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. Makes 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