Derailleur jockey wheel hitting cassette - where am I going wrong?

seven stars

I just replaced the cable on my rear derailleur/derailer, but the jockey wheel is hitting the smallest couple of sprockets. I've tried adjusting the B tension screw, but it doesn't seem to make any difference. Any ideas?

I've looked online, but nothing I've found has helped so far. Chain length and components shouldn't be an issue, because this was all previously working before. I'd appreciate any help on this.

Woody_FX

You will see a screw by itself at the back of the derailleur (not the 2 beside each other) and it you screw this in further it will extend out the derailleur more (lower) and it should not hit the cassette then.

Since cassettes come with different sized cogs you may need to adjust this if you go from a 23 tooth cog to a 28 tooth or the similar.

Should be some youtube videos on this. Its not difficult thing to adjust.

seven stars

Woody_FX wrote: »

You will see a screw by itself at the back of the derailleur (not the 2 beside each other) and it you screw this in further it will extend out the derailleur more (lower) and it should not hit the cassette then.

That's the one I've been tinkering with (seems to be called a 'B' screw from what I've read today), but it hasn't made any difference and it's already in as far as it'll go.

I haven't changed anything else, so it's a bit frustrating!

doozerie

Is the B screw actually bearing against anything? If it is not pushing against anything then this would explain why turning it has no effect. The only cause of that that springs to mind, other than damage, is that the derailleur is (very) loose where it is bolted to the frame/dropout.

Is the spring in the derailleur (around the bolt holding the derailleur to the frame) still working/connected? Test this by rotating the entire derailleur clockwise, moving the jockey wheels away from the cassette. If it doesn't spring back then the spring may be detached - shouldn't really be the cause of the problem you are experiencing though, I reckon, as the B screw should still physically impede the derailleur from swinging too far toward the cassette, but it might suggest significant issues with the derailleur generally.

bcmf

Release the cable form the securing bolt so the cable is free.
Is the jockey wheel still making contact?
I reckon the cable is snagged somewhere either coming outta the shifter or under the bb area.

seven stars

Thanks for the help with this lads.

doozerie wrote: »

Is the B screw actually bearing against anything? If it is not pushing against anything then this would explain why turning it has no effect. The only cause of that that springs to mind, other than damage, is that the derailleur is (very) loose where it is bolted to the frame/dropout.

Yes, the screw's bearing against the derailer dropout, and the derailer seems well bolted to it. When I say that turning it has no effect, I mean that it doesn't improve things either way (and it's already at maximum tightness).

Is the spring in the derailleur (around the bolt holding the derailleur to the frame) still working/connected? Test this by rotating the entire derailleur clockwise, moving the jockey wheels away from the cassette.

I tried what I think you suggested, and the spring seems fine.

seven stars

bcmf wrote: »

Release the cable form the securing bolt so the cable is free.
Is the jockey wheel still making contact?
I reckon the cable is snagged somewhere either coming outta the shifter or under the bb area.

I tried this, but the jockey wheel is still rattling off the smaller sprockets.

bcmf

When you pull down the jockey wheel and cage away from the sprockets does it spring back.
Did you remove the rear mech at all. I think you may have a prob with the return spring for your jockey wheel and its cage - If you are happy that the 'B' screw is connected.Remember the 'B' screw makes a very small adjustment

seven stars

Nope, didn't remove the rear mech. The jockey wheels are fairly well-sprung as far as I can tell - I don't think I can pull the top one down without pulling them both, but when I do that they both spring right back.

Some additional symptoms. When the cable is attached and bolted, here's what happens:

Big chainring: With the chain in the highest gear (small sprocket rear, big chainring), everything looks more or less ok. In fact, in the big chainring at the front, all the rear gears seem fine.

Middle chainring: In the middle chainring at the front, the derailer won't shift to the smallest sprocket at the rear at all. In the 2nd smallest and 3rd smallest sprocket, the jockey wheel is hitting off the cassette (obviously the chain itself is between them, but the jockey wheel is bumping away on it as the chain goes round). The other sprockets on the rear seem to work ok.

Small chainring: In the smallest chainring at the front, nothing works at the rear. The jockey wheel is battering away on the cassette, and the chain looks way too slack.

Quite the situation I've gone and got myself into!

victorcarrera

seven stars wrote: »

Big chainring: With the chain in the highest gear (small sprocket rear, big chainring), everything looks more or less ok. In fact, in the big chainring at the front, all the rear gears seem fine.

Might not be related to the cable replacement. I think the chain might be worn or too long. As a rule of thumb with chain on big chainring and smallest sprocket the rear mech cage should be vertical.

bcmf

With Victor onthis that your chain is either cacked or too long. How/why jts int happening now I don't honstly know. Maybe it was set up before to cope with too much slack.

doozerie

Forget what I said earlier about rotating the derailleur, I'd confused myself and ending up talking complete rubbish. Sorry. The derailleur is sprung so that it resists the anti-clockwise rotation of the upper jockey wheel towards the cassette. So if you try to rotate the main body of the derailleur so that the upper jockey wheel touches (or almost touches) the cassette then the derailleur should spring back clockwise.

