New chain skips under torque

[miklekrs]

Hi,
I have a good old trusty trek fx 7.5, only thing i had to do on it over the years is a new chain when i've bought it, everything worked flawlessly, with a bit of tweeks and adjustments here and there. i was running kmc z9 what i was shortened to the lenght of the old chain, worked fine in the last 4 years, but now it was stretched. So i ordered a new set of kmc x9-s and shortened to same lenght, but now every time i go uphill or i put some force on the pedals the chain jumps/skips on the casette for some reason, and i don't think i have done anything wrong. Is it possible that the chain is not compatible with the sram 9 gear casette? Nothing like this with the old one. When i sized the chain i pushed the old one close so i was not sized it longer but the difference would be only 1-2 links and i don't think it would make any difference really.
Thanks

 

[Animo]

Cassette might need changing too. They get like that if you run them too long with a worn chain.

 

[Paulus]

As above⬆️

 

[Spiderweb]

Most likely a new cassette is required. You can usually wear out 3 chains before a new cassette is required but if you leave the chains too long without replacing then you may only get 2.

 

[Webbo2]

Depending how many years “ is over the years” you might need new chain rings as well.

 

[ColinJ]

If you'd rather not buy and fit that new cassette and/or chainrings to fix the problem, you might be able to put the old chain back on and get a few more months use before the old chain itself starts slipping. I did that in the past when I couldn't afford to replace everything all at once, and made do while I saved up for the new parts.

It would be better to put the new parts on now though if you can afford them!

 

[miklekrs]

hmm, okay. Make sense. This is not a new fancy bike i can probably get the parts cheap off ebay. the hard bit is to find out what exactly i need to buy, as i had this bike for 5 years and i bought it 2nd hand, plus it has been sold for many years with small modifications. Not even sure if the sram cassette is the original. i guess i should find some numbers on the cassette? i had it apart a few years ago to grease the bearings.
thanks

 

[katiewlx]

so whats happening is the old chain was wearing, and the cassette and chain rings, possibly the jockey wheels too were wearing at the same time, and they kind of wear in unison as theyre connected obviously, but not necessarily at the same rate, and it depends at what point you catch the chain wear before you kind of hit the point of no return on the other components. and by that I mean you should be able to replace multiple chains, before the wear on the cassette & the wear to the chain rings becomes terminal, its not a complete replace every time.

but there are alot of factors in play like how regularly you clean the overall drive mechanism, as I think theres a point where if you never clean it and especially over winter with lots of wet roads and grit and stuff that it collects, the muck that ends up on your chain and the gear components acts as an accelerant to the wear, literally the wear can become exponential, its not always just linear.

Right so when you put the new chain on, it skips under load because your new chain isnt worn yet, but the other components are worn to some degree, but as I say they arent necessarily terminal, I usually find when I replace my chain it can take a couple of weeks or so till the chain settles into the rest of the drive train, and then its good, and you keep an eye on the chain wear and wear on the other bits, and its all good.

Now for sure you are dealing with worn components at this stage, thats why its skipping, but its not new chainset necessarily, it just means at some point you might have to.

 

[mickle]

Your chain became so worn out from use that it ruined one or more of the sprockets of your cassette. You may also have damaged one or more of your chain rings.

Unless you have a Campagnolo rear hub, you just need to source a cassette with the same number of sprockets. This is also an opportunity to tweak your gear ratios if you want, so long as you don't exceed the tooth difference capacity if your rear derailleur. If you never use your current lowest gear you could, potentially, fit a cassette with a smaller largest sprocket. This will give you a higher bottom gear, but give you more gears in the range you tend to use. If you currently have a 13t smallest sprocket, opting for a 12t or 11t would deliver a higher high gear. If in doubt, simply replace your old cassette with a new one with the same tooth numbers and it'll work as its creator intended.

Every 'Shimano compatible' cassette will work whether SRAM, Miche, Shimano or any of the many off brand cassettes you'll find on ebay.

 

[Andy in Germany]

As others have said, cassette needs changing too. We rarely swap chains for customers without swapping the cassette as well: usually we swap the chain wheel too.

 

[Sharky]

Don't discount using your LBS. At times when you are not sure what the replacement part is, or you may not have the tools, a trip to your local bike shop is a good option.

 

[Ajax Bay]

the hard bit is to find out what exactly i need to buy, . . . Not even sure if the sram cassette is the original. i guess i should find some numbers on the cassette?

You have a SRAM cassette. tis means your freehub is Shimano.
Count the number of sprockets - ?10 - this is the 'speed'
Count the number of teeth on the largest sprocket.
Easy to find a Shimano or SRAM cassette (doesn't matter) the right 'speed' with a large sprocket the same(within two).
Google of bike make/model suggests: Cassette Shimano HG62, 11-34, 10-speed
Fit. Ride on (with your new chain - it will not skip).

 

[Ming the Merciless]

Time for a new bike