= FIXED = Calling all Mechanics - Jumping/Slipping gear

[LEE]

I just re-fitted a cassette to a wheel it has been on before.  Now I can't tweak the rear mech to stop the top-most gear (smallest sprocket) from jumping.  The chain is riding up the teeth and dropping back down repeatedly with a rattle/clunk.

Please Note:

- Chain has not been removed.
- Jockey Wheels have not been removed
- Everything is the same and running in same direction as before
- Cassette/chain combination has not been used elsewhere.  I took cassette off to clean it.
- All other sprockets run silently (this tells me chain and jockey wheels do not have a problem)
- Hi-Lo adjustment has no effect (I've adjusted it to both extremes until chain falls off or changes down a sprocket)
- It changes slickly every time and rides perfectly in all gears apart from the smallest sprocket.
- It doesn't require spacers
- Lock ring is fitted tightly
- Cassette has no play.

It has all the symptoms of fitting a worn sprocket from another bike's casstee but nothing has been changed apart from a clean in white spirit. It rides up and falls down the teeth 2 or 3 times a revolution but it isn't trying to change down or fall off, chain is set centrally on sprocket (see Hi-Lo adjustment)

Why does this one sprocket seem like it doesn't fit any more?

It's driving me mad and is totally unusable.  If all the other gears weren't so silent I'd have more of an idea what was wrong.

[mattc]

I had something rather like this, confused me for a while:

the smallest sprocket was on slightly crooked. You had to stare at it from the right angle to notice.

It wasn't my wheel, so I just gave it back rather than actually fixing it 

[Jurek]

It sounds unlikely that you've done any damage in the course of dismantling / re-assembling.

Without wanting to cast nasturtiums about your spannering abilities, I found this site gives a very good guide how to fine tune the rear deraillieur.

[LEE]

I had something rather like this, confused me for a while:

the smallest sprocket was on slightly crooked. You had to stare at it from the right angle to notice.

It wasn't my wheel, so I just gave it back rather than actually fixing it 

It's behaving EXACTLY like a crooked sprocket would behave but is seems fine when I spin the cassette

[mattc]

If it quacks like a duck ...

[Von Broad]

Have you had it on a bike stand [or a bit of rope hung from hooks attached to the ceiling joists, in my case], and given it a good visual.

You should be able to see what's going on. Use a torch as well. What's driving you mad won't be invisible.

[inc]

You could try a bit more tension on the cage which is the screw at the top of the cage, it sounds like not enough tension on the chain which will show on the smallest sprocket

[nuttycyclist]

Is the deraileur properly mounted?   I had somebody the other day that had swivelled it backwards when changing a wheel.  Just needed turning back to where it should have been.

[LEE]

You could try a bit more tension on the cage which is the screw at the top of the cage, it sounds like not enough tension on the chain which will show on the smallest sprocket

Interesting. Never messed with that before.

[nuttycyclist]

You could try a bit more tension on the cage which is the screw at the top of the cage, it sounds like not enough tension on the chain which will show on the smallest sprocket

Interesting. Never messed with that before.

That's what I was trying to describe.  In my case it wasn't the adjustment screw, just that the whole unit had been swivelled backwards slightly and thus reducing chain tension.

[Zoidburg]

Are you missing the spacer?

Missing - the orientation of the cassette will be a mil out.

It could also be that if you rarely use the smallest sprocket the chain and the rest of the sprockets could be worn out of sinch with the smallest one so it always skips.

[Rhys W]

Yes, B-tension screw - it could be the upper jockey is too close and pushing the chain off?

Other than that, it's the kind of problem a bent derailleur hanger causes IME.

[Zoidburg]

Yes, B-tension screw - it could be the upper jockey is too close and pushing the chain off?

Other than that, it's the kind of problem a bent derailleur hanger causes IME.

It does but it would be out of whack over the whole cassette.

Unclamp the cable and re-index the mech using the smallest sprocket as the start point, you do that to ensure the cable is not too tight and holding the mech out of index at the start point - if it then refuses to run then something is borked.