For that reason I don't see that an overly long chain, with the extra slack that it introduces, could cause the upper jockey wheel to be pulled up against the cassette. This assumes that the B screw is adjusted correctly and if you changed nothing other than the gear cable (which shouldn't affect this adjustment at all) then the B screw should have been fine since you had no problems previously. If anything it's a chain that is (far) too short that would be more likely to give your current problem, but if that were really the issue here then you'd have serious problems using the big chainring at all.

A chain that is too long would cause another issue though - the lower jockey wheel would swing up so far (to take up the slack) that the section of chain running from lower jockey wheel to chainring would come into contact with the section of chain running around the upper jockey wheel. This would certainly cause you problems but not the one you seem to be describing.

So assuming that your B screw isn't somehow malfunctioning, which seems unlikely in the circumstances that you describe, I can't think of anything specifically derailleur-related that would explain your problem. One thought though - is your rear wheel seated correctly? If the derailleur hasn't changed position from before then maybe your cassette/wheel has - basically, if you have vertical dropouts then maybe the wheel isn't slotted all the way in. I find the most reliable means of seating and centre-ing the wheel is while the bike is on the ground - open the rear skewer and let the weight of the bike settle it down onto the wheel before locking the skewer again. It's a quick and easy thing to check and worth a try before looking at more obscure possibilities.

seven stars

Lads, thanks for all your efforts at diagnosing this.

doozerie wrote: »

since you had no problems previously.

I did give this impression, but that was mostly to simplify things. The truth is that I'd been having a few shifting problems, which I initially thought was to do with cable tension: I could easily shift small>large sprocket, but less so the other way round. Before I found the root cause (the gimped cable), I played with the barrel adjuster slightly and I lubricated the derailleur itself. I was cycling for a few weeks after this btw. Things maybe weren't working great, but they were at least working.

@doozerie: cheers for going through the possibilities there. The rear wheel is seated correctly, so I think I can rule that out. I think the B-screw works ok, but I'll take another look there.

@victorcarrera: I tried the big chainring / smallest sprocket combo, and the rear mech cage is more or less vertical.

@bcmf: The chain could probably do with replacing anyway, but I'd doubt whether it could be the sole cause of the problem. Certainly I'm not experiencing any of the chain-related symptoms doozerie mentioned.

Icyseanfitz

remember the b tension screw makes very minor adjustments, looks like nothing is happening even though it is, whats the chain slack like when you have it in small up front, small at the back?

seven stars

Icyseanfitz wrote: »

remember the b tension screw makes very minor adjustments, looks like nothing is happening even though it is, whats the chain slack like when you have it in small up front, small at the back?

Chain is very slack in that combination. I'll upload a few pictures of what's going on..

seven stars

Chain outrageously slack with small chainring at front, small sprocket at rear. Derailleur shape doesn't look too clever here!:




Derailer position in big chainring at front, smallest (or 2nd smallest) at back. More or less vertical:




B-tension screw, now at maximum tightness:




Gimped derailleur closeups (middle ring at front, 2nd smallest at back), jockey wheel hitting cassette:

bcmf

Sweet Mother of baby Jesus look at the lenght of that chain.
Take at least 700 links out of it.
Move the b screw so its half way in or out or whatever.
In the first pic the chain should just be clearing the jockey wheel cage. When you move up thru the gears the cage takes up any slack etc

Cayo

I'm no expert but I think you got your answer in post No. 8.

I had a similar issue last weekend after removing that spring to put a bit of grease in there. There was a small rusty streak starting to appear. Of course I put it back together wrong on my first attempt and ended with a similar result to your picture above.

Also, just went to my bike and removed chain off the front ring. Jockey wheel didn't touch the cassette so don't think it would have anything to do with chain length.

Just my 2c, but like I say I'm no expert.

doozerie

From those pictures I'd wonder whether the stop screw (assuming the Alivio uses a screw for this) on the jockey wheel cage is missing. See pic 4 here, its what stops the jockey cage from rotating further than it should.

It looks like the cage is rotated very far up (anti-clockwise) in the first picture, although I've not looked at a long cage rear mech in a while so I'm a bit blurry as to what's a "normal" position for one these days.

Otherwise I'd still wonder about the state of the spring around the bolt holding the derailleur to the frame (pic 2 of the link above).

victorcarrera

Removing 4 or 6 half links should do it.

Icyseanfitz

yup too much chain slack, remove some links and your problem should go poof

seven stars

I'm happy to try removing chain links if needs be, but it seems odd that there were no chain slack issues at all previously. I'm inclined to think something else is the cause of this, as cayo and doozerie suggested.

The spring/screw/bolt might well be gone in the jockey wheel, but nothing looks obviously out of place to me. I can't see any empty screw/bolt housing, and there still seems to be fair bit of spring in the jockey wheel/derailer.