Adjusting rear derailleur...
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Adjusting rear derailleur...
Postby lump_a_charcoal » Tue Nov 06, 2012 6:17 pm
After having my bike serviced by a shop last week, I noticed that when back pedalling, the rear derailleur starts to derail the chain - not handy when trying to trackstand, something I am practising. I didn't do it before the service.
What is this a symptom of?
It is Ultegra, by the way.
Thanks.
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Re: Adjusting rear derailleur...
Postby Reman » Tue Nov 06, 2012 8:07 pm
The problem is probably the index alignment is slightly out. change gears to the middle and see if the cog and closest jockey wheel line up using a screw driver.
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Re: Adjusting rear derailleur...
Postby Stuey » Tue Nov 06, 2012 10:15 pm
You could firstly try lining the top jockey wheel with the large rear sprocket by eye from behind the bike, while tweaking the adjuster.
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Re: Adjusting rear derailleur...
Postby twizzle » Tue Nov 06, 2012 10:53 pm
Pedalling backwards. Don't do it. Seriously, it's not designed to work that way.lump_a_charcoal wrote:What is this a symptom of?
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...real cyclists don't have squeaky chains...
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Re: Adjusting rear derailleur...
Postby Stuey » Tue Nov 06, 2012 11:54 pm
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Re: Adjusting rear derailleur...
Postby DJIntegr8 » Wed Nov 07, 2012 7:47 am
Brendan
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Re: Adjusting rear derailleur...
Postby rkelsen » Wed Nov 07, 2012 9:45 am
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Re: Adjusting rear derailleur...
Postby twizzle » Wed Nov 07, 2012 9:51 am
Hey lump_a_charcoal - don't forget to insist that people who suggest fiddling with the derailleur offer to come and fix it personally if you bugger it up. If the limit screws aren't set properly, dropping the chain into the spokes or the frame is always a good look.
...real cyclists don't have squeaky chains...
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Re: Adjusting rear derailleur...
Postby lump_a_charcoal » Wed Nov 07, 2012 10:21 am
Let me clear one thing up - when I say back pedalling, I don't sit there clicking away like an idiot, I am talking about a brief 1/4 to 1/3 reverse rotation, if that much.
When taking off, I tend to do it with the pedal in the same spot. I get it there by back pedalling, because the bike tends to move if I do it the other way.
rkelsen, I find it helps. maybe a 1/10th forwards against the brakes, then back a bit. Hard to explain, but it helps me.
DJI, no, it is the same chain.
Thanks again.
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Re: Adjusting rear derailleur...
Postby twizzle » Wed Nov 07, 2012 11:55 am
...real cyclists don't have squeaky chains...
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Re: Adjusting rear derailleur...
Postby Stuey » Wed Nov 07, 2012 5:19 pm
The chain bunches up against the top jockey wheel and causes the problem, because there's limited tension on the bottom chain run - it's not usually that the chain is guided off the top/side of rear (cassette) sprocket from the front. If the jockey wheel is in the right spot laterally, it runs smoothly. I didn't suggest adjusting the limit screws at all - I referred to fine tuning with the cable adjuster.twizzle wrote:How does adjusting a derailleur which is *behind* the cassette affect anything when you back pedal.
Hey lump_a_charcoal - don't forget to insist that people who suggest fiddling with the derailleur offer to come and fix it personally if you bugger it up. If the limit screws aren't set properly, dropping the chain into the spokes or the frame is always a good look.
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Re: Adjusting rear derailleur...
Postby twizzle » Wed Nov 07, 2012 10:04 pm
Re. "not usually"... keep dreaming. The chain has to derail from the leading side, not the trailing. Otherwise the teeth engaged in the links keep it on.Stuey wrote:The chain bunches up against the top