Rattling cassette (SRAM, MTB, 12s, 11/50) - what's going on?

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 Dave Todd 21 Aug 2022

Here's a random question for the hive mind...

Just been out for a short, evening ride around Houndkirk / Blacka Moor with my son.  He's been mentioning a bit of a 'rattle' from somewhere around the back of the bike when riding fast over lumpy ground.  I could clearly hear this rattle as I rode behind him.  Assumed it was likely to be suspension pivot points.  Checked all pivots for tightness when we got home - all seems fine.  Checked every other bolt that I could - nothing amiss.

Finally gave the cassette a wobble and found that each individual cog can move on the freehub by around 5-10 degrees.  Largest 4(?) cogs are a single assembly, so they wobble as a block of 4.

Used my chain whip to remove the cassette and it seems that the metal teeth which interlock onto the freehub are a bit worn and misshapen - giving rise to the wobbling.

I've never seen this kind of wear / play before - I'm presuming a new cassette is in order.  Is this a 'thing' with 12s drivetrains?  The bike's 3 years old and hasn't been ridden excessively (no hint of wear on the teeth / chain interface).

Any thoughts?  Cheers!

Post edited at 22:56
 Mini Mansell 21 Aug 2022
In reply to Dave Todd:

ask the same question on "coggers" and your likely to get a dozen offers of assistance in Sheffield.|

but,  what hub is it?   if its. Hope Hub and your running Shimano HG then there should be a thin washer behind that cassette which takes up the wobble your mentioning.

OP Dave Todd 21 Aug 2022
In reply to Mini Mansell:

Thanks for the reply - not sure what the freehub is (2019 Spectral 5.0) but the freehub itself seems fine.  I've never previously seen cogs which can be rotated back and forwards relative to each other (seemingly due to wear on their 'inner' teeth).  Just wondered if anyone else has ever experienced this.

 Mini Mansell 21 Aug 2022
In reply to Dave Todd:

that model comes with. Sram. NX eagle groupset,

unfortunately thats the bottom of the range as far as sram is concerned,  generally used by OEM to keep prices down. and still offer eagle.

Without seeing it (i am sheff based) i would assume that the cassette at assembly was ever so slighy loose (quite common) and over time the keyways on the freehub have been literally eaten into,  or if your luckier, the cassette has just worn.

out of curiosity, have you put a chain checker accross the links?  how worn is the chain?

i get around 1800m per cassette.  (9 months ish) and  600m. per chain.

but,  look on FB for the group called "coggers".  almost 6000. mtb riders in the south yorkshire area.   if your not already a member,  join,  its a friendly place





 

Post edited at 23:35
 elsewhere 21 Aug 2022
In reply to Dave Todd:

Lock ring clamping cassette onto freehub was lose?

Hence cassette can move and wear on freehub. 

Post edited at 23:43
OP Dave Todd 21 Aug 2022
In reply to Mini Mansell:

> that model comes with. Sram. NX eagle groupset,

Correct, it's NX

> i would assume that the cassette at assembly was ever so slighy loose (quite common) and over time the keyways on the freehub have been literally eaten into,  or if your luckier, the cassette has just worn.

Agree - this is what I think's happened.  I've just never experienced this before in 40+ years of bike fettling, hence my surprise!

Quick visual check indicates cassette 'inner teeth' (do they have a name?) very worn (rather than freehub splines) so hopefully a new cassette will sort it out.  I have another Spectral also running 12s NX so will do a quick swap of cassette to confirm my suspicions before ordering a new cassette.

Thanks for your thoughts! 

OP Dave Todd 21 Aug 2022
In reply to elsewhere:

It didn't seem particularly loose when I attacked it with the chain whip, but I suspect it must have been loose enough for a 'little bit' of play to become lot of play over time!

 Sam W 22 Aug 2022
In reply to Dave Todd:

I've got a Halo wheel that is a nightmare for this problem.  Better quality aluminium freehub bodies have a steel insert in one of the splines to stop the cassette biting into them.

If your freehub body is aluminium, I think it's unlikely the (steel) splines on the cassette will have worn more than the aluminium, and you'll need a new freehub body.  If freehub body is steel, then replacing the cassette may fix the problem.

 Stenton 22 Aug 2022
In reply to Dave Todd:

When you say 5-10 degrees of wobble, to me it's not clear if you mean the cassette can rotate on the freehub 5-10 degrees or they are able to wobble 5-10 degrees in the 'vertical' plane of the chain. If it's the latter, probably your cassette/freehub combo requires a spacer which has been left out of the assembly (had this once after a bike shop service, they must have lost the spacer on removal.

OP Dave Todd 22 Aug 2022
In reply to Stenton:

Sorry - difficult to describe!  I mean that the cogs can be rotated forward and backward relative to each other (and relative to the freehub!) in the front-to-back axis of the bike - not the side-to-side axis of the bike.

I'll get a photo of the 'inner teeth' of a couple of cogs...give me few mins...

OP Dave Todd 22 Aug 2022
In reply to Dave Todd:

Here are a couple of photos - those 'inner teeth' look very worn and misshaped to me.


 ianstevens 22 Aug 2022
In reply to Dave Todd:

Yup - probably due to a loose lock ring and movement over time. New cassette and maybe a new free hub body is probably the best option. (And check your chain when you swap the cassette too!)

 magma 22 Aug 2022
In reply to Dave Todd:

some ideas here: https://www.reddit.com/r/bikewrench/comments/icm9oe/loose_nx_sram_eagle_12_...

new groupset is quite a bargain atm- thinking of getting one for when my sx wears out (soon by the sound of it)

https://www.wiggle.co.uk/sram-nx-eagle-dub-12-speed-groupset

OP Dave Todd 22 Aug 2022
In reply to magma:

Thanks - that video on the reddit link shows my problem perfectly.  I'm hoping that I can get away with just a new cassette (£70ish from CRC / Wiggle).

I started this thread because I've never seen this issue before - but it seems I'm not alone.

 magma 22 Aug 2022
In reply to Dave Todd:

like Stenton said, missing spacer most likely..

Post edited at 13:56
OP Dave Todd 22 Aug 2022
In reply to magma:

> like Stenton said, missing spacer most likely..

Hm, not sure about this.  There are spacers between all the cogs.  I'm leaning towards a combination of (a) loose locking ring when originally purchased and (b) lower quality NX rings - possibly with a bit of (c) thin cogs due to 12 speed being added to the mix!

Anyway - purchase of new cassette is required as a minimum, along with usual check for wear on chain (and possible replacement).

 magma 22 Aug 2022
In reply to Dave Todd:

missing spacer would be between the freehub and the cassette..

OP Dave Todd 22 Aug 2022
In reply to magma:

It's a possibility...

If I can be bothered to remove the cassette from the other Spectral then we may have a definitive answer.  I'll try to do it this evening and report back.


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