Electronic & Hydraulic Shifting (Di2, Ui2, customisations)

Check your B-screw? Try and microadjust, see if it helps?

Have you checked the B screw adjustment? Poor shifting on the small cogs usually means the mech is too far away from the cassette.

(which can also be caused by the chain being too long)

The mech hanger doesn't appear bent

Yeah, but is it? Di2 just just suddenly shift different amounts so the only reasonable explanation is something has moved and the most likely culprit is usually the hanger (or loose cassette, or worn chain, but you addressed one of those issues).

I've never updated firmware on any of my Di2 and they all just work. If it was the extremity cogs I'd suggest your limit screws were off but because it's kinda in the middle of the cassette it does sound more like something is piss.

But the issue was not there before the chain was swapped. B-screws don't just undo by themselves. Also the issue is with the big cogs, not the small.

I'll take the rear derailleur off, inspect and clean everything including jockey wheels on my lunch. If not then I'll see if I can get it in at a local bike shop to check the hanger before my race on saturday

Hmm, so everything seems in good order, apart from maybe one thing. The best way that I can describe it is that there is a bit of "slop" in the derailleur itself. So I can manually push the derailleur a tiny bit closer to the frame than the current shift position - probably only 1 or 2 mm, but that'd be enough to throw the shift off.

I'm guessing a derailleur is not meant to be able to do this?

Any ideas what I can do to fix this, or is it new derailleur time?

I think that's by design isn't it. They overshift a little, which is why you have the limit screws. It's hard to tell without seeing it and comparing to one that's new.

Yeah, that's my challenge. I don't have any other di2 bikes to compare it to.

I'll see if I can ring a mate and have them test on theirs, or see if I can squeeze in at the LBS. If anyone on here has a di2 rear derailleur to hand and wouldn't mind checking if they're able to push the derailleur inboard toward the frame about 1mm I'd really appreciate it!

+1
If your di2 shifting gets a bit wonky, it's almost always a bent hanger. Once you have the indexing and limit screws set up properly they will always be good because there are no cables to stretch, the derailleur always shifts the same distance and the rear spacing/spacing between cogs doesn't change.

If a hanger alignment doesn't fix it the only other thing that causes issues is a gunked up/worn tension spring which will affect how your derailleur moves as you shift up and down the cassette. Easy to pull it apart to check and replace if needed.

Anyone knows whats inside a Junction B box?

It is my understanding that with the e-tube system all the brains is in the derailleurs, shifters, junction box A (bar end in my case), and battery (assumption from the fact that syncro shifting isnt compatible with the older batteries).

What I'm getting at, is it possible in theory to splice the cables where they'd meet at the bottom bracket, and solder/crimp all red cables in a bunch, and all black cables in a bunch?

This is not the desired end result of course, but the easiest way to get the idea across.

I think it is a dumb junction, yeah. But why wouldn't you use it, instead of creating a mess of soldered cables in the frame?

My frame wouldn't fit it internally. At the BB its an aluminum BSA insert in a carbon frame, no clear access around BB inside of the frame as the original internal gear cables are running down outside the BB housing to the plastic guide, see pic below.

Issue no1: I cant route the Di2 cable through the original hole to the front derailleur as its way too small so it'll have to go around the BB housing. Not a clean look. Theres a lot of material there, and most of it seems to be the aluminum insert but Im not sure if I'd drill that hole up to 5.5mm to guide it through.

Issue no2: From here, I could use the external junction box, but theres no way to run the cable to the rear derailleur internally, the alternative is to use the adhesive cable guide on the bottom of the chainstay. Again, ugly.

This is a frame that I bought 7-8 years ago, and its been repaired after some damage so I'm willing to experiment on it.

So then I found this:

Article on it

Its a long shot, but good thing is that at the cost of cutting a di2 cable and investing in the DIY needs (£20-ish?) I can make a proof of concept on basically any piece of plastic/carbon.

Heres the idea: The dummy connection would be laid out into/onto the paint of the BB shell with gold leaf. Think like a circuit board. A 3D printed connector (that also functions as the crimped end of a di2 cable with a standard di2 connector on the other end) would be glued on this with conductive adhesive and this would run up to the front.

