RD Switching Problem I Just Don't Get It!

[redir]

I've been riding the same two wheels with 9-Speed 12x27 cassettes, Shimano Dura Ace, for the last year regularly switching between the Open Pro set and a Carbon Neuvation set depending on the ride or race. On my TT bike I was running an 11x23 and also another spare set with an 11x23 but I have not used those much since I'm not as strong as I used to be and also living in the mountains the 27 is nice.

So the 12x27's got a lot of use and the 11x23's not so much. Within one weak I broke two spokes, both the rear wheels of the ones running the 12x27's so I had to do some switching around. I put in one of my 12x23 wheels and the shifting was terrible. I had th RD stops set just right but I would click and it would struggle to shift so I would have to click down twice then back once to get to the right cog. So I change the cassette out to the 12x27 and it shifts perfect. Ok, I thought, must be the chain/cassette wear combination. The old chain on the old cassette works fine because they wear together. So I replaced the chain, nothing. Still works fine on the 12x27's (both of them BTW) but doesn't shift well on both of the 12x23's. I go to the shop and get the RD hanger straight. The mechanic said it was off a bit but is now well within spec.

Now the shifting is perfect, as it always was, on the 12x27's but on both the 12x23's it will NOT shift into the 16 tooth cog, the very middle of the cassette. So my question is... WTH is going on??? I have a back up RD that I will try out tonight to see if that's an issue otherwise I am completely stumped.

[FlashUNC]

Worn chain with a new-ish cassette is generally a recipe for bodging the cassette, in my experience. Couple of the cogs in the 12-23 might be toast.

[oldpotatoe]

I've been riding the same two wheels with 9-Speed 12x27 cassettes, Shimano Dura Ace, for the last year regularly switching between the Open Pro set and a Carbon Neuvation set depending on the ride or race. On my TT bike I was running an 11x23 and also another spare set with an 11x23 but I have not used those much since I'm not as strong as I used to be and also living in the mountains the 27 is nice.

So the 12x27's got a lot of use and the 11x23's not so much. Within one weak I broke two spokes, both the rear wheels of the ones running the 12x27's so I had to do some switching around. I put in one of my 12x23 wheels and the shifting was terrible. I had th RD stops set just right but I would click and it would struggle to shift so I would have to click down twice then back once to get to the right cog. So I change the cassette out to the 12x27 and it shifts perfect. Ok, I thought, must be the chain/cassette wear combination. The old chain on the old cassette works fine because they wear together. So I replaced the chain, nothing. Still works fine on the 12x27's (both of them BTW) but doesn't shift well on both of the 12x23's. I go to the shop and get the RD hanger straight. The mechanic said it was off a bit but is now well within spec.

Now the shifting is perfect, as it always was, on the 12x27's but on both the 12x23's it will NOT shift into the 16 tooth cog, the very middle of the cassette. So my question is... WTH is going on??? I have a back up RD that I will try out tonight to see if that's an issue otherwise I am completely stumped.

Are the 12-23 'Frankenstein cogs', created out of others or box-stock?

[redir]

Are the 12-23 'Frankenstein cogs', created out of others or box-stock?

No, one is a Dura-ace the Other is Ultegra and they both were bought new. The ramps seem to all match up. I guess it's possible that they have more wear than I thought but I really don't remember using them for anything other than racing at most two races a week over a period of about 3 seasons, maybe. And I'm sure a hand full of training rides but nothing like I put the 12x27's through. I get a new chain at the beginning of every season too.

I forgot to mention that I replaced the shift cables and housing too but that should only make shifting better. The only thing I did different, a new trick I learned, is to rout the RD cable through the brazeon on the left of the head tube and vice versa such that the cables flow better and don't rub the head tube raw. So the cable cross over each other in the middle of the down tube before routing through the bottom bracket cable guide. But I've done this to great sucess on all my bikes now and it still would not explain why it only happens on the 12x23's.

I should mention too that if I tighten the RD cable then it shifts down through all the cogs just fine but then shifting up is delayed.