Shimano 6870 DI2 rear derailleur setting problem

gorjanc

I have a problem setting the 6870 DI2 rear derailleur to index properly.

I have to move the micro adjustment for rear derailleur completly towards the smallest sprocket for it to index OK. But even in this position the chain is skipping one sprocket higher for a moment when under load (pedaling uphil), and only when on small chainring and second and third largest sprocket, other gears work OK.

What could be the problem, is it possible that the rear derailleur is bent?

trailflow

You mean you need to click it all 16 steps across ? Are you shifting into the 5th cog first before going into the micro adjustment mode ?

Follow the 6870 RD set up guide pdf (page 52)
http://si.shimano.com/php/download.php?file=pdf/dm/DM-UL0001-00-ENG.pdf

First adjust the b-tension screw.

The micro adjustment mode is for centreing the chain and eliminating any clatter you hear whilst in the middle (5th largest cog) of the cassette. Once centred it should run silently across the cassette. You should only have to press the micro adjust 4 times to silence the chain.

Then you should adjust the limit stops. Which can be tricky because some over shift needs to be allowed at the higher end of the cassette (smallest cog). Its called overshift allowance. You need to shift to the smallest cog and adjust the high limit screw (top side stopper) to where the RD finally stopped. Then do 1 full turn of the screw outwards. When the RD operates it will overshift and automatically move back in line with the smallest cog after shifting.
At the other end of the cassette, if the low limit screw (low side stopper) is too tight against the stop it will drain the battery and effect shifting. So it also needs to be loosened off a very tiny bit.

The first thing i would do is start over

Reset the micro adjust to the centre. (16 steps each way. 33 positions)
Turn the high limit screw outwards.
Check that the derailleur hanger is tight and not bent.
Check the RD tight on the hanger.
Check the RD jockey wheel bolts are tight.
Check the cassette lockring is tight. Check the individual cogs are seated on the freehub properly. Also check if you have too many (or not enough) spacers behind the cassette. Check for anything lodged between the cogs.
Check the chain isn't to short or too long.
Check the chain for damaged links.
Check the wheel is seated in the drop outs properly.
Check the skewer is tight.

gorjanc

Hello thank you for your extensive answer.

Yes I have to do all 16 micro adjustments, for the gear box to function semi properly. If I put the micro adjustments back to the middle I can make the indexing work smoothly but It will not shift into lowest gear.

How would I know how many spacers should be behind the cassette I have Mavic crossone wheels. Otherwise the cassette looks OK and the wheel is seated properly.

BTW I have a 32-11 cassette and a medium cage on the RD.

trailflow

When you say lowest gear,do you mean the biggest cog (32) or smallest cog (11) ?

Remove the cassette and count how many spacers are behind it. Try removing one and retighten. The cassette should feel rock solid with no side to side play after tightening.

Whilst doing that check the wheel axle is tight and there is no play in the axle or freehub.

Double check the b-screw adjustment on the RD and that the upper jockey wheel isn't hitting the cassette teeth and preventing it from shifting.

rafletcher

trailflow wrote:

Are you shifting into the 5th cog first before going into the micro adjustment mode ?

Gorjanc - Did you do the above? There in no need to use the micro adjust anywhere else EXCEPT in the 5th cog up AFTER you have set upper and lower limits as described in the guide. The lower and upper positions are set with the limit screws.

Rightarmbad

Your answer should be obvious from your first post.
If the trouble is only on one of the chain rings then you can be pretty sure that your hanger is out of alignment.
That will also explain the settings being at the extreme end of range.

When a hanger is bent, as in a slight twist, as the cage swings to take up or release the extra chain, the derailleur cage is moving inwards and outwards and moving the chain in and out of alignment.
It is happening to a small extent just as you move across the cluster, but a much greater extent when you change chainrings and the cage makes a big angle change.
This explains why one chainring may be in adjustment, yet the other not.
It also explains why the problem shows up at one end of the movement.

If your hanger is straight, you set it in fifth gear and it will index perfectly across all gears and chainrings, if it does not, your hanger is bent.

geoffh73

Have you adjusted the limit screws on the rear mech at all?
Could be that the lower limit screw need slacking off a bit so it will drop into the bottom cog.
Geoff

rafletcher

Rightarmbad wrote:

Your answer should be obvious from your first post.
If the trouble is only on one of the chain rings then you can be pretty sure that your hanger is out of alignment.
That will also explain the settings being at the extreme end of range.

When a hanger is bent, as in a slight twist, as the cage swings to take up or release the extra chain, the derailleur cage is moving inwards and outwards and moving the chain in and out of alignment.
It is happening to a small extent just as you move across the cluster, but a much greater extent when you change chainrings and the cage makes a big angle change.
This explains why one chainring may be in adjustment, yet the other not.
It also explains why the problem shows up at one end of the movement.

If your hanger is straight, you set it in fifth gear and it will index perfectly across all gears and chainrings, if it does not, your hanger is bent.

What utter nonsense :shock:

gorjanc

Ok sorry for the late replay.
First when I said lowest gear I meant 11 cog.

I again tried to adjust RD to the middle of micro adjustment, then I made some more adjustments so that it worked nicley in the 5th gear (2-3 micro adjustments). I completely slackened the low limit, but the RD will not shift into smallest cog.

I took the cassette off and there are no spacers behind it. The cassette is otherwise completely solid on the free hub no movement.

I think the most likely is that RD or hanger is bent. Any advice how to check this, with naked eye they look OK.