Centaur 11 rear mech wobbly????

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wheel71
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Centaur 11 rear mech wobbly????

Postby wheel71 » 2 Oct 2019, 5:42pm

Hopefully someone can help me. My centaur 11 rear mech seems overly wobbly at the mounting bolt area (mounting bolt is/was tight). I took it off and there's a circlip that just spins round but there dosn't seem to be any way to tighten it at all. Maybe I'm missing something or maybee it's always been like that and I never noticed but I don't think thats the case as the shifting is not as crisp as it has been. Any help much appreciated. Thanks.

Brucey
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Re: Centaur 11 rear mech wobbly????

Postby Brucey » 2 Oct 2019, 6:00pm

Image

the clip ( I think this one might be called an 'E-clip' in fact) is just there to hold the parts together when the mech is off the bike. When the top knuckle bolt is tightened nearly everything is pulled tight against the gear hanger. This includes the bolt, the E-clip, the B-tension adjuster. This leaves the body of the derailleur free to pivot round the static parts of the assembly.

On these mechs the top knuckle is sprung and the upper knuckle pivot has bushings that do wear. It is not at all uncommon for RDs of this type to wear out in the upper knuckle bushings.


However sloppy shifting has many possible causes, including

- bad cables
- worn pulleys
- worn pivots/bushings in the derailleur
- badly aligned RD
- worn chain
- worn (or loose) cassette

and on a well-used bike it is rarely a single thing that is the sole cause of iffy shifting. So I'd suggest that if you are not 100% sure, you should change the known-bad or at least cheap things first.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

wheel71
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Re: Centaur 11 rear mech wobbly????

Postby wheel71 » 2 Oct 2019, 6:13pm

Thanks for the reply. It is definately play around the mounting bolt. Gears still shift ok, just not quite as crisp. Maybe the bushing has worn out but the mech is a year old and has only done 6000km so I'd be surprised if it's worn out in that time. It is on my "all weather" bike but is cleaned and maintained regularly. I've been working on my own bikes for 45 years so am experienced but couldn't work this out.
Cables were also replaced a week ago so there's no problem there.

Brucey
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Re: Centaur 11 rear mech wobbly????

Postby Brucey » 2 Oct 2019, 10:56pm

I've not had that particular model apart but some mechs of that design have a steel sleeve that is pressed/formed into position within the top knuckle. If the RD takes a clout the sleeve can come loose. Occasionally it'll come loose anyway, and once it does its not easy to fix (I never managed it).

FWIW I've seen plenty of RDs wear out there (with just simple wear), normally on bikes that had rock-hard tyres and were ridden many miles on rough roads though; such wear in your mileage would indeed be unusual.

cheers
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Mick F
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Re: Centaur 11 rear mech wobbly????

Postby Mick F » 3 Oct 2019, 7:28am

How long have you had it?

My Chorus rear mech is perfect in every way EXCEPT the top pivot is worn causing it to be wobbly like wot you describe. It shifts ok-ish but not crisp and it's generally annoying because of that.

I've retired mine and bought a Campag Comp. When that goes the same way, I'll be forgetting Campag and fitting a Shimano Shadow that doesn't have a top pivot. Got one on my other bike, and it's brilliant.
Mick F. Cornwall

philvantwo
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Re: Centaur 11 rear mech wobbly????

Postby philvantwo » 3 Oct 2019, 7:45am

He's had it a year Mick F.
[color=#FF0000][/color]

Brucey
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Re: Centaur 11 rear mech wobbly????

Postby Brucey » 3 Oct 2019, 8:33am

this might sound like a daft question but how worn is the chain? Chains obviously elongate as they wear but they also get laterally worn, i.e. they become more flexible in a side-to-side sense. This does affect how easily the RD can push the chain from one sprocket to another.

Chains vary from one make to another, too, and so do sprockets; not every combination of parts will work equally well.

In a similar vein all the sources of free play in the RD add up; so this means that free play in

- the top knuckle
- the parallelogram pivots
- the bottom knuckle
- the upper (guide) pulley (teeth and/or bearing)

all contribute to the net vagueness in the shift. Pulleys can (very) easily wear out in 6000km, if the bearings are not well lubricated and/or the mech is slightly misaligned.

Years ago index systems usually had RDs with upper pulleys which deliberately had 'float' (free play) in them, and this gave the system a degree of tolerance to wear/maladjustment, i.e. the system could be misaligned by about 0.5mm and it would still run/shift cleanly. More importantly perhaps the upper pulley wouldn't see any side load in normal running. Often a little more life could be eked out of a worn RD by replacing the top pulley with a floatless one.

However in modern 10s (and higher) systems pulley bearings seem no longer to have 'float'; one way of looking at this is that the system is inherently less tolerant of wear and free play so you are better off without any from the start. However if a 'floatless' RD is out of line slightly then the upper pulley can wear rapidly in normal running, Both the teeth on the pulley and the pulley bearing can wear.

So an acid test is to grab hold of the RD at the top pulley and try and wiggle it from side to side. As a rule of thumb if it moves more than ~2mm side to side, it is probably going to affect the shift quality to some extent. However any degradation in shifting will also depend on everything else too eg b tension, hanger alignment etc etc. So its a judgement call as to what is worth changing; pulleys, chain, cassette, cables, RD alignment, RD setup, whole RD....

