New chain skips under torque

[miklekrs]

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.

i haven't always used all the gears top to bottom, so clearly shouldn't skip on all of them?
Thanks

 

[mickle]

i haven't always used all the gears top to bottom, so clearly shouldn't skip on all of them?
Thanks

What's the question?

 

[Ajax Bay]

Fine - if the shifters have been replaced as well with 9sp ones (think unlikely), get a 9sp cassette (no spacer btw, in case there's one there 'left behind') either SRAM or Shimano - will make zero difference. Don't know how you can say the shifting is "smooth" and in the same breath say "1 gear doesn't always shift".

every time i go uphill or i put some force on the pedals the chain jumps/skips on the casette for some reason

I think you'll find that the chain when under 'some force' only skips on a few of the sprockets, normally the middle ones which are those which get most use. But whatever, you need a new cassette.

i have a 9 gear SRAM on it currently, so previous owner must have had it replaced at some point, front chain ring is also seem to be not the factory one. explains why 1 gear doesn't always shift unless held it lightly

Front chain ring irrelevant to the symptom described. Make and model of chainset? I wonder if you have a chainline misalignment.
Not certain what you mean about shifting: how many clicks do you get from the shifters? Nine?