Cranks slipping, changed the chain and that made it worse?

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Ahhh, it's the cold wet months when commuting seems to take a much heavier toll on my bike and I spend a portion of every weekend outside looking at it, scratching my head and then learning some new piece of maintenance devilry.  I get better at it but round every corner there seems some new thing to learn and new tool to buy!

Yesterday I wanted to get to grips with the cranks slipping when I was in my highest gear and trying to put power through them.  An occasional, but persistent slippage like when you change gear, I'd noticed this occuring on my last two commutes.  I also wanted to adjust my brakes as they were getting very soggy.  So up on the stand it goes and presto, the chain stretch tool instantly tells me the chain is too stretched.  I'm excited as I hoped this was the solution, I'm also smug that I felt I knew what the issue was, had the tool to measure it and even had a spare chain sitting in a draw ready for just such an eventuality.

Fast forward a couple of hours and I've cleaned the casette and big cog, replaced the chain, spent a lifetime furtling my s*dding, bl**dy cantilever brakes ("all this is controlled by just this one nut", the park tools video states, "and this can be frustrating") and put everything back together.  I jump on and arghhh the slipping seems to have got worse, rather than intermittent it is now pretty much constant.  Still present only when in highest gears though and when putting power through the system.  I can't replicate it when the bike is on the stand.

So what is it?  I suspect that it's a worn casette.  I've replaced my chain but not my casette, and an inspection of the casette reveals lots of the teeth are worn and slightly deformed.  Hard to tell exactly as I think all the teeth are very specifically designed to be different shapes.

I've just order a new casette, a chain whip and a casette removal tool to add to my ever growing collection of bike hardware

Any wisdom UKC? Do I need to replace my chainring if I replace my casette?

Thanks for reading, was good to get that out of my system : )

 Enty 10 Oct 2021
In reply to Bobling:

How long have the chain rings, chain and casette been running together?

If it's a long time you'll need to replace the lot because just replacing one or the other will be a waste of time (and money)


 steveb2006 10 Oct 2021
In reply to Bobling:

You are almost certainly right about the need to replace the cassette as the teeth wear as the chain gets worn then slips badly with a new chain. It is worth changing the chain more regularly and getting a 'stretch' tool to test if the chain needs replacing (i.e before it wears the cassette). Cheap to replace the chain.

With any luck you may get away with the original chain rings as these tend to wear less, but in the worst case they'll need replacing too


 Ragingpossum 10 Oct 2021
In reply to Bobling:

All a question of how worn the cassette and chainring are. General guidance would be if you have run a very stretched chain for a while then chances are you need to change your cassette as well (from your description and experience whilst riding it sounds like this is the case). Your chain ring is a bit harder to tell but if the teeth have become more spike like / increasingly concave lines / fewer square tops then it can also be time to replace.

Your drivetrain is one of the places where monitoring and replacing the chain regularly can result in only rarely having to replace the rest of it. 

Good luck with the new cassette and enjoy the commuting!

In reply to Bobling:

Replacing a chain and finding it 'skips' or slips is the classic sign that the cassette is worn out. The fact that the teeth of the cassette actually 'look worn out' is unusual because I wouldn't expect it to get that bad before problems occur. If you've run a very worn out chain, for a long time, the chainring might need replacing but not necessarily as, being so much larger, it will resist wear a lot better than the cassette cogs.

Have a look at how the new chain sits in the teeth, a worn chain ring will have teeth that have thinned or flattened and the troughs will be too big for the chain to sit snugly and lock into the teeth.

 wercat 10 Oct 2021
In reply to Bobling:

Snap!  Identical experience yesterday, though I thought my cassette was still OK.  Not quite sure that I have enough clearance between the lowest run of the chain (as it leaves the derailleur) and the derailleur body on the lowest gear though.  That clearance is lowest in the highest gears.

Post edited at 09:52
 MikeSP 10 Oct 2021
In reply to Bobling:

Have you tried indexing the gears?

If the gears are working at one end of the cassette but getting worse as yo move to the other Its worth a go.

If its slightly out it can jump of the cog for a split second before falling back into the same gear.

 felt 10 Oct 2021
In reply to Bobling:

It's worth remembering that when Shimano introduced hyperglide cassettes that people returned new ones to the store because they thought that the uneven teeth were a sign of wear/damage rather than intentionally meaning to look like that.

In reply to Bobling:

Thanks all, good to hear that folk think my hypothesis could be correct and that the cassette needs replacing, and that the chain ring may but may not.   It's hard to know how long they have all been running together as I've been on my road bike for most of the summer and it's too far back in the mists of time.  I did get the whole thing serviced at a pretty high end bike shop in July but I guess replacing the cassette and chain weren't part of the service, in future I'll make sure I'm clear when that happens. 

The good news is that as my bike was U/S I couldn't go on the planned ride round the trails of Ashton Court with the biggest child this morning, so we went to the Avon Gorge instead and had fun pulling on rock in the New Quarry and then terrifying ourselves getting high up on the Easy Route in trainers with no rope! 

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