, it could be a bent mech hanger!

 

[RichKris]

How many miles have you covered on that chain & cassette?

Just over 1300

 

[steve_sordy]

Looking more like a bent mech hanger and less like the gears!

 

[RichKris]

@Sparkomatic has a good suggestion. 12-speed mechs are notoriously prone to damage, which is why I'm on my 3rd on my current bike. But impacts don't always result in a snapped mech, often the mech hanger gets bent. They are meant to be sacrificial, so bending is easy. When I say "bent" I don't mean at an easy to see angle, they often bend by just a few degrees. Not enough to notice but enough to affect the shifting. On my first 12-speed, I took impossible to resolve shifting problems into my LBS. They did a mech hanger alignment using a special tool; it took ten mins and was cheap to do, cost me a tenner. But after the third time I bought my own mech hanger alignment tool (£60) and did it myself. I have since used it enough times to more than pay for itself.

So, it could be a bent mech hanger!

Yes I think you could both be right. I don't think there's an issue with the chain or cassette and a bent hanger did cross my mind earlier as the derailleur doesn't look like it hangs totally straight from the rear.

 

[Mikerb]

mmm.............if the hanger was bent you would not get reliable gear changes when the bike is on the stand..........and you said it was fine then but not when riding. If you bike was a full sus I would have said you possibly need to reset B tension since shock sag would be the difference between the 2 scenarios........ but of course that will not be the issue on a hardtail. The difference between the 2 scenarios is therefore the amount of pressure on the chain when riding as opposed to merely rotating the cranks on a stand. Regardless of Halfords opinion I would say after 1300 miles the cassette is worn. That would not be unusual especially if you mostly ride in those higher gears ( and it looks like you do in the photos you posted of the cassette.
Replace the cassette and chain.

 

[Spin]

I would be satisfied with 1300 miles from a chain and cassette and happily replace those items before fussing over anything else. Especially considering the skipping is happening in the smallest cogs where drivetrain wear will become evident first.
That said , finnicky 12 speed tuning can be frustrating which is why I upgraded to 10 speed.

 

[RichKris]

mmm.............if the hanger was bent you would not get reliable gear changes when the bike is on the stand..........and you said it was fine then but not when riding. If you bike was a full sus I would have said you possibly need to reset B tension since shock sag would be the difference between the 2 scenarios........ but of course that will not be the issue on a hardtail. The difference between the 2 scenarios is therefore the amount of pressure on the chain when riding as opposed to merely rotating the cranks on a stand. Regardless of Halfords opinion I would say after 1300 miles the cassette is worn. That would not be unusual especially if you mostly ride in those higher gears ( and it looks like you do in the photos you posted of the cassette.
Replace the cassette and chain.

Yes that makes sense Mike. I'll straighten the mech hanger first and if that's not helping I'll order a new cassette and chain.

 

[RichKris]

One thing I am puzzled about is that, when part of the lower cassette was loose it only slipped in gears 10 and 12 but after I tightened it up it then slipped in 9, 10 11 and 12.

 

[Bummers]

Just over 1300

Chain stretch been checked? You've had decent milage out of it!

 

[RichKris]

Chain stretch been checked? You've had decent milage out of it!

Yes been checked using the chain gauge and all good.