Hey guys, I have a problem with the RD shifting on my bike. I have been using these Di2 components for 12 months, I crashed and scraped the right STI & also the RD, both have worked fine for 6 months since this happened. Yesterday everything was fine and then suddenly the RD behaves erratically.

The problem is when I'm shifting with the RD occasionally it will shift up the cassette (towards the 25) even if I'm trying to shift down i.e 17 to 15, it literally does the opposite to what I'm asking When it does this it does one of two things, it either shifts up for a couple of gear shifts (when I'm shifting the opposite way) but continues to function OR it shifts it's way up to the 25 and becomes completely unresponsive.

The battery is 50% full, all connections look OK, cables look OK, it's a DA cassette & chain on a TCR Advanced frame.

I tried going through the setup instructions again, everything in the right place and behaving well then suddenly the problem happens again on the work-stand

Any help would be really appreciated, I am an experianced bike mechanic but this is beyond me

To add: I have the gears working great for about 20 sec of pedalling on the stand and then the miss shifts and it stays in the 25t. I have gone through the 'RD Saver Function' and it makes it's way through the cassette ok although shifting from the 25 to 11 is possibly a little quick, it takes 2 gears at a time where as from the 11-25 it goes smoothly one sprocket at a time. All looks ok, then it misbehaves again. Is there a setting I'm un-aware of or is this FUBAR?

ruds

Sounds like you have a short that is asking for downshifts.

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For certain parts stiffer is more important than lighter.

Where might this be? Do you think it would be in the harness/connections or is it possible that it's inside a component (shifter,RD)?

Thanks for your reply

Basically, with electrical problems it could be anywhere. It could even be any place along the wire. If there is a pinch in the wire the two wires could occasionally touch triggering a shift.

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For certain parts stiffer is more important than lighter.

Ah I thought that would be the case -For anyone reading this, Di2 has be faultless for a years solid riding- I don't want this to look like Di2's rubbish because it's not, just obviously very different when things go wrong...

I only have an internal harness as a spare because I was in the process of drilling my frame for it, I'll give that a go.

I appreciate the help mate

So, start buy using a new harness kit without fixing it to bike. If it persists, then it's in either end - rd or shifter.

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Don't be alarmed.

Can't believe I hadn't thought of that! I'll do it right now!

I would quickly remove the Di2 group.......mail it to me, and I will send you a 105 5600 group. Problem solved!

Good luck, hope the harness fix works for you!

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2012 Fuji Altamira SE - 6.42kg

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Ok, swapped the harness, no response from the RD at all. As I see it:
1) RD's got a intermittent short/problem
2) The handlebar harness has a intermittent short and I don't have a spare one to check it.

The problem with number 2 is that I can check the battery status by holding the right STI's buttons down so obviosly some signal gets through OK. Also I could adjust the gears fine both ways using the right STI.

The problem I think is in the RD.

Does the Di2 RD have a force sensor or something similar that stops it from shifting if it's physically blocked?

OK, in the time it took to write that, the RD worked for 5 shifts then stopped working again, I think its the culprit. I'll replace it asap and post an update. Cheers guys

This would make your job easier: http://techdocs.shimano.com/media/techd ... 676584.pdf

Like any proprietary bike tools, if you own the group, this is well worth having.

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Thanks Madcow, I'll get one ordered.

The RD has a small PCBA for the stepper motor, and given the symptoms I'd say its been damaged.

PCBA= Printed Circuit Board Assembly?

Thank you for the input guys, the speed on the responses and friendliness on this forum is 1st class

New RD on the way for tomorrow hopefully