Worn rear derailleur?

[Mick F]

I think - but I don't know - that my Campag Chorus rear mech is coming towards end of life.
It's a medium cage, 10sp, done about 21,000miles, and I recently fitted new jockey wheels.

Symptoms are difficult to describe because wear always happens so slowly and gradually.

I feel - though I can't be certain - that gear changes aren't as sweet and crisp as they should be. Sometimes I get a "half way house" effect in a mid-cassette gear and have to click to another cog. Sometimes too, when I shift to the big cog or its next-door-neighbour, the cog selection "hunts" up and down between them. These things are rare events, but I'm sure they never used to happen in the past.

No, it's not the rear mech adjustment or the RH Ergo causing this and the RH G Springs replaced 5,000miles ago.
Fairly new chain and fairly new cassette BTW.

This morning, I grabbed the bottom of the jockey cage and moved it in and out to see the bottom moving maybe 10mm. By looking closely and feeling the parallelogram joints, I could see that all the backlash was coming from the top pivot where the mech is screwed to the dropout. The bolt is tight. The play is in the boss. Parallelogram feels fine.

I cannot say if it's always been like this as I've never done this test before.

Also, I've never in my whole life used a rear mech for 21,000miles, so I'm really out of my depth here.

Any advice please?

[NATURAL ANKLING]

Hi,
In my recent and limited experience, chain suck and vague gear changes have been worn derraliers back or front.

[531colin]

Blow a pound on a new gear wire before you blow however much it is for a new mech....

[fatboy]

Blow a pound on a new gear wire before you blow however much it is for a new mech....

+1 and chnage the last bit of outer too. I convinced myself I needed a new rear mech but what I should have changed was the short bit of outer. Now I know that my maintenance is way below yours and you probably know how to suck an egg too.....just I felt a right twerp ( or worse!) when I worked out the real cause of my problem!

[Valbrona]

Blow a pound on a new gear wire before you blow however much it is for a new mech....

Blow a few hundred quid on some 2015 11 speed Athena triple kit instead.

[Mick F]

yeah ok.

Seriously though folks, how do you tell that your rear mech is worn?

[Edwards]

I do what you did Mick but before or as well as a new mech I change the inner and outer cables.

[NATURAL ANKLING]

Hi,
For me the jockey cage leans into the wheel and if you grab it it can be straightened by taking up the slop

[CREPELLO]

I reckon you'd get ghost gear changes whilst hauling the bike around a (bumpy) corner at speed.

[jb]

Well, in worn dérailleurs the top jockey is no longer perfectly parallel with the sprocket, and because its centred slightly above the pivot point of the cage as the cage rotates it can move the chain from side to side. The only way of telling whether the wear is too bad is if it works ok in a chain ring you don't use much like the inner one but its not conclusive.
The best way is take note of the slop when new to give you an idea of how worn it is, bit late now though.

[sreten]

Hi,

I imagine a worn rear deraileur will allow you to twist the parallelogram
and just generally have very sloppy moving parts all over the place, i.e.
it doesn't do its basic job very well any more (moving a fixed arc) and
will get out of shape more with things like cross chaining torque.

Its a 30 sec job off the bike to ascertain the "slop" of the moving parts.

(FWIW for hifi tonearms about 10 seconds, but they can be adjusted.)

I'm assuming new jockey wheels come with all parts, and are not an issue.

rgds, sreten.

[tatanab]

I have just checked 4 medium and long cage Campag rear mechs of various vintages.

1. Racing Triple 8 speed. Lightly used, a very small amount of movement in the upper pivot. Shifts flawlessly with Veloce Ergo levers.
2. Racing Triple 8 speed. Very heavily used (more than Mick F's). This has been on my hack since 1998 and out in all conditions. About 2002 the casting around the top pivot split but has not caused any problems. There is a lot of play in the top pivot and also in the lower pivot where the jockey cage connects. I can easily move the bottom of the jockey cage 10mm sideways. It still shifts adequately, but this is with indexed down tube levers so I probably compensate for the wear by overshifting a bit when moving to a larger sprocket - no need when going to smaller sprockets.
3. Racing T 9 speed, a late one with the B screw on the jockey cage. Bought used. In good condition. Some play in the top pivot. I can move the bottom of the jockey cage about 5mm sideways. Works adequately well with 8 speed Record Ergo levers and an 8 speed cassette.
4. Comp Triple 10 speed. I've only used this for about 6000 miles, so is pretty new. I can see a little movement in the upper pivot, and I can move the bottom of the jockey cage maybe 5mm sideways - remember that this is a long arm, all others are medium. It shifts flawlessly with Centaur Ultrashift levers.

None of the mechanisms show any movement in the joints of the parallelogram. All have good condition jockey wheels.

So, the worst shifting I have is probably the 9 speed Racing T, but I am using mismatched parts so can compensate a bit when changing gear. I have it set so that it changes well when moving to a smaller sprocket, but certain movements to bigger sprockets require me to over shift a little - sometimes going 2 clicks and then instantly returning by one. Coincidentally this is in the middle of the cassette which is Marchisio so another source of slight mismatch.

[ukdodger]

MIck - 21k miles!

Just buy a new one mate.

[Mick F]

Yes, I probably will do. Whatever happens, 21,000miles is far enough, and even further will make matters worse.

Thanks Tatanab, good information. Nice to hear how things are and should be. Mine is easily 10mm waggle.

Out on a long 80odd mile ride yesterday. I lost count of the times the gear selection hunted between the two big sprockets. Seemed to happen at "wheel rate" as the chain went up and down the ramps between the sprockets. In order to stop it, I had to hold the RH paddle lever over hard. During this hunting, the Ergo was in the correct position and it wasn't caused by it either. It was the whole rear mech moving in and out.

I'm going to take it off later this morning. The securing bolt is passed through the top pivot and there are two O seals. Basically, I cannot see how it could wear there, so maybe all the problem is caused by squashed old O seals allowing too much play.

For the cost of two new O seals, it may be worth an experiment. Back later to this, after I've had a tinker.

[Mick F]

In bits.
Not me, my Chorus rear mech.

This is the hanger bolt that secures the rear mech to the dropout.
The O seals seem perfectly fine, but you can see wear on the bolt near the outer head where the chrome plating is rubbed away. No doubt the internal boss is worn likewise.

I'll re-assemble and await a new Comp derailleur I've just ordered. I could only find one - GB Cycles - despite Googling for ages.