JAJ0404

I just changed my cassette for the first time. I went from a 12-25 to a 13-30, both shimano ultegra 9 speeds, and everything seemed to go smoothly. But when I tried to run through the gears, I could start at the smallest cog and move to the 2nd, 3rd, 4th and 5th, but it would not shift up to the 6th cog. It tries, it goes up on the cog, but won't stay. What could be causing this? The spacing between each cog looks to be the same, this is a 2 tooth jump - 19 to 21 - but the shift before it is 17 - 19 and it has no problem with that, so I don't have a clue what the problem is - - - ideas?

jeepr

either it needs adjusting or a tooth is bent. Does it go past the problem gear and work properly or won't go any farther?

JAJ0404

It won't go any farther.

JAJ0404

I can't see any teeth that look bent.

Al1943

Try going through the derailleur adjustment instructions found at www.parktool.com.

JAJ0404

Thanks guys, I'll try an adjustment. Thanks for the link.

dsbrantjr

JAJ0404: Is your chain long enough? You will need a few more links to go around the 30 tooth cog relative to the old 25 tooth one. The chain will need to be long enough to go around the big cog/big chainwheel combination to avoid damage. Even if you do not intend to use that combination (and you shouldn't) you might shift to it by mistake.

HillRider

Two possible explanations:

1. Inadequate chain length as noted above
2. The low limit screw is too tight and won't let the rear derailleur move in far enough. Even using the same model cassette by the same maker, there are minor variations in tolerances and slight derailleur adjustments are often needed when switching cassettes or freewheels.

greyghost_6

Well as HillRider mentioned it may be inadequate chain length or high and low limit screws. But you should also check to see if the rear derailleur can handle all 30 teeth. Unless it is a long cage rear, short cages usually handle only 27 teeth usually, but may still work. I would look into your rear derailleur's max cog in the back to see if it is compatible, and if it is then look into adjustments.

hybridbkrdr

I read if you change the cassette, you need to change the chain as well. I don't know what's the best way of putting it, but apparently they wear together so it's like they adapt to each other. So, if you change one, you need to change the other with it.