Funny shifting with new 105

marin_maniac

Recently installed new 105, everything seems all tickty boo except for an odd shifting problem.

Whilst in the smallest sprocket on the cassette performing a full sweep of the shifter takes me up two cogs as supposed. From there performing another full sweep of the shifter, it wants to shift three cogs but only shifts two and the chain ends up rubbing on the next cog as theres not enough tension on the cable to get to the 3rd cog.

If you try and correct this by increasing or decreasing the cable tension, that messes up the single shifts.

Any suggestions?

Ben6899

It still sounds to me like it's a cable tension and indexing issue. Have you followed Shimano's guidance on setting optimal indexing?

marin_maniac

Ben6899 wrote:

It still sounds to me like it's a cable tension and indexing issue. Have you followed Shimano's guidance on setting optimal indexing?

I thought that initially. If tension is increased, you can get it to shift 3 sprockets, but by doing that shifting to a harder gear is cock eyed.

Decreasing tension to get rid of the '3rd sprocket' shift results in poor shifting to an easier gear.

Ben6899

Are all the cables inners and outers new or in good condition. From memory, Shimano recommends that optimal indexing is set when...

in smallest cassette sprocket, push the lever as if to shift to the next larger one, but not as far as the indexing click. The chain should be rubbing the next sprocket and making a noise... and then with the click, it shifts.

marin_maniac

Cables and outers are shimano brand spanking new

Ben6899

And the gear change behaves as I outlined above? Here's the Shimano tech doc:

http://techdocs.shimano.com/media/techd ... 603908.pdf

Section 5... slightly different to how I recalled, but similar principle.

djheaton321

This is quite possibly a problem with the limit screw on the mech and cable tension. I have had this problem before. Put the mech onto the smallest sprocket and disconnect the the cable entirely. Now use the limit screw to get the chain running as smoothly as possiible on the smallest sprocket. Reconnect the cable nice and tightly and set up the indexing as described in the manual.

keef66

How would the limit screw affect shifting in the middle of the cassette??

djheaton321

If it is slightly out at the bottom of the cassette, it can be a cumulative thing, there is some gearing effect between the lever actuation and the mech, ie they are not one to one. Anyway, if it is the same as the new ultegra, it is not indexing properly at the bottom end of the cassette anyway, one full sweep of the lever should take you up three sprockets, not two. For the indexing to work correctly, it needs to start from the right place with the right cable tension. As an aside, Campagnolo is very sensitive to this, Shimano less so and SRAM doesn't seem very sensitive at all, that may be due to the one to one actuation, though I don't know as I have never really thought about it.

marin_maniac

Why does my Ultegra shift two sprockets at a time, and the instructions for the 105 state that it should only shift two sprockets?

djheaton321

Sorry, misunderstood you, it is shifting correctly at the bottom of the range. Try what I suggested and see if that helps. The other possibility is that the gear hanger is not aligned properly.