I have a 2004 trek 4300, with a SRAM 850 rear cassette (8 cogs).
I recently got a new chain installed (the third one). The cassette is still the one that came with the bike.
The cassette has about 1900 miles, and the first 2 chains where changed after 850 miles each.
Some gears keep on skipping (particularly, the 5th, 6th and 7th) when I pedal hard enough.
I went to the shop where they put the new chain, and they told me the new chain needs to wear in order to work properly, at least about 100 miles. I didn't need that with my previous chain, so why should I need that now?
I have done about 100 or 150 miles on the new chain.
They told me my cassette is fine.
Is that real, or my cassette has too much wear, and I should get both new chain and cassette?