UFIbikes

I recently bought a road bike with Di2. I've has a recurring problem with ghost shifting. Occasionally, when I hit a bump my chain shifts. It usually happens on the rear, but has happened on the front twice. Front is little to big. Back is usually up to a larger cog. I'm going to verify it's not me accidentally hitting the shifters by doing a ride completely on the drops. But has anyone else experienced this?

tempocyclist

Never. I've had 10, 11, and 12-speed Di2 equipped bikes and none of them have ever missed a shift or ghost shifted, and they've required very little maintenance.

Sounds like whoever you bought it from did something very ham-fisted when setting up the Di2 or potentially crashed the bike. Maybe a bent derailleur hanger, or a chain that's too long. Ghost shifting little-to-big chainring is very strange though!

Actually, are you sure the Di2 is not set up to synchro shift?

Psimet2001 

Honestly sounds like some basic mechanical stuff.
1. Check the chain, chainring for wear.
2. Your rear derailleur hanger needs alignment. Just align it and/or check the alignment.
3. Your chain is most likely not sized correctly (too long) or there is too little chain tension. This is basic setup stuff.

Go through the basics. Odds are this will solve your issue. If not then it could be all sorts of things. crank that is able to move in or out, cassette has play for a myriad of reasons, etc. It's basic foundational stuff. Make sure it's all good.

As for Di2 - just works better so if you're having problems then its a basic foundation issue that has changed.

UFIbikes

I bought the bike brand new, no crashes and not in synchro mode. Had the shifters and derailer warranty replaced. I've considered the chain, but the mechanics don't think it's an issue. But I'll bring it up again.

Iride01 

Keep taking it to the shop or a shop that is a authorized dealer for that brand of bike. Eventually the reps from the regional level and possibly Shimano themselves will get involved. A bike that doesn't work correctly from the start needs someone higher up than the shop people looking at it if they are puzzled about the solution.

Don't be too keen on fixing it yourself. If you mess something up then you might be left empty handed on getting support from the shop, the bike brand and Shimano.

Welcome to BF.

SoSmellyAir

Does a Di2 derailleur still use a return spring like its mechanical counterpart, such that the motor or servo only moves the derailleur in one direction (to a physically larger gear) and the return spring moves it in the opposite direction? If yes, what the OP describes sure sounds like an electrical short in the system. (Pardon my ignorance, I do not (yet) have a Di2 bike.)

chaadster

I’d put money on this being the answer. Di2 doesn’t “ghost shift,” c’mon…

Iride01 

You do know that depending on what version of Di2 you have and the range of your rear cassette, Di2 won't go into the 12 and 11 cog when in the small chain ring. Regardless of what shift mode you are in, Di2 will make the appropriate shifts to keep you out of those combos.

spelger

i have Di2 but have syncro shift disabled. does that shift on its own? maybe why i have it disabled.

Iride01 

spelger

It only shifts when you push the buttons. However it might be more than one shift. If in manual shift mode and you are in the large ring and the 12 or 11 cog then shift to the small ring, Di2 will shift the rear to get out of the 11 or 12 tooth cogs. Depending on the Di2 version and the range of the rear cassette. I think if you have a 11-26 it will let you go into the 12 and 11 cogs. So maybe that's the ghost shifting the OP is talking about.

Also, Di2 will shift multiple cogs on the rear with a button press if you hold it down. I think this can be disabled and also the timing can be changed too.

Why don't you use full synchro? I have used nothing else since about 3 or 4 months after getting Di2.

Polaris OBark

The "brain" is in the battery. If they went to the trouble to warranty-replace stuff, presumably this is a legitimate issue. They might need to warranty-replace the battery.

But if it is simply a matter of unexpected syncro-shift behavior, turn all that off and see if the problem goes away.

bettershifting.com is a great resource. Start here

spelger

i guess for the same reason why i drive a manual transmission '79. that aside, when i got the bike syncro was enabled, i just didn't like it. and i did give it a while because it took me a while to get the SW in order to change it only to realize i only had to press a button on the junction box. all a learning experience. i have to add these little notes on my phone like how to check for a battery because i seldom have to do it. Di2 is pretty robust.

Iride01 

Fully synchronized or half synchronize isn't like an automatic transmission. You still tell it when to shift. It just lets you not have to worry about when to do the chainring shifts and moving the rear up or down two or three cogs.

You only have to use the right shifter. You could program paddles on the left or FD shifter for something else if you wish.... I think.

PeteHski

For sure that could only ever happen if the front mech actually powered up and moved over to the big ring. Whatever happened when you went over a bump triggered a full front shift. Probably bumped your hand into accidentally triggering the shift. Rear ghost shifting could potentially occur with an indexing issue, but not the front jumping little to big ring.

spelger

i know its not the same. i like to have some control over my life, even if just a little.


maybe something going on in the shifter? i assume the shifter paddles are just attached to momentary switches with a de-bounce circuit in between it and the microprocessor. assume there is some spring thing pushing the paddle away from said switch? never taken one apart and hope never have the need.

MidTNBrad

I have 6800 series Di2 on my bike and once had a sticky right-side shifter. It still shifted and released but not as crisply as the left one. A few sprays of contact cleaner fixed it.

Iride01 

How are you not in control? You tell in when to shift to a higher or lower ratio. Or do you just need to be in control of everything?

Micro manager! <grin>

mschwett 

isn’t it in the RD now? the brain, I mean. I guess OP didn’t specify what groupset.

my money is on bumping the shifter with a hand. can’t imagine any other kind of ghost shift on the front derailleur. it’s hard to move the FD against the motor.

Polaris OBark

Yeah, I was thinking wired 11-speed. But I suspect that it must be in one of the 12-speed batteries still.

I suspect (as do others) that the "ghost-shifting" is unexpected normal behavior. That is why I suggested turning off syncro-shifting for diagnostic purposes. However, on my wife's bike, even with syncro turned off, it won't let you cross-chain between the small-small and small-penultimate small gears, but if you try that, and then up-shift the front, it will subsequently "ghost-shift" the rear.

Iride01 

Another thought on the ghost shifting might be that the OP has the versions of Di2 that has the buttons under the tops of the hoods and they've been enabled for shifting. If you don't know they are there you'd never tell it without stripping the hood back.

Mine are set to work my Garmin GPS. Sometimes a bump with my thumb resting on top of the hood and my screen changes.

JamK

I have this exact same problem, with a new bike and 12 speed. I have had one shifter and rear derailleur changed on warranty, but still have the problem. Did you ever get a fix?

Steve B.

It sounds like a synchro issue where the R derailer skips and changes cog, the system then senses there’s a better gear ratio available and shifts the front.

UFIbikes

JamK- I did figure out what the problem was. I was riding with my index finger along the brake. And at random times when I hit a bump my index finger would hit the shifter just enough that it shifted. I thought that could be a possibility early on but I thought I ruled it out. But when I really paid attention that's what it was.

JamK

Thanks for that. I had wondered about that but also thought I had ruled it out. There must be something odd about the 12 speed that this happens as I don’t have this issue with the 11 speed di2.