I currently run an Ultegra 6870 Di2 mechanical disc brake system, with the older external battery. I have post mount frame with a flat mount fork (currently with a converter to PM). I wish to upgrade the brakes to hydraulic. I've seen the DA R9170 shifters for a good price - close enough to the new Ultegra ones to go for them instead. So now my questions.
1) I plan to use a flat mount brake on the front (I already have a suitable caliper) but will the levers also work with a post mount caliper on the rear?
2) Will the shifters perform a basic up and down shift without firmware upgrades and/or battery replacement? I'm not concerned by the additional semi sync shifting, hood buttons, BT etc for now.
3) Anyone want to buy 6870 Di2 shifters and TRP Hy/Rd calipers?  3
(I may keep the calipers for another bike).
Thanks in advance,


Canyon48 [999 posts] 6 months ago
1 like

I have no idea about electronic shifting but I know enough about hydraulic brakes.

Flat mount/post mount makes no difference to the levers needed, only the calliper.

BikeJon [210 posts] 6 months ago

Cool. Thanks very much. That's the main questions answered.
Worst case (I think) is I'll need a new battery for the electronics. But at least I'd have a neat internal one, so I'm not too concerned if that is the case.

kev-s [298 posts] 6 months ago

Ive had quite a bit of experince of using mixed di2 components and this is what i found


If all the di2 components dont have the same firmware version then they may not work

for example if they are a mix of firmware versions 4.1 or 4.2 etc.. then all should be fine but if one component is on say version 3.9 and others are on 4.1 then the groupset wont work

Problem i found was beacuse of this you couldnt update the whole groupset to the same version using the battery charger as it didnt reconise the component thats got version 3.9 on it

You have to connect the component with the 3.9 firmware directly to the pc using shimano's pce1 interface device, update the component, then reconnect it to the rest of the bike, then you can update the groupset as a whole


The way i found this out is i built a Ultegra di2 bike for someone, updated the firmware to the latest version using the battery charger, 4 months later the bike came back and he asked me to upgrade it to dura ace di2 and gave me just the front mech, rear mech and chainset


So after fitting i went to test it and none of it would work, checked the firmware and the dura ace components had version 3.7 firmware but the battery, junction box etc.. was on the latest, once i connected the rear mech and front mech induvidally to the pce1 device and they were updated to version 4.2 the whole groupset worked