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6870 Di2 Rear Mech B-adjustment

bl0k3bl0k3 Posts: 12
Hi all,

My drivetrain has been sounding a bit noisy, despite the gears been trimmed perfectly so I thought I would have a play with the B-adjustment screw to see if I could fine tune the gap between jockey wheel/ cassette.

When I turned the screw I noticed that it was having zero effect on the position of the derailleur. In fact the ring which the screw rotates isn't actually in contact with the derailleur and the derailleur can swing considerably in both directions. I.e. it isn't bottomed out in either direction, therefore cannot be adjusted, it just hangs loose.

Has anyone comes across this? Normally I take care of this type of thing myself but I am stumped! There must be a simple answer...

Here are a few pictures, not sure if they wil help at all but just to show that the B-screw is engaged, while the derailleur does not contact the flat section of the rotating ring.





Posts

  • pilot_petepilot_pete Posts: 2,100
    You are following the correct procedure for adjusting it and not just turning it in any gear right? The picture shows the derailleurs in a ‘mid’ gear which is not the correct position to make a B screw adjustment. Download the dealer manual for your rear derailleur which shows and describes the correct method.

    PP
  • pilot_petepilot_pete Posts: 2,100
    edited May 2020
    Here you go https://si.shimano.com/pdfs/dm/DM-UL0001-03-ENG.pdf page 64, put it in the smallest chainring and largest sprocket, turn the crank backwards whilst adjusting the B screw to get the top pulley wheel as close to the big sprocket as possible without jamming the chain. Then put the chain in the smallest sprocket and do the same to make sure the chain isn’t getting jammed.


    PP
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