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Help! Upgrading my Trek 1.5 to close ratio cassette

pow216pow216 Posts: 3
edited October 2008 in Workshop
I've decided to upgrade my Trek 1.5 Triple to a close ratio rear cassette. Before making any changes here was set up which was working fine:-
Tiagra Shifters (upgraded)
Tiagra Front Mech (upgraded)
Tiagra Rear Mech
SRAM PG950 12-26 9 speed rear cassette
SRAM PC 971 chain
Bontrager Sport 50/39/30 Chainset

I bought an Ultegra CS-6500 12-21 9-speed Rear Cassette but just can't get it to shift properly at all. I've adjusted the limit screws, the cable numerous times and the B-tension loads of times too. It's very reluctant to shift in either direction.

It just doesn't seem to want to work!

Does anyone know if my new combination should theoretically work? I thought all shimano 9-speed parts should work together OK?

I've just put the 12-26 SRAM cassette back on and it's shifting much better already.

The only thing I've not tried yet is to shorten the chain. Do I need to do this? Any other ideas?

Posts

  • mackdaddymackdaddy Posts: 310
    Did a similar thing with a similar set-up. Sorry this will be of no help, but I can't see any logical reason why it wouldn't work.
    Did you remove the chain when you fitted it? Check the difference, maybe by photgraphing the chain line, position and the deraiileur position in whatever gear you are on. Maybe by comparing you might be able to find the problem.
  • John.TJohn.T Posts: 3,698
    If all you have done is to fit the cassette then it should work OK. there should be no need to alter the limit screws as all they do is what they say. Limit the extent of travel for the mech cage. One thing you may need to adjust is the B pivot screw that buts on to the drop out. This controls how close the top jockey is to the cassette cogs. For a close ratio cassette this needs to be screwed out a bit to bring the jockey closer. do not screw it too far or it will fall out but you may need to take it until it has all the tension off. Do not shorten the chain. Shimano recomend that correct chain length is with the chain on the largest chain ring and the smallest cog the rear mech jockeys should be vertical. This is for all cassettes.
  • pow216pow216 Posts: 3
    Good point about the chain length, I remember reading that now you say it. So it should work then. It did seem to work best with the B screw fully out, but it was pretty bad.

    Think I'll get a spare wheel and try again.
  • John.TJohn.T Posts: 3,698
    Do the 12 to 15 work OK. They should be the same as your sram cassette. Which chainring is it worst on.
  • The shifting should be better, not worse. Smaller cog jumps.
  • John.TJohn.T Posts: 3,698
    It does not always follow. The chain does hook up better if the jump is larger. With modern ramped cogs there is not much difference but way back in the early 60s the Campag Gran Sport would not work on single tooth jumps. You had to go past and come back. Things have improved a lot since then.
  • You have a valid point... going from 11 to 12T is sometimes difficult. :?
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