[Kim]

It seems to be a fair rule of thumb that once gears start acting in mysterious ways the possibility of a bent hanger should be considered....

Why would the B-tension be an issue on only the smallest sprocket?  My understanding is that if it's right for the biggest, it's a non-issue on all the others.

[Biggsy]

My guess is that the cassette (or whole wheel in the dropouts) is fitted a tiny bit differently than it was before.  The fact the larger gears are working ok doesn't necessarily mean the indexing couldn't be improved.  Sometimes it's more critical to have just the right cable tension with the smaller sprockets.

B-tension mainly affects the largest sprocket position, but subtely affects all the others as well.  I doubt it's relevant anyway.

[Tewdric]

Not much to add, in that it could be a number of things.  Try to eliminate them one at a time.

In order of likelihood in the world according to Tewdric (which may turn out to be a random parallel universe!):

Bent,  knackered or worn tooth on the small cog
Stiff link in the chain
Derailleur cable a gnat's tadger too tense - ease off 1/4 turn clockwise looking rear-to-front and see if it helps
Wheel mounted incorrectly
Wheel bearings been serviced?  Spacers all in the right place?
Limit screw not set correctly
badly worn chain
Derailleur hanger bent (have alignment tool here if you fancy a ride in Monmouthshire!)
B screw badly adjusted or tab broken off mech
jockey wheels shagged

What's the cassette?  I might have a part-worn in the spares box with a good nick small sprocket you can try.

You are always welcome to come for an awayday and use the SICRUT BWNCWR if you want to.

[Oaky]

To add to Tewdric's list (at the bottom, probably less likely than the rest).

Is it possible the cassette's not quite seated correctly and is sitting further out? (caught on a wear ridge?)


EDIT: I just looked at the end of page 1 of comments, Biggsy already got this (and other related ideas besides)

[GruB]

As it has all been said I see no need to repeat the good advice.

But I am now curious as to the update Lee?  Have you fixed it? 

[LEE]

Fixed thanks to my LBS mechanic.

He noticed that the cassette lockring was actually touching the chain (usually there would be a very small gap).

I mean that the chain wasn't sitting fully on the smallest sprocket because it rested on the lockring first.  This allowed the chain to slip off the teeth of sprocket, especially under load.

This is 100% my fault.  When I swapped cassettes between wheels I obviously mixed up the 2 "identical" lockrings.  Fitting one with a slightly smaller diameter didn't have any effect on the other bike but fitting a larger one did.  The size difference isn't something you would notice, at least I didn't, I assumed thay they would all be the same size.

Motto:  Don't mix up your lockrings and, when all else fails, don't be afraid to ask your local LBS.

[toekneep]

Thanks for posting the solution Lee. Although I haven't felt qualified to contribute to the thread I learn a lot from these kind of exchanges and knowing the final solution is obviously required if the learning is to be effective. This is one of the best bits of YACF.

[GruB]

Yay  

[Zipperhead]

The size difference isn't something you would notice, at least I didn't, I assumed thay they would all be the same size.

Motto:  Don't mix up your lockrings and, when all else fails, don't be afraid to ask your local LBS.

I would have assumed that the lockrings are all the same size (from the same manufacturer) as well!

[Rhys W]

What was it, Campagnolo 12t lockring on an 11-up cassette?

[LEE]

What was it, Campagnolo 12t lockring on an 11-up cassette?

2 Shimano Lockrings.  2 Shimano Cassettes. An 8 speed cassette and a 10 speed cassette.

Note.  There are also spacer issues when doing what I did.

Depending on the hub used, a 10 speed cassette requires spacers between wheel and cassette whereas an 8/9 doesn't (because a 10 speed cassette is actually narrower, I don't know why they deisgned it this way, seems rather odd)

My Mavic hub and Shimano cassette requires 2 spacers, a 2mm and a 1mm.  I believe a Shimano hub just needs the 1mm (but it's worth remembering).