Hello,

For the last few months I have been using a new Shimano 13-25 (10 speed) cassette with a first gen Sram Force derailleur. I was previously using a 12-25 cassette, and shifting was fine. Since first installing the 13-25 cassette, there has been a delay shifting into the outermost cog, which was annoying but not a big deal.
More recently, I installed a new chain (same brand as before, KMC) and now suddenly the bike refuses to shift into the outermost (13t) cog. No amount of fiddling with limit screws and cable tension fixes the problem. The derailleur itself moves over the outermost (13t) cog and beyond, but the chain just seems to get hung up on the adjacent (14t) cog and stays there . The bike shifts fine otherwise.

I have no idea why a new chain exacerbates the problem to the point that I can't even shift into the 13t cog. It seems to me there are two potential reasons for the problem, though maybe there are other potential causes.

(1) Either, Sram derailleurs are not designed to work with a 25-13 cassette since SRAM doesn't make such as cassette

or

(2) my derailleur is just worn out. My rear derailleur is far from new. Is it possible that the springs in the derailleur are so worn that it can't clear the outermost cog when it is a 13t. Its worth noting here that I tried a 12-25 cassette with the new chain and it shifts into the outermost position perfectly.

Any ideas what is the most likely problem here?