Argh! Ghost shifting is driving me crazy!

[texbike]

Ghost shifting. Who am I gonna call? Paceliners!

Alright, here's the situation - I just went through my Vamoots (with Dura Ace 7800) and added new cables/housing, chain, and cassette. Prior to doing the rebuild, the rear shifting was starting to get a bit sloppier - hence the desire to go through it and show it some love. Now the bike is randomly ghost shifting across the cassette when riding along at a constant tempo without applying significant torque to the pedals. I haven't been able to tune it out.

A few quick notes:

-New KMC 10 speed chain (with KMC quick link installed).
-New 7800 cassette.
-New cables/housing.
-Derailleur was thoroughly cleaned including jockey wheels.
-Limit screws properly set and derailleur adjusted in relation to the the cassette cogs.
-Barrel adjusters set to zero (all the way in) on both frame and derailleur.
-Chain was shifted to smallest cog and the slack taken out of the cable.
-Multiple adjustments made on the barrel adjusters - it shifts fine except for the ghost shifting
-Nothing has happened to the bike that would cause a bent derailleur hanger or derailleur.
-There doesn't appear to be a sticky link in the chain.
-I shortened the chain a link to see if too much chain could be the issue - no change.
-I tried a different cassette and also a different rear wheel - no difference.

So, I'm at a loss. Before I throw in the towel and take it to a LBS, I was wondering if you guys had any suggestions.

A couple of additional possibilities that I'm thinking:

-I installed the KMC chain the wrong way? Chains aren't unidirectional, are they?
-The jockey wheels are worn and could be causing the issue (the derailleur does have >20K miles on it)?
-The shifter itself is bad? It shifts fine outside of the ghost shifting, but it does have >20K miles on it.

Thoughts? Suggestions?

Worst case scenario, I do have a 7800 shifter and rear derailleur that are known to be good that could be tested on the bike to see if they're the issue.

Thanks!

Texbike

[mktng]

FHB bearings? edit: never mind. you tried two wheels

[parris]

Check the cable housings for any burr's that may be on the ends. Check that the ferrule's are fully seated on both the cable and in the adjusters. Check the bb cable guide for binding and/or movement. flush and relube the shift levers. Make sure the cassette didn't come loose on the freehub. If the 10 speed cassette is on an 11 speed wheel make sure the spacer's in place behind the cassette. Hope this helps.

[dave thompson]

Rear derailleur hanger tweaked a tad?

[David Kirk]

You say it "shifts across the cassette randomly" - are you saying it will shift more than one cog up or down from where you left it?

dave

[John H.]

7800 was a great group, but when it gets old it gets sloppy.

How many miles on shifters and/or rear derailleur? Is the rear derailleur sloppy when you wiggle it side to side?
Derailleur hanger straight?
Cable housing loops long enough? As they exit shifters and also the loop at the rear derailleur?
What kind of frame? Internal or external routing for cables?

[texbike]

Originally Posted by mktng

FHB bearings? edit: never mind. you tried two wheels

Thx for the suggestion!

Originally Posted by dave thompson

Rear derailleur hanger tweaked a tad?

I haven't checked it, but nothing has happened to the bike would cause an issue there that I'm aware of. However, it is something that will probably need to be checked if other attempts don't resolve the issue.

Originally Posted by parris

Check the cable housings for any burr's that may be on the ends. Check that the ferrule's are fully seated on both the cable and in the adjusters. Check the bb cable guide for binding and/or movement. flush and relube the shift levers. Make sure the cassette didn't come loose on the freehub. If the 10 speed cassette is on an 11 speed wheel make sure the spacer's in place behind the cassette. Hope this helps.

Thanks! Most of these have been addressed, but the ferrules, housing burs (I paid close attention to those, but maybe not good enough?), and cable guide haven't. I'll check those.

Originally Posted by David Kirk

You say it "shifts across the cassette randomly" - are you saying it will shift more than one cog up or down from where you left it?

dave

Hi Dave. The chain rides up on the cog that it is on and causes clicking and popping as it stays in that gear. It sounds like it's out of adjustment, but I haven't been able to tune it out with the limit screws or tightening of the barrel adjusters. When I mentioned "across" the cassette (poor wording) earlier, I meant that it was exhibiting the same behavior across a range of different gears/cogs. It seemed to be most prevalent across the the mid/lower portion of the cassette.

Thanks!

[texbike]

Originally Posted by John H.

7800 was a great group, but when it gets old it gets sloppy.

How many miles on shifters and/or rear derailleur? Is the rear derailleur sloppy when you wiggle it side to side?
Derailleur hanger straight?
Cable housing loops long enough? As they exit shifters and also the loop at the rear derailleur?
What kind of frame? Internal or external routing for cables?

The group has at LEAST 20K miles on it. Probably more like 25-30K. The cable length isn't out of the ordinary. I essentially replicated what was on the bike previously which worked fine for most of the 10 years since I first built it up.

[hokoman]

I will take a stab at it, I think it's a stiff link in your chain.

[cinco]

You didn't mention which bike. If der hanger isn't bent, is it possible that the hanger bolt(s) are loose?
Also, could your new cable have slipped from the tension bolt?

