Di2 won't front shift down under load anymore

I’ve recently noticed a problem with the front shifting on my 2019 Giant TCR Advanced 0 equipped with a Di2 R8050 as it doesn’t shift down under “load”. It doesn’t seem to be “pushing” the chain far enough and I really have to freewheel for it to work. On the other hand it can shift up under load (even when standing on the pedals) and everything else works fine (including micro adjustments in the front when changing gears in the back) so it’s hard to understand what the problem might be.

Backtracking a bit, my chain got stuck prior to that and I noticed shortly thereafter that one link was bent. After removing it (had to remove two links in the end) the chain looked too short so I got a new one, a Shimano 105 11S chain but I can’t imagine not using an Ultegra chain would be a problem ? I’ve done the adjustments several times in the front and made sure the chain tension was at the lowest possible B screw setting on Small/Small and nothing seems to help.

Has anyone seen that problem before ? Thanks !

Check the front derailleur outer cage plate isn’t bowed out. You may also see scoring on the back of the drive side crank arm.

Thanks, I hadn’t noticed anything wrong there but I’ll take a closer look. It seems like the FD doesn’t have enough power/strength to push the chain down when it’s tight. When it’s not tight the movement is wide and pushes it easily.
It doesn’t look like the micro-adjustments of the FD on the small and large crank have any impact on the amplitude of the “push” when shifting.
Now I did go from a 52/36 to a 50/34 so maybe some the height would need to be adjusted. That’s not when the problem started though.

Anyone else with that problem and/or idea for a fix ? Thanks !

I always adjust the FD position when I switch between 50-34 and 53-38. If the FD is to high the contact point is further down the cage. This can lead to more flex and a less precis shifting.

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Yep, you should definitely reset FD position. Usual rule of thumb is to have about a 2mm gap between the FD and big ring. Try that and report back. Also the idea of shifting chainrings under load makes me nervous - I always ease off the power somewhat for fear of dropping the chain even though it’s a rarity.


Thanks, I’ll try that.
As for shifting under load, sure, it’s not something I’d normally do, it’s just that currently I need to freewheel completely to shift down so it’s a problem. It’s really annoying when a hill starts and you’re in S2 mode and at the “changing point” the back shifts down and the front stays on the big ring !
I only tested the shifting up under load (even standing on the pedals) to see if it was also a problem there and found that it isn’t.

With a mechanical FD, I’d see if the spring was working properly and cover everything in RT85. No idea about Di2, sorry. Covering electronics in RT85 might not be a good idea though.

Yes the spring came to mind since the movement is wide as it should be when there is no load and weak if under load. Not sure how to check the tension or increase it though. Maybe I could blast some air in there…

No harm in cleaning/lubing the spring (in situ), and lubing all pivot points too, but I think the height will be your issue. PS 2mm is the height of the underside of the derailluer above the top of the teeth of the big ring - realised I hadn’t made that very clear.

Thanks, so I have now been able to put my bike on my home trainer and do some better troubleshooting and the problem remains after adjusting the height of the FD. Even with zero load it sometimes (after micro-adjusting mostly) won’t shift but if I push it down manually it moves and then resumes operation, up or down. Still won’t shift down under load though. It seems to be some sort of mechanical problem, nothing “broken” probably but something that “gets in the way”. I’ll remove the chain tomorrow to take a close look at the FD spring and try to clean/lube the spring and pivot points too.
I’m surprised I’m apparently the only one to ever have had that problem though !

Sounds like something might be impairing movement, so a good clean and lube sounds needed. Maybe a new cable might be a good idea. Otherwise I’m all out of ideas!

sorry to hijack, could you show me which parts of the di2 front mech that can be lubed?

It’s your front derailleur cage, if they get bent too many times then it loses its strength and just flex’s out when under hard shifts. It basically just bows out and now the cage is too pliable. Unfortunately you need a complete new Di2 front derailleur. Even if you bend it back it won’t work, the metal is now too soft.

It happened to me 3 years ago with my ultegra Di2 front derailleur and I was totally stumped for a week or 2 until I figured it out.

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Thanks for sharing your experience with a similar problem that could explain what I’m seeing, shifts ok when freewheeling but not under load. So I went back to the bike (still on my HT) and I can’t say I see any flex in the actual cage, but it could be internal I suppose, where the cage is “connected” to the engine/spring.
On the other hand, in spite of my intensive lubing (with WD-40) of the various pivot points and springs after removing the FD completely yesterday, when I first tried to shift down in the front I heard the motor noise but there was no movement of the cage, after pushing it down once it resumed normal action. I didn’t try shifting under load this time but the movements were quite ample.
So yes, getting a new FD would seem to be the way to go, 200€ though to be able to shift under load :frowning: The bike is less than two years old but it seems like it might be hard to explain the problem and get them to swap it under reasonable delays…

@ 4ibanez - yeah there seems to be some kind of impairment or “weakness” of the motor, not sure what more I can do though. I did see a screw on the side of the FD though, to remove the cover maybe. Not sure what I would find in there that would explain the problem though.

If you try squeezing the cage and bending it in, it’ll usually work for a shift or 2 until it gets bent back out slightly and then you’ll be having the same issue. It took a long time to figure it out on my bike and I realized that when the front der gets shifted and the bike is stationary, each time you do that you weaken the front der cage and then it easily deforms and the material gets weak and pliable. I put a new front derailleur on and instantly the problem was gone, when I compared the new FD cage and my original used one, the new ones cage was much much firmer and stout. It was very hard to bend or manipulate.

Makes sense, might be something different for me though as I can’t detect any flex when squeezing the cage, good to know there is an (expensive) fix though. In your case it sounds like it wouldn’t shift at all anymore though after the 1/2 shifts you got by squeezing the cage ?

After letting it sit for a few hours I did some shifting and this time it wasn’t stuck. I’m recharging it now in case the lower level (50% according to my Garmin) could account for that “weakness” (probably not). If it does that might require another battery, hehe…still cheaper than an new FD.

So recharging didn’t change anything to my problem. After letting it sit overnight I also got no action at first from the FD, just the motor noise. After a couple of tries and without pushing it in, it kicked into action and worked okish, i.e. not shifting down under load. I’m going to try to live with it, after all that’s how you down-shift on a mechanical by easing up slightly on the cranks…Maybe someone will pass by with a fix (pulling apart the FD ?).

I’ll ping the place where I bought it to get their thoughts. Ideally they could see the problem and get the ok from Giant or Shimano to swap the FD directly without sending it in…wishful thinking most likely :wink:

The servo is likely toasted… unfortunately ultegra warranty is only 1 year. There’s a substantial reason to get Dura-Ace… a 2 yr warranty.

Sorry for the bad news, Doug

You might well be right, have you seen that happen before? I’ll be riding like this next week and see how it goes…

In France we have a 2 year legal warranty normally but I suppose they could wiggle out of it as “normal wear” or “you did something you shouldn’t have done”…