BoSoxYacht

for the last few weeks I've been having a problem with ghost shifting on my Ultegra equipped Pedal Force RS. I'm using a 12-25 cassette, KMC-XL10s chain, and Ultegra R der. When I'm riding in the middle cogs (14-15-16-17) the chain trys to pick up the next cog on it's own. No amount of adjustment will make it shift smoothly throughout the middle cogs (using either chainring).

Does this sound like it might be caused by a bent derailleur hanger or bent derailleur mounting bolt? when I removed the rear derailleur yesterday the bolt seemed to have a slight wobble to it(like a bent pedal spindle).

998

slightly worn stretched chain?

waterrockets 

You can put a long bolt through the hanger, and snug it up with a nut and washer to see pretty clearly if the hanger is bent.

How does it behave at the very smallest cog?

Get behind the bike and sight down the chainline. Look to see that your top pulley's teeth are in alignment with the current cog's teeth. If they're to the left (my guess), then you can turn the adjustment barrel on your derailleur to the right 1/4 turn and see if it's any better (that will move the pulley to the right).

Psimet2001 

Does sound like alignment - mainly because you say it's trying to pick up the next cog instead of just skipping on the current cog. Otherwise I'd say your chain/cassette are worn pretty bad.

To expand on what waterrockets posted: Put the chain in one of the gears it is skipping in and hold a plumb-line (string with weight on it) along the inner or outer plates on the section of chain that is on the cog. Check to see if the line lines up with the same location on the chain down on the bottom pulley on the RD (after it stops swinging). If not you have your answer.

On Your Right

I had that problem on medium grade hills on my steel bike in the middle gears. I took the bike to the bike shop on several occasions and they could not duplicate it. It always shifted perfectly on the stand. I even rode it alongside the mechanic to prove what was happening.

When I bought my CF frame and built it up with the old Ultegra Groupset, I had no more problems. The difference in stiffness is incredible. We finally deduced that it was "frame flex" causing the rear deraillier to guide the chain onto the other sprocket while under high loads.

I do weigh 228 so on a hill I generate e tremendous amount of torque.

waterrockets 

So the theory is that the frame was flexing enough to pull enough cable through the derailleur to partially shift?

Spin Cycle

I had the same problem, in fact sometimes it would successfully move to the next cog. I tried every possible adjustment and lubricated everything, but nothing worked. I finally got the answer from Sheldon Brown's website (see https://www.sheldonbrown.com/autoshift.html) - I lubricated the guide under the bottom bracket and like magic the problem went away immediately.

Brian Ratliff

This doesn't sound right. The derailleur should move with the rear triangle of the frame. Unless the frame had a broken chainstay, I cannot see how it can deflect so much as to throw the rear cogs significantly out of alignment relative to the rear derailleur.

Brian Ratliff

A binding derailleur cable. Bingo! I think we have a winner...

R900

+1, New cable!