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Di2 rear mech issue

RossoCorso34RossoCorso34 Posts: 202
edited November 2017 in Workshop
I have a Cannondale SuperSix Evo and recently took off the stock Mavic Aksium wheels and replaced them with Cannondale Hollowgram wheels.

After this, the indexing was out and with a bit of investigation and a little knowledge I found that the rear mech is at +16 on the micro adjustment. When it's like this is hops and skips on the biggest cog on the rear mech. With the adjustment set to zero, it won't go to the smallest cog, it will ride over the top of the biggest cog and the Garmin reports it's in the a different gear to the one it's actually in.

So, it's as though the whole mech needs to be moved one cog away from the bike when the adjustment is at zero.

Where should I start to look at fixing this, I'm a bit of a novice with this, but should be able to follow instructions!

Posts

  • CiBCiB Posts: 6,098
    Sounds like you've got it too far across to start with. Drop into indexing mode and count the clicks all the way from one end to the other, to make sure you're at the end. It should be 31 steps unless they've changed it. Then click back to the halfway point, 15 clicks back. Drop out of indexing mode and check that it changes to the top & bottom without overshooting into the spokes or between cassette & frame - be careful obvs when you do this. If it needs any adjustment on the upper or lower limit screws do it carefully, a quarter turn at a time checking that the change has had just the right effect and no more. Then revisit the indexing. Starting from a known central point is the key.
  • At the zero point, it goes over the top ring. Won't get to the smallest one and reports the wrong gear to the Garmin.
  • CiBCiB Posts: 6,098
    That's the issue then - the cassette on the new wheel is further to the right than the old one, so the mech needs to be repositioned with slight changes to the limit screws. If it goes over the top in the highest gear it needs that limit winding in a bit to stop it doing that, and at the other end the high gear limit screw needs slacking off a bit to let the cage move far enough to drop the chain onto the smallest cog. As above, quarter turn then check, rinse & repeat till it's just so. Do this when you know the indexing is central at the 15th click in from either end.

    Do each one separately, get the top gear correctly positioned then do the other one, then go through the steps in post 2 to make sure it starts off from a central point in the adjustment steps. The system is blind in terms of 'knowing' what gear it's in. It works it out by reference to upper & lower limits, so you need that to be right. Once it is, it might not need fine indexing but it's so easy it's silly not to tbh.
  • Thanks for the replies, I will give it a go tomorrow and see if I can get it dialled in
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