thingsthatgo

Hoping someone can help diagnose this. Either my chain is skipping on the cog, or the freehub is slipping.

I have a SRAM 10-speed 11-28 cassette on a Soul freehub (https://2013.bikesoul.com/s3-0/). There's about 1500 miles on the hub and about 4000 miles on the cassette. A couple of weeks ago I replaced the chain (old and new chains both SRAM, not sure which model #) because it was showing stretch (about 1/8" over 12"). The mechanic at my LBS agreed that there was not enough wear on the cassette to require replacement, so only the chain was replaced. Shortly after the chain was replaced, I started feeling a skipping/slipping feeling when under strong load - only when doing a strong standing start from a stop or near-stop, and only on the 16t cog. The slipping occurred equally while in either chainring up front. There has been occasional slipping on the 17t cog, but rarely.

My first thought was a mismatch between the wear on the chain and on the cog, but some things made me think it could be something else: (1) adjusting the derailleur indexing made no difference at all; (2) the problem went away completely when I put the bike in the trainer, which has the effect of clamping down the hub and cassette extra-strong; (3) the pawl retaining spring in the freehub has broken previously, producing the same kind of slippage (though not confined to one sprocket) - it was just replaced in February; (4) the cassette has only 4000 miles on it and the cog in question has no visible signs of major wear; (5) the chain spins as quietly as with a completely new drivetrain (the old chain spun noisily).

I took the bike back to the LBS, where the mechanic opened up the freehub and found the pawl-retaining spring intact and couldn't see anything else wrong. He also completely re-indexed the rear derailleur. The problem was unchanged.

Is this a mismatch between chain and sprocket wear? Something else? If the former, would it be OK to just replace the one sprocket, or could it cause new problems to have unevenly worn sprockets (I'm thinking no, since sprockets naturally wear unevenly due to uneven use, but I don't trust my intuition very much). It seems a shame to replace an entire cassette after only 4000 miles. I've always replaced chains more often than cassettes (breakage, etc.), and while it sometimes makes the drivetrain louder I've never seen such a pronounced problem before.

Any suggestions are very welcome. Thanks!

FBinNY 

OK, this is the classic new chain, old sprocket issue.

Of course it might not be, but that would mean that your freehub coincidentally developed an issue at the same time the chain was replaced. That's an awfully suspicious coincidence. Also, freehubs don't usually slip this way. Once they're engaged they tend to hold. Freehub slippage issues usually manifest as slippage when first engaging after coasting.

10:1 you need a new cassette, but don't blame your shop. They were simply trying you to save you dough because the only reliable way to know if a cassette is worn is if a new chain skips.

thingsthatgo

Thanks for your answer. That makes sense. Any possibility of replacing a single sprocket? I always thought sprockets (at least the smaller ones, not the machined large ones) could be bought individually so that you could customize cassettes, but after an internet search I'm thinking I was mistaken.

ThermionicScott 

You can buy them individually, but they add up quickly if you have to replace more than one: https://www.universalcycles.com/shopp...?category=1569

Next time, replace the chain at 12-1/16".

dsbrantjr

Measure your chain frequently using a steel rule and replace it when 12 links measure 12 1/16"; at 12 1/8" or more you will probably find that it has worn the cassette to the point where it will skip with a new chain, as you have noticed.

The days of bike shops having a "sprocket board" where you could choose individual sprockets for replacement or customization is long gone. You will need to replace the entire cassette.

FBinNY 

You may be able to find a single sprocket, but you'll likely find it priced at a "why bother" level. About the only ones I ever see available at a price that might justify a one only replacement is the outermost sprocket.

Also, before replacing the one worst sprocket, consider how it might compare with the rest. If you spend 90% of your time in a single gear, than replacing just that one might make sense. OTOH, of you spend 50% of your time in one gear and 40% on it's neighbor, than, you need to consider replacing both, and the economics start turning against you.