Andy in Houston

[ScottW]

The couple of times I've had ghost shifting on the RD, it was solved by increasing cable tension. This is particularly likely if cables have been recently replaced... after being in tension on the bike they can stretch a small amount compared to when they were brand new. Shimano manuals are usually detailed enough here but IIRC after setting high and low limit positions, you shift it to the smallest cog (actuate the shifter a few extra times to make sure the cable is fully released), then shift up the cassette to a middle gear (5th or 6th) and adjust cable tension such that the jockey wheels are dead nuts centered under the relevant sprocket. From there you may even need to back out the barrel adjuster (increase tension) slightly to keep it from ghosting in real riding conditions.

Originally Posted by texbike

The chain rides up on the cog that it is on and causes clicking and popping as it stays in that gear.

I'm interpreting this to mean you've got enough tension to shift the chain up to the next larger cog, but it's then not being held tensely enough to keep the chain dead centered on the cog, IOW the chain falls slightly back down the cassette.
Still guessing cable tension and/or possibly some slop in the shifter mechanism. I have not accumulated enough miles on a groupset to personally experience the latter.

[Dude]

are the der cable heads seated properly in the shifter?
Is the rest der cable routed correctly through the shifter?
pop off ferrules and make sure the der housing strands are all even.
reassembled der/jockey wheels incorrectly?
That's not how you set up a rear derailleur.
- rear der barrel adjusters should be about 2/3 of the way screwed in. thread frame barrel adjusters the same amount in so you can use them while riding.
- with no cable tension on rear der, set limit screws. High limit screw unscrew until you hear noise/jumping. screw in until no noise/jumping. - use your hand to push the der to low limit screw repeat limit screw thing.
- install cable. 1 click is one shift yada yada. don't "take slack out of cable" we're talking empirical feedback here, not based on feel.
- once limit screws and cable is set, pull with some pretty good force on teh cables to seat all the housing/ferrules etc.
- readjust cable tension as necessary.

Also, have you tried other *new* cassettes?
Is the b-screw too far in/out?
or you could take it to a shop and have another set of eyes on it.

[Black Dog]

Try a different chain from a different brand.

[muz]

My money is on the jockey wheels being swapped after disassembly.

[texbike]

Originally Posted by hokoman

I will take a stab at it, I think it's a stiff link in your chain.

That could be. I did look for that, but didn't find one that appeared to be overly stiff. However, while trying out a different wheel I stupidly contaminated my new chain with grit from the cassette on the other wheel. I'll need to remove the chain and flush it as a result and will check for a stiff link at that point.

Originally Posted by cinco

You didn't mention which bike. If der hanger isn't bent, is it possible that the hanger bolt(s) are loose?
Also, could your new cable have slipped from the tension bolt?

Andy in Houston

The bike is a Moots Vamoots from the early 2000s. It doesn't have a removable hanger. The cable is firmly anchored- checked and adjusted a couple of times.

Originally Posted by ScottW

The couple of times I've had ghost shifting on the RD, it was solved by increasing cable tension. This is particularly likely if cables have been recently replaced... after being in tension on the bike they can stretch a small amount compared to when they were brand new. Shimano manuals are usually detailed enough here but IIRC after setting high and low limit positions, you shift it to the smallest cog (actuate the shifter a few extra times to make sure the cable is fully released), then shift up the cassette to a middle gear (5th or 6th) and adjust cable tension such that the jockey wheels are dead nuts centered under the relevant sprocket. From there you may even need to back out the barrel adjuster (increase tension) slightly to keep it from ghosting in real riding conditions.


I'm interpreting this to mean you've got enough tension to shift the chain up to the next larger cog, but it's then not being held tensely enough to keep the chain dead centered on the cog, IOW the chain falls slightly back down the cassette.
Still guessing cable tension and/or possibly some slop in the shifter mechanism. I have not accumulated enough miles on a groupset to personally experience the latter.

Great. Thanks! Maybe I need to play with this a bit more.

Originally Posted by Black Dog

Try a different chain from a different brand.

A defective chain did cross my mind. KMC 10v chains tend to be well thought of, but I have both SRAM and Shimano 10v chains that could be tested.

Originally Posted by muz

My money is on the jockey wheels being swapped after disassembly.

I did give the derailleur a thorough cleaning, but didn't disassemble the cage, so the jockey wheels are in the same place that they were originally.

Originally Posted by Dude

are the der cable heads seated properly in the shifter?
Is the rest der cable routed correctly through the shifter?
pop off ferrules and make sure the der housing strands are all even.
reassembled der/jockey wheels incorrectly?
That's not how you set up a rear derailleur.
- rear der barrel adjusters should be about 2/3 of the way screwed in. thread frame barrel adjusters the same amount in so you can use them while riding.
- with no cable tension on rear der, set limit screws. High limit screw unscrew until you hear noise/jumping. screw in until no noise/jumping. - use your hand to push the der to low limit screw repeat limit screw thing.
- install cable. 1 click is one shift yada yada. don't "take slack out of cable" we're talking empirical feedback here, not based on feel.
- once limit screws and cable is set, pull with some pretty good force on teh cables to seat all the housing/ferrules etc.
- readjust cable tension as necessary.

Also, have you tried other *new* cassettes?
Is the b-screw too far in/out?
or you could take it to a shop and have another set of eyes on it.

This is all great info! Thank you for the guidance. I'll check these items and retry the setup as suggested. I've tried a 2nd new cassette AND a 3rd low-mileage cassette. The issue persisted across all 3 cassettes and 2 rear wheels tested. The B screw hasn't been adjusted, but it hasn't changed position from its previous setting that worked fine.

Thanks!

Texbike