Wandering gears!
 

Hi,

The chain on my bike has the tendancy to 'wander' over the smallest 3 or 4 cassette cogs. That is, once changed it will suddenly change up/down irrespective of chain loading. Changes to the largest cogs in the cassette are rock solid. I have tried tweaking the trim on the handle bar changers to no avail and sometimes its fine. Just annoying and make changes to the smaller cogs much more tentative!!

The cassette is new and the chain is nearly new (gauge shows its ok). The gear change is precise and the chain does not skip or slip over any cogs. The bottom bracket creaks but has no appreciable left<->right play and the freewheel hub that mounts the cassette only has slight play. The (sora hg9 speed) derailleur does have some 'slop' in the cage that houses the jockey wheels. That said, the derailleur and freewheel hub have about the same movement as my wifes new bike drive change components

I'm sure if I brought new chain, derailleur, cassette and freewheel hub the problem would go way! However, I'd welcome some advice in narrowing down the issue to the right component 🙂

Many thanks

Nick

Did you replace cables? Get derailleur hanger aligned?

Yes, cable is Teflon coated and really smooth in operation.
Err, not sure about hanger alignment? It's a cast Ali bracket that's bolted onto the frame in a fixed recess position.

Thanks for replying 👍

The derailleur hanger can be knocked out of line fairly easily. There is a tool designed to check alignment and correct it if necessary. By the way, the term freewheel and cassette do not refer to the same bicycle component. You can have one or the other. Using both terms is confusing for readers of your question

Before throwing more $ at this bike I would suggest letting someone with more experience have a look at it. Not because the bike isn't worth much but more to the hope of only replacing/fixing what's wrong and not blindly buy and replace otherwise well working parts. Andy

there's nothing "fixed" about it.

​​​​​​

assuming 9 speed indexed.

hanger alignment critical

overall sounds like rear derailler adjustment issues....

https://www.parktool.com/en-us/blog/...eur-adjustment

Good advice. But let me try to give you a crash course to figuring it out for yourself.

• Put the bike on a workstand
• Assure yourself that the chain and cassette cogs aren't excessively worn. There are tools and hundreds of pages of advice for this.
• Duplicate the problem that is happening on the road on the workstand.
• When you find it, slow it down so you can observe everything that happens. Does it happen on the same cogs? Does it happen on the same teeth of the same cogs? Doee it happen on the same spot on the chain?
• Remove the offending component(s), examine and determine if it (they) should be replaced or repaired.

In this instance, "fixed" means machined into the dropout, i'd speculate.

do you have the correct spacers/spacing?

start with adding more tension to the RD cable (with barrel adjuster / whatever)

( more if / than you’ve already done )

Nick,
When this "ghost shifting" has happened on my bikes, it's always been the derailleur hangar is out of alignment. I'd take it to a bike shop, they've fixed this issue a zillion times.

If you have a replaceable alloy RD hanger, these are generally designed to bend if the RD receives a significant impact. This is so that the hanger - and not the frame or the RD - takes all or the majority of any damage resulting from the impact.

After the hanger bends, your RD is no longer properly aligned and rear shifting suffers.

With the proper tool, the hanger can often - but not always - be straightened and the RD realigned. If it can't be straightened enough, or if it cracks, it needs to be replaced. (Replacing it and keeping the old one for a spare after having both aligned is IMO the best option. Unfortunately, they're often very frame-specific and can be difficult to find, so that's not always an option.)

Without the proper tool, it's rather difficult if not nearly impossible to align the RD hanger if bent.

If you can't find another problem causing the issue, the advice above to have your RD alignment checked is in order. It may well still be in order if you find another problem and have fixed that, but in that case at least you'll have preempted a future issue by fixing the other problem.

Best of luck.

If it's not the derailer alignment, make sure the cassette lockring is tight. Dumb mechanic (me) put on a new cassette before a century and didn't tighten it down enough. 60 miles into the ride I had the symptoms you described. Banged the lockring back on (rock + nail) which got me to the next sag stop where a good mechanic (not me) tightenend it enough to last several thousand miles, until the cassette was worn out.

Question for the OP- Can you be more specific as to how your wandering gears are acting. Specifically if you were to shift into the second smallest cog and make sure the cable tension is correct to center the guide pulley below that cog than go ride the bike with no more shifting would the gears still wander? This is an important detail that helps separate shift indexing from other possible issues. A bent der hanger won't cause wandering if the system was "corrected" for one cog and there's no more shifting tried.

Or does the wandering only happen after trying to shift to another cog? Besides der hanger alignment cable/casing friction and cable condition inside the lever are two very common reasons to have crappy shifting. Andy

Its fine in the workstand, so nothing obviously wrong. Gears change crisply up/down and dont wander or skip. It seems to be induced by the loadings on the chain.

Sounds familiar to me to, on a previous occasion!!

Excellent idea, Thank you

Thanks for the collective feeling that its something to do with the hangar/angle of the derailler.

I have had a much closer look and noticed that the lowest jockey wheel (closest to the road) in the derailler cage appears to have a slight 'twist' in it. The chain does not run centrally and leaves/enters this jockey wheel at an angle. The main body of the derailler appears to be true.

I will explore further......

Also check for a slight wobble on the axle and adjust the cones if needed. Sideway movement of the wheel could be a cause of this.

The smallest cogs are the furthest from the jockey pulley and have the least amount of derailleur spring tension. So as springs age and dirt/damage accumulate in the parallelogram pivots, upshifting can go to hell on the smallest cogs.

Spray lube the derailleur out, check for smooth cable operation and adjust the B screw to run the jockey pulley as close to largest cog as possible.

"once changed it will suddenly change up/down irrespective of chain loading"

"It seems to be induced by the loadings on the chain."

Both are the OP's

I have a hard time reconciling these two statements. This is one of the reasons why I suggested a more experienced person to take a look. Cable friction issues can produce incomplete der movement (per index click) be it cable in casing or a frayed cable in shifter. This would also match the smaller cogs being where the problem is, as mentioned that's where the der parallelogram spring is at the lesser tension.

​​​​​​​But both a bent hanger and bad cables are easy to check for and quickly eliminate what is in good condition from the possible causes. Andy