FWIW there is no 'right way' to repair a system of this type; some folk keep on top of their adjustments and can be expected to fettle the bike every few hundred miles as required. Others, meh, not so much. Thus (say) in an LBS near me a cash-rich, time-poor customer is liable to get a new chain, new cassette/chainrings, new cables and new RD if they turn up with a worn and misbehaving transmission. The logic is that this 'full reset' will give the longest service interval before the customer has to bring the bike back, and secondly the bike shop can warrant the work. This approach might make sense in that situation but I'd be unlikely to change all those parts at the same time on my own bike.

cheers
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Mick F
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Re: Centaur 11 rear mech wobbly????

Postby Mick F » 3 Oct 2019, 8:39am

philvantwo wrote:He's had it a year Mick F.
Sorry, I didn't read his second post.

Not long enough for top pivot wear, but how often has it been dismantled for greasing?
If it's dry, it could well have worn enough to be wobbly.

Mine got steadily worse over the years, and it wasn't until I'd checked out the play that I even knew it was a design problem.
Mick F. Cornwall

wheel71
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Re: Centaur 11 rear mech wobbly????

Postby wheel71 » 3 Oct 2019, 12:46pm

Loads of info there. I havn't time to read it properly now and will come back later. Thankyou all.
And I do ride on some very rough roads (someone mentioned that).

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Mick F
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Re: Centaur 11 rear mech wobbly????

Postby Mick F » 3 Oct 2019, 2:32pm

From what I remember ............ there's a thread on here about it, but goodness knows what the thread was called! .................. the bottom of the jockey cage would move in and out a centimetre. By close inspection, I could see the top pivot moving, not the parallelogram. The steel bolt had worn as well as the steel sleeve inside the top boss. After removing the mech and stripping it down, it was obvious what the problem was.

Brucey suggested that some PTFE tape wrapped round the bolt would cure it. Never tried. I just bought a new mech.

On the Moulton, the bike came with a Shimano Tiagra rear mech. That one ended up with the same problem - but much worse - and it only lasted 4,300miles from brand new.

I dumped it and fitted an XT Deore. The XT doesn't have a top pivot bolt, and bolts solidly onto the frame. FAR better design. :D
Mick F. Cornwall

wheel71
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Re: Centaur 11 rear mech wobbly????

Postby wheel71 » 3 Oct 2019, 3:55pm

Thanks everybody.

It's definitely the top knuckle that has the play in it. I'll just have to order a new one I suppose and hope it lasts longer this time.
I'll have a go at taking it apart when the new one arrives but as it's still usable at the moment I'm not doing that yet.

FYI.
Pulley wheels are still like new and there is no play where the cage is attached, just the top bolt knuckle. It's on a brand new frame now and was on a brand new frame before (first was temporary while I saved for the other). Brand new cable a week ago (inner and outer). Never been bashed. Chain is good and correct length. Cassette is same age as mech and fine. Bike is out in all weathers on rough roads and does lots of steep hills (I like a bit of Everesting) but well maintained.
Maybe it's just a bad part inside or something as it seems very premature to be that bad. My old Chorus one has done far more but is on my nice weather bike so gets a pretty easy life.

I have an audax in 9 days so better get it ordered. Just hope the old one dosn't disintegrate or anything silly in the meantime and leave me miles from home.

Thanks again. Tim.

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Re: Centaur 11 rear mech wobbly????

Postby Brucey » 3 Oct 2019, 4:11pm

FWIW I did suggest PTFE tape to Mick as a fix that would at least work temporarily; I've used it on cantilever brake bosses and it has lasted a lot longer than you might expect, but I've never tried it in a RD upper knuckle.
Disassembling the top pivot is easy; however reassembling it is often made difficult by the fact that the spring inside the pivot needs to be both wound up (preloaded) and compressed as you install it.

I have an idea that Mick's shimano mech didn't last long because it was strapped to a moulton; the suspension movement causes the RD to be 'on the move' all the time, even on relatively smooth roads. By contrast there are reports from touring riders (heavy bike, squashy tyres) of RDs (with similar upper knuckles) that lasted tens of thousands of miles; I can only assume that the mech isn't flapping about in the same way on these bikes.

cheers
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Mick F
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Re: Centaur 11 rear mech wobbly????

Postby Mick F » 3 Oct 2019, 8:28pm

"flapping about"

That's the issue.
Change the design to a Deore XT and all the flapping about will cease.
Mick F. Cornwall

Brucey
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Re: Centaur 11 rear mech wobbly????

Postby Brucey » 3 Oct 2019, 8:42pm

well, the flapping about will still occur to some extent, but there will be less of it, and the it will just be at the lower pivot instead, which is better able to withstand it. The main parallelogram pivots still see a lot of load of course. I think the net rates of wear are probably lower than with a mech that has two sprung pivots though.

FWIW I have an RD-M772 which has been well used (not by me) and then 'retired' and it was starting to get a bit sloppy in both areas. I was going to mention this mech in another thread, and may still do so.

cheers
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Mick F
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Re: Centaur 11 rear mech wobbly????

Postby Mick F » 3 Oct 2019, 9:22pm

My rear mechs on Mercian .......................
The Chorus rear mech lasted 21,000miles.
Changed for a Campag Comp in August 2014 and about 5,000 miles done since then. Still perfect of course.
Mileages are less on Mercian these days because of riding Moulton far more.
Mick F. Cornwall