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Di2 shifting issues

by Robert Rollins
Mon, Jul 24, 2023 11:29
3

I have an issue with the shifting of the di2 on my new bike, the chain will not stay in the biggest sprocket.  It will shift into the sprocket but drops down into the second sprocket after 5-10 seconds.  Has anyone else had this issue?

  

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mark1a | 9 months ago
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Couple of questions, is this the front or rear derailleur, and is it 11 or 12 speed?

If rear derailleur and 11 speed, it's possible the H limit screw is not set correctly. This would mean the shift is not completing and sending back an error, and then the shift backs out again. On Di2, you do this last as opposed to first as with cable shift.  You'll need to place it in micro-adjust mode. Put the rear in the smallest cog, and then change up to 5th. Hold down the junction box button, LED will go red. While turning the crank, use the RH shifter to move the rear mech (fractions of a mm at a time) closer to 4th, until it starts making a noise. Then tap it back down 2-3 times, it should be quiet. Hold down junction button until LED goes out. Now move the mech to the biggest cog, and then wind off the H screw until it is *just* touching the mech stopper. Move the mech down to 11th and repeat for the L screw. It's important that the screw is only just in contact, enough to stop the chain from falling off, but any tighter and you can have battery drainage because the system will stay awake as it thinks it's not finished the shift.

The above should sort out most Di2 rear shifting issues, and it goes without saying that it's easier in a workstand and probably worth checking the mech hanger alignment first. Also to reiterate, above is for 11 speed, I don't have experience of the newer 12 speed, but I would imagine the adjustment process is similar, the adjustment mode selection will be different as there's no junction box.

Or ignore all of above and take it to a bike shop, if it's a new bike that was bought online, it may benefit from a once over to check everything is up together. This may cost a few £££ but would be worth it for peace of mind. My LBS charges £60 for unboxing, building, setting up and safety-checking of bikes bought online elsewhere.

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Cugel replied to mark1a | 9 months ago
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Di2 is preset to various limits that can't easily be changed. One such limit is the distance the front cage can move outwards in pushing the chain on to the larger chainring. If the bike frame front derailleur mounting is too in-board on the frame, the front Di2 mech can't quite push out far enough to keep the chain on the big ring, especially when the chainline is not very straight because a larger rear cog is selected.

A similar problem can occur if the chainset  centre line is unusually far out from the frame centre line.

If the chain does actually get on to the big ring, this is because the Di2 front mech auto-operation pushes the front mech cage out further than it's eventual resting position. The chain will go on to the big ring but then the front mech "trims" by moving the front mech cage back a little bit towards the bike frame.

If you have a frame with this problem of a poor front mech mounting placement, the front mech trimming motion can sometimes push the chain back off the front ring again. The first thing to try is to use the wee screw to allow the Di2 front mech to go as far out as it can - but it may still not be enough. And you may also get chain-rub issues if it is.

***********

I bought a bike with Di2 (it was 42% off in the sale, man!) last year and had various problems with the Di2 shifting.  It's fernickity and, because automatic, can't be hand-trimmed by the rider pushing a bit on a mechnical lever connecting the mechs with bowden cables. 

When the Di2 is perfectly set up, it works very well indeed.  This means doing the process mentioned by Mr 1a but also making sure the gear hanger (for the rear mech) is perfetly vertical and the B screw set right.

I've also discovered that Di2 doesn't like non-Shimano cassettes very much, or those that are franken-cassettes made up by the rider from various Shimano cogs into non-standard cassettes. Di2 is very sensitive to everything it's expected to work with, even the alignment (and definitely the non-presence) of the wee ramps moulded into the rear cogs to help lift the chain from one cog to the next.

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matthewn5 replied to Cugel | 9 months ago
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Cugel wrote:

Di2 doesn't like non-Shimano cassettes very much,

Mmmmm... I've only ever used my 11 speed DA Di2 with Campag 11 speed cassettes (as I only had a Campag wheelset) and it's been flawless shifting from day 1.

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