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Ultegra RD-6870-GS Ghost Shifting
My rear Di2 derailleur started to ghost shift on cogs 2-3-4. With the chain on the big ring (50t) and smallest cog (11t) I verified the upper stop limit was correct, derailleur hanger straight and jockey wheels (guide pulleys) line up with the cog. Same with the larget cog. In crash mode the derailleur shifts to each cog (up and down) okay but not on the road when I put load on the cranks. Shifts and runs fine on the 11 cog and on cogs 5 through 32 on either the 34 or 50 chain ring. It doesn't matter if I shift from 5 to 4 or 1 to 2 ghost shifting occurs. Any ideas or is my one year old RD in need of replacment?
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11 comments
Since a lot of things have been eliminated, here's a less-likely option: is it really ghost shifting, or is the chain skipping a tooth on the rear? Sometimes when riding it's hard to tell the difference.
Check the entire chain for links that are bound up. Sometimes they will come off the top of the upper pulley, and especially on the smaller cogs will not bend back fast enough to make the corner, making the chain skip a link.
Good shout, I managed to bend a link in a chain while cycling around Horse Shoe Pass, with Di2 I will tend to shift under some load, and that gave me a stiff link. I had to replace with a Quick Link, it wouldn't free up.
Thank you AndyStow. A DA chain with less than 150 miles had 4 slightly snug links. Mounted a new DA chain and all shifts are fine.
Victory is mine!
I had the exact same problem with a brand new chain, after one long gravel ride, just a few weeks ago. Spent ages trying to fix the "ghost shifting" while I was riding via a barrel adjuster, before I figured it out.
Check the rear wheel and cassette for any movement. Thru-axles are not 100% reliable, check the integrity of the freehub (my DT-Swiss came unscrewed during wheel removal), check for bearing play. Cassettes can come loose if not torqued correctly (happened to fellow rider recently and eventually wedged the rear wheel).
My experience of Di2 is the shifting is rock solid, so if the shifting goes wrong it is more likely to be something leading to the cassette being misaligned, if it is not a hanger problem.
The other thing is - is the cassette worn? Do you ride hard in those gears, have you recently changed the chain but not the cassette? Did you allow the previous chain to get over-worn? Is it actually shifting or is it skipping?
Checked your cable paths, especially under the BB? Or could it have stretched slightly?
Di2 so no cable stretch, bent hanger is all I can think of. Still worth checking with an alignment tool, even if visually OK, can still be out enough to affect shifting.
Doh missed that section.
My money would be on a bent derailleur hanger - simple enough to check. With the bike in the stand, check it visually from the back, the cage should be perpendicular to the ground. Then check with a mech hanger tool, instructions available elsewhere but basically you bolt it in place of the derailleur and check distance at 0, 90, 180, 270 degrees, gently bending the hanger in the right direction until gap is consistent. You'll probably have to re-adjust the derailleur when you put it back on. There's a chance of course it can't be bent back, in which case it will need to be replaced, typically £20 and is a sacrificial part to protect the dropouts and stays.
Or just take it to a bike shop and drink their coffee while an expert makes the problem just go away.
Thanks. Being a long cage the first thing I did was check the straightness of the hanger.
You need to check it with a Park DAG alignment guage. You cannot check a hanger visually with your eyes. I'm a bike mechanic.