These "painted" lines then would come up on the side of the BB and near the FD again it'd have the 3D printed crimp glued on it, ending in a cable to connect to FD. Same for RD, paint running on bottom of the chain stay. Note that the battery will be in the steerer, connected to one of the shifters, so it wont have to be taken into consideration at the B junction.

Once connectors are glued on and system is operating, time to nicely mask it around, and the whole thing of course would get the clear coat treatment. Extra layer on the one below the chain stay.

Ambitious? Very. Would the end result be super clean? Yes.

Seems like a nice winter DIY tinker project. Worst thing to happen is that I damage the paint on the bottom of a frame, which I dont care much about.

1 Attachment

Fine if you want to experiment. I'm not that excited by bodges these days. I want stuff 100% reliable. Since you're not too bothered re: the frame I'd be more likely to drill the BB shell to get the Junc B through it but then it wouldn't be as interesting as what you're doing. :)

I could use the external junction box, but theres no way to run the cable to the rear derailleur internally, the alternative is to use the adhesive cable guide on the bottom of the chainstay. Again, ugly.

I'd run internal down the downtube to the external junction and then adhesive guide down the inside of the chainstay. It's no more ugly than having a gear cable run there which you're presumably happy with. The junction will be hidden by the cranks and you won't notice any of it when you're riding

is the d-fly thingy still known to drain the battery a bit quicker than normal?

if the firmware is up to date then no

great.

can't believe i'm going to have to buy a £22 1.5cm wire for it.

you can borrow mine?

I had external cabling but wanted to put the battery in the seat tube. Allbeit mine is a Ti frame, I didn't have to drill the BB shell, I removed the screw you can see in the image but the hole was not big enough to get the cable connector through. Simply got a cable long enough to get to the top of the seat tube, cut it near to one end of the cable (3 or 4 inches from the connector) then threaded the cable through the screw hole, out of the bb shell and up the seat tube. Then soldered the cable back together and covered in heat shrink. As a BB30 BB I had to ensure I used a pressfit BB to prevent the cable rubbing on the spinning crank. The only external signs are the di2 cable sheaf running down the centre of the downtube and under the ds chainstay.

Mine has cable taped under the chainstay as the Kinesis has a solid yoke joining the driveside chainstay which has always annoyed me but the cable has not been an issue under there. The BB has a shield piece covering the spinning crank but that makes the cable a pretty tight fit with BSA30 cranks. My Rotor cranks are noisy bastards nowadays after years of abuse. I'd love to put on normal Shimano cranks which would give me room back for cables and shut up all the noise but then I'd lose my powermeter and if there's no watts there's no ride.

Thats an option. I'll have a look how much space I'd have because it will probably end up with my Praxis crankset (30mm spindle with BSA bb) so might be a tight fit. But I still need to figure out a way to route to the FD.

@PhilDAS has the right idea, thats my most realistic option. I think I'll experiment with the paint stuff and see how it works. This wont be a complete build before next spring so ive got time :)

At the same time if anyone's got any cables, BT-DN110 battery, or internal battery charger to sell, let me know :) Thing about the cables, I cant really find them being sold second hand so I assume they are really reliable and people do keep them through groupset upgrades.

Anyone knows whats inside a Junction B box?

In terms of electronics, nothing.

What I'm getting at, is it possible in theory to splice the cables where they'd meet at the bottom bracket, and solder/crimp all red cables in a bunch, and all black cables in a bunch?

Yes.

Issue no2: From here, I could use the external junction box, but theres no way to run the cable to the rear derailleur internally, the alternative is to use the adhesive cable guide on the bottom of the chainstay. Again, ugly.

This is what I did on Cycliste's BMC. It's actually very discreet and hidden away. It's not as though people generally go around looking at the bottom of people's bottom bracket shells a lot. And the black adhesive guide along the DS Chainstay is barely visible against the black carbon. It's not an elegant solution, but it works and doesn't look bad.

Anyone know where might have an 8070 snap ring in stock?

SD 300 wires are slightly smaller than sd50 and might be easier to run inside frames.
They can be connected to SD50 with adapters.

https://www.bike-discount.de/en/buy/shimano-di2-ew-sd300-ielectric-wire-959914