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Old 05-15-12, 07:43 AM   #1
nrgy
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Di2 dropping chain?

If anyone here is familiar with Di2, I could use some help. I have had my bike for about 4 months now and I LOVE it however, if I am in the big ring and come to a stop as soon as I start to pedal again the chain drops down to the small ring. I have taken it in to the lbs and they have done all the adjustments. They can't replicate it on the stand. I guess my question is, is this something I am causing or is it the equipment? I had 105 before and rarely dropped my chain. The bike store has only sold 3 Di2 equipped bikes, so they are new to this as well and they have tried to help. I would say this happens about 75% of the time. Any ideas?
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Old 05-15-12, 08:32 AM   #2
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Are you sure you're not accidentally hitting the front shift button while you're stopped or as you're starting?
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Old 05-15-12, 09:26 AM   #3
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Are you sure you're not accidentally hitting the front shift button while you're stopped or as you're starting?
I don't think so, but it is certainly possible. I am going to pay more attention tomorrow and see if that is it.
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Old 05-15-12, 01:58 PM   #4
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It knows you need a lower gear. Do not question it.

Alternatively, has your bike shop given it a test ride to recreate the problem? A lot of stuff happens on the road, but not the stand.
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Old 05-15-12, 02:13 PM   #5
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No, I don't think they have tried to ride it. I thought it was possibly from moving my pedal backwards as I start out, but I have stopped doing that and it will still drop down. I do probably need the lower gear, I just thought I needed to shift it myself to get to it. It has been so amazing other than this, that I feel guilty for even having a complaint at all....
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Old 05-15-12, 02:25 PM   #6
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Uh-oh, the machines are revolting earlier than expected...
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Old 05-15-12, 02:42 PM   #7
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Uh-oh, the machines are revolting earlier than expected...
Something to keep in mind.
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Old 05-15-12, 05:41 PM   #8
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I do probably need the lower gear, I just thought I needed to shift it myself to get to it. It has been so amazing other than this, that I feel guilty for even having a complaint at all....
IMO that's a feature, not a bug.
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Old 05-15-12, 07:14 PM   #9
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big ring and what cogs in the back? towards the larger ones? does the derailer physically move or the chain just falls?
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Old 05-15-12, 07:38 PM   #10
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I upgraded my Ultegra 6700 to Di2. I did the install and it was easy. The shifts have been flawless. The front derailleur shifts so fast and easy.
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Old 05-15-12, 09:37 PM   #11
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If anyone here is familiar with Di2,
You don't need a mechanic, you need an electrician.
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Old 05-15-12, 10:37 PM   #12
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I thought electronic shifting was supposed to be perfect and foolproof? Maybe the shop didn't properly seat the ends of the cable housing

Sorry I don't have any actual help to offer...
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Old 05-15-12, 10:46 PM   #13
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I thought electronic shifting was supposed to be perfect and foolproof?
It almost is, but fools are too ingenious.

Seriously, I'd suspect some kind of contact problem. Possibly when starting out you flex the lever body or something like that causing a signal to the FD. I don't know the wiring logic of Di2 so can't say whether you're looking at a normally open which is shorting, or a normally closed which is breaking contact.

If the dealer can't help or duplicate the issue, I'd call Shimano in California. They did a lot of Beta testing here in the USA, and someone there might already have encountered the problem.
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Last edited by FBinNY; 05-15-12 at 10:50 PM.
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Old 05-16-12, 01:43 AM   #14
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It almost is, but fools are too ingenious.
Man, I love this quote
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Old 05-16-12, 07:02 AM   #15
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Thanks for the suggestions. I am going on a 30 mile ride this morning so I will pay closer attention to what I am doing when it happens.
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Old 05-16-12, 07:29 AM   #16
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Could be the high limit screw on the FD is a bit too tight. Also could be the lateral alignment is not set up correctly.

If this happens when you start from a start, I'd assume that you are in the lower gears/larger cogs out back at the time. That crosschain type of situation could cause it, if you backpedal at all in one of the lower gears -- FD will auto-trim toward the inside, facillitating the unwanted downshift.

Could also be Shimano trying to retrain you with your shifting. When approaching a stop, instead of shifting into a lower gear out back, consider shifting into the small ring up front...
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Old 05-16-12, 02:40 PM   #17
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Could be the high limit screw on the FD is a bit too tight. Also could be the lateral alignment is not set up correctly.

If this happens when you start from a start, I'd assume that you are in the lower gears/larger cogs out back at the time. That crosschain type of situation could cause it, if you backpedal at all in one of the lower gears -- FD will auto-trim toward the inside, facillitating the unwanted downshift.

Could also be Shimano trying to retrain you with your shifting. When approaching a stop, instead of shifting into a lower gear out back, consider shifting into the small ring up front...

I think this is it! I figured it was operator error When it would drop, I was in the larger cogs (usually the second or third one down). If I am in the middle of the cassette it does not drop. Thanks for your help, I appreciate it.
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Old 05-17-12, 08:46 AM   #18
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big ring and what cogs in the back? towards the larger ones? does the derailer physically move or the chain just falls?
Good questions. Have we established that the FD is actually moving and performing an active shift. Or is the adjustment just so close that the extra torque from standing start causes it to slip down on its own?
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Old 05-17-12, 08:47 AM   #19
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I think this is it! I figured it was operator error When it would drop, I was in the larger cogs (usually the second or third one down). If I am in the middle of the cassette it does not drop. Thanks for your help, I appreciate it.
I stiil don't think it should shift on its own no matter where you have it (even big-big, God forbid).
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Old 05-17-12, 10:33 AM   #20
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Good questions. Have we established that the FD is actually moving and performing an active shift. Or is the adjustment just so close that the extra torque from standing start causes it to slip down on its own?
That's my question. Is the FD moving as though in response to a command to shift down? Or is the crankset effectively flexing, causing the chain to hit the FD cage and be pushed off of the large ring? Does the OP always push off with left and pedal with the right to start? Does this behavior happen when starting with the left foot?
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Old 05-17-12, 10:35 AM   #21
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That. Or electromagnetic interference. Sheesh - I don't even like indexed shifting that much.
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Old 05-17-12, 05:06 PM   #22
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Ok, I always push off with my right foot, remaining clipped in on the left. I think the FD actually moves very slightly but now I want to double check it. I do know that I am nowhere near the shift buttons, so it is not an accidental shift.

Last edited by nrgy; 05-17-12 at 05:07 PM. Reason: mispelling
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Old 05-17-12, 06:02 PM   #23
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the fd auto trims depending on where you are in the back and front chainrings. im guessing the fd trims too much due to a sloppy limit screw adjustment. also check that the support screw is mounted properly.

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