Jim’s Tech Talk
By Jim Langley
This week I’m sharing a small adjustment that makes a world of difference in the shifting of Shimano Di2 electric rear derailleurs. Recently I ran into and fixed this issue for a couple of roadie friends. Which makes me think that not everyone understands this critical adjustment.
My theory is that the confusion comes from the natural assumption that rear derailleurs are all adjusted the same. And also from the instructions provided with the Di2 components, which I sometimes find awkwardly written, incomplete and confusing.
Plus, for every new version/model year of Di2 and different Shimano groups that use the electronic technology, there are changes in the components and the instructions. That creates confusion and misunderstanding.
To help, I’m going to explain the basic problem, the cause, and the solution.
The Basic Problem
If your Di2 rear derailleur has been adjusted incorrectly, you’ll be experiencing inconsistent shifting. Sometimes the chain will make the shift you want. Sometimes it won’t. And, sometimes your bike will “ghost” shift, meaning shift when you didn’t actually shift it – and didn’t want it to.
The Cause
From my experience fixing this problem, I believe it occurs mainly because whoever did the initial install of the rear derailleur adjusted it the way standard (not Di2 electric) derailleurs are adjusted. I can appreciate how this could happen, because visually, it does seem like the electric derailleur is designed to be setup exactly like manual rear derailleurs.
However, when it comes to setting the limit screws, there’s a small yet critical difference. On both electric and manual rear derailleurs there are limit screws that set the sweep or in/out travel of the derailleur. They are adjusted to ensure that the derailleur can move the chain far enough each way to reach all the cassette cogs, smallest to largest.
With manual derailleurs, these limit screws are adjusted so that they hit stops on the derailleur. When they hit the stops, it prevents the derailleur moving any further. It’s an important adjustment to get right. Even only a half turn off with the limit screw can mean the difference between the chain staying on the cog or coming off. And, if it overshifts and comes off it can cause a crash or, in the case of shifting into the spokes, serious wheel and frame damage.
The Solution
It turns out that Di2 derailleur limit screw adjustment is NOT always done the same way as it is on mechanical rear derailleurs. And, also that if you do adjust the screws as if you’re working on a standard derailleur, you might actually damage or ruin your Di2 rear derailleur.
The reason is that Di2 components are operated by electrical shifters, a brain and motors. And one of their most interesting and sophisticated functions is the ability to self trim to fine-tune shifts.
On a properly setup Di2 rear derailleur you can see this in action if you watch closely. It’s easiest to see when you are shifting from the second-smallest cog to the smallest. Continue watching for a bit after the shift is complete and you’ll see the derailleur move inward closer to the second-smallest cog a tiny amount (assuming the limit screw is adjusted correctly – otherwise you won’t see it). If it’s quiet where you’re doing this test, you might hear the auto trim, too.
Don’t Block the Auto-trim Di2 Feature
The reason my friends’ Di2 rear derailleurs were shifting strangely and ghost shifting, was because the limit screws were turned in too far. This results in them preventing the derailleur from overshifting slightly and then auto-trimming. Worse it can drain the battery because the derailleur continues trying to move further than it can.
To fix this is as easy as backing out the limit screw(s) until there’s clearance between it and the stop. Once you have a small gap, the Di2 derailleur will work correctly again and your electronic shifting perfection will return.
Before you work on yours, though, you should search for its manual online and read it. Because not all Di2 rear derailleurs are the same. On some, only the high gear limit screw is adjusted this way. On others both the low and high limit screws are.
Finding the Correct Instructions
One way to find the right manual is to use Shimano’s new Di2 for Dummies site, here: https://di2center.com/2019/08/24/di2-for-dummies-beginners-guide-to-di2/. On this resource there are links to Shimano manuals for some of their recent Di2 groups. If your Di2 is not listed, you should search on “Shimano Di2 Manual” adding the model number of your derailleur, which will bring up the results for your exact derailleur.
The screenshots below show the directions for a high and low gear limit screw adjustment to give you an idea what directions you need to find for your rear derailleur.
PLEASE NOTE, that you need to find and follow the correct instructions for your specific Di2 rear derailleur. The screenshots shown are just an example of what to look for, and also the warnings of what can go wrong if the adjustment is not done right.
Ride total: 9,438
Jim Langley is RBR’s Technical Editor. He has been a pro mechanic and cycling writer for more than 40 years. He’s the author of Your Home Bicycle Workshop in the RBR eBookstore. Check out his “cycling aficionado” website at http://www.jimlangley.net, his Q&A blog and updates at Twitter. Jim’s streak of consecutive cycling days has reached more than 8,000. Click to read Jim’s full bio.
Thanks for the link to Di2Center! If you spot any mistakes or room for improvement please let me know 😉
Oh yeah.. we’re not Shimano 😉
Thanks for reading the article and letting us know, Terry. Great service you’re providing. Thank you!
Jim
Not sure if I’m experiencing the same issue, I’m using the 1st gen 10 speed dura ace di2, whenever I change gear on my rear D, the gear just go back to the previous gear. My mech told me the di2 failed time to change the whole groupset. What are your thoughts?
It depends – does this happen in every gear, or only the first or last?
If it’s the former, does that mean you are stuck in one gear?
If this only happens in the first or last gears your limit bolts are probably too tight..
Either way, a Di2 system should not “go off” just by itself, other than the hardware failing or being bumped/hit (derailleur hanger, for example).
If your hardware is failing, they are correct that Dura Ace 7970 is not compatible with anything else… unfortunately. If you had 9070 you could’ve gotten away with just upgrading both derailleurs.
Its happening on every gear, unless I shift it a couple of times then sometimes it doesn’t shift back. I guess i have got no choice but to change the whole groupset. Just curious whats the lifespan of a whole Di2 groupset component ? Just cannot find it anywhere online about lifespan.
I generally trust bike shops – they are usually run by bike enthusiasts and like riding as much as you and I do :). If they say it’s gone and doing micro-adjust on the derailleur does not improve things (https://di2center.com/2019/04/25/how-to-micro-adjust-your-road-bike-di2-rear-derailleur/) then they may be right.
I’m not sure about the lifespan of Di2 components. The battery is said to last 300-500 full charge cycles, which is more than anyone should ever need. Still, components (and batteries) do fail, but I don’t have any statistics on that :}
I currently have seven bikes and only one, a Giant Trinity Time Trial bike, has the electronic shifting. In some 700+ races, and a lifetime total of 330,000 miles, I’ve never had the standard cable shifting fail. Maybe noisy for a bit but a quick adjustment and I’m back at it. I’ve had the Di2 fail several times in races. Once, it completely stopped shifting leaving me in a 54/17 for 12 miles of a 40k time trial because the software needed to be updated. I’ve had the battery die (even though it was charged within 30 days) and I’ve had a cable to the rear derailleur disconnect. Overall, I like it on my aero bars as the shifting is quick and convenient but I would never have it on my road bikes. Electronic shifting seems to have solved a problem that didn’t exist. The beauty of a bike is the simplicity in my opinion. I’ll stick with cables.
Thanks for sharing your Di2 review, Peter. Very helpful and interesting.
And, regarding “330,000 lifetime miles and 700 races” all I can think to say is WOW, just wow!! Congratulations!
Thanks again,
Jim
Just shows how old I am 😉
I’m wondering if the same advice holds for SRAM eTap. I just had it installed to help reduce thumb pain from arthritis that is aggravated by shifting, especially mechanical shifting on the right hand.
Thanks for the question, Jim. I have not worked on enough SRAM eTap systems to know if it’s the same for all of them, but the instruction on SRAM’s website explain that the limit screws should be set to hit the low and high gear stops. So that suggests that for the current eTap you don’t not have to worry about having a gap for the motor to self-trim. This link should open the instructions if you would like to see them: https://www.servicearchive.sram.com/sites/default/files/techdocs/95-7918-013-000_rev_b_etap_axs_systems_manual.pdf
Hope this helps and that you love your new eTap and it helps with your thumb pain.
Jim
Thanks so much. I too have Sram and wondered about the adjustment. While i don’t have to adjust now it’s great to have for the future.
Not sure if I’m experiencing the same issue, I’m using the 1st gen 10 speed dura ace di2, whenever I change gear on my rear D, the gear just go back to the previous gear. My mech told me the di2 failed time to change the whole groupset. What are your thoughts?
I have di2 from 2012. I’m looking to find out why my rear derailleur shifts intermittently. But the front shifts fine. What can I try to fix it?