Intermittent skipping / slipping?

dazzawazza Posts: 462
edited February 2010 in Workshop
Hi, I recently replaced the chain and cassette after it skipped / slipped a few times during my commute. It was a 9spd Ultegra 12-27 cassette, which had lasted just under 4000 miles with 2 different chains that were swapped at even intervals. The Ultegra Octalink 39.53 chainset has done the same 4000 miles.
A new 9spd Tiagra 11-25 cassette and KMC X9 chain have been installed with the existing Ultegra 6600 GS Medium Cage Derailleur. I worked out the chain length by wrapping the chain around largest cassette sprocket and largest chain ring and adding 2 links.
I cleaned and lubed all the components including cables and jockey wheels. All adjustments have been made and shifting appears smooth. There are no stiff links.

Now, after all this, the intermittent skipping / slipping continues and has become worse. I almost had a bad accident after losing control accelerating from the lights. It can happen unexpectedly when in a gear I had used without problems just minutes beforehand.
I’m thinking it’s the freehub, but don’t want to buy a new wheel without eliminating all other possibilities. The wheel is a cheap Jalco that came with the bike and isn’t worth fixing.
Is the Medium Cage Derailleur compatible with a 11-25 cassette and 39.53 chainset? Did I calculate the chain length incorrectly for this set-up?

Any other suggestions? Thanks


  • Your set-up appears fine but to check the chain length, put the chain on the large ring and the smallest rear sprocket. The pulley cage should now be perpendicular. I take it that the teeth on the chain-rings are fine with no "shark-tooth" profiles?
    If it is, then the Freehub would be my guess but check if the fault occurs in any particular combination.
  • nferrar
    nferrar Posts: 2,511
    Worth cleaning/lubing or replacing the gear cable to, sticky outer housing can sometimes cause jumping.