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Shimano Di2 Compatibility (6870 vs 8050)

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Shimano Di2 Compatibility (6870 vs 8050)

Old 10-20-20, 04:50 PM
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WanderingAlbatr
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Shimano Di2 Compatibility (6870 vs 8050)

Recently purchased a 2014 TCR with 6870 and want to convert it to a full compact (50/34 and 11/34).

Is it possible to use the current Di2 rear derailleur (RD-8050-GS) without updating the 6870 firmware, battery, etc.? The 6870 long cage rear derailleur is limited to an 11/32 according to the Shimano specifications and I was hoping to go with an 11/34.
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Old 10-20-20, 08:51 PM
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I strongly suspect your 6870GS RD will handle the 11/34 without a hiccup and would try the 11-34 cassette FIRST before
making any other changes in the system. Shimano is persnickety about the RD/FD combos so if you wanted to use the
8050 you would almost certainly have to invest in the same series FD as well. OTOH the 6870 brifters will work fine
with the 8050 Di2 RD/FD. Some updating may be needed depending on the battery if you do go the 8050 route.
Changing the cranks to 50/34 is also a drop in replacement for the 6870 set up.
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Old 10-20-20, 09:33 PM
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I agree, it sounds like 6870GS RD can be adjusted to handle the 11/34.

I was looking at a compatibility chart for 11-speed road Di2 and it makes it sounds like you can mix derailers (6870 FD and 8050 RD). Am I reading the chart correctly? I am using an external battery.

bettershifting
dot
com/di2-compatibility-mix-ultegra-dura-ace-xtr-xt-and-grx-components/

BTW, what does the new battery add that is required for the 8050 RD? I have heard this might be a required change.
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Old 10-22-20, 01:35 PM
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Turns out that the leading issue is the older junction box (SM-EW67) is not compatible with the 8000 series derailleur (confirmed by the Shimano compatibility flowchart). If I upgraded to the SM-EW90-A/B and updated the firmware, it would work fine. It appears that the older external battery would not be an issue.

I think I am going to stick with the 6870 long cage derailleur and adjust it to run on the 11-34 cassette as SCH suggested.
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Old 10-25-20, 01:59 PM
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Yeah, you can mix derailleurs. - as long as you stay in the same 'category'. 'Road/GRX' is one category and 'MTB' is another .

The SM-EW67 junction is compatible with the 8000 series derailleurs (Page 3 of the compatibility charts: https://bike.shimano.com/content/dam....0.2-00-EN.pdf), but it is not compatible with any internal battery or BM-DN100 battery mount.

Also, you would definitely have to update the firmware on the SM-BMR1 / SM-BMR2 battery mount and possibly the junction itself before it would accept the newer hardware.

And yep, RD-6870 can definitely run 11-34, even if it is outside Shimano's listed spec.
(I have used an 11-34T at the Marmotte last year ).

If you ever want to upgrade that SM-EW67 to an SM-EW90-A, keep in mind that:
  • You need two new EW-SD50 wires (to both shift levers)
  • You can not charge external batteries through any Junction A (only the ext. battery charger)
  • You may not be able to update SM-BMR1 / SM-BMR2 battery mounts through the junction A / charger (may need a bike shop to do that)
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Old 11-01-20, 04:49 PM
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I am installing the new used 6870 long cage derailleur and it isn't shifting. The short cage derailleur still works fine.

When changing Di2 derailleurs is there anything special that has to be done? I tried doing the "Accident Recovery" mode and it still did not help. They are both Shimano 6870 series.

Does the rear derailleur need to be mounted and have chain tension to work? Right now it is just in my hand off the bike.

Is the derailleur potentially broken? It looks to be lightly used.
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Old 11-02-20, 01:57 AM
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At the very least, it should *try* to shift. When you press a shift button it should make a sound and try to move.

As far as I'm concerned, you should try:

(1) Connect it to a Windows computer and see whether or not the 6870-GS is detected (If you have a newer junction and not that SM-EW67)
or
(2) Take it to a bike shop and ask them to run diagnostics on it / update it.

It may just need a firmware update in order to work with the newer components. If the only newer component you have is that FD-R8050, you can try disconnecting that and then shift the RD.. see what happens.
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Old 11-02-20, 02:12 AM
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I recently got a reply from the derailleur seller and it turns out that he updated the firmware and I still have the original firmware version from 2014. Going to reach out to a LBS and see if they can perform the update.

Thanks for the feedback!
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Old 11-05-20, 01:44 PM
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My LBS was able to update the firmware for all of the components and now the derailleur is working correctly.

They charged $20, however it took them a few hours on and off because they had to update each component individually as opposed to a single system wide update (possible on newer systems).

Compact gearset here we come...
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Old 04-05-21, 05:54 PM
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Hello! Can I use a di2 Ultegra RD6870 front derailleur with di2 Ultegra RD8070 back derailleur? (shifters are 6070) Is it possible?

Thank you
Leo
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Old 04-06-21, 01:32 AM
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Yes, should be fine. You may have to update the firmware on the 6770 shifters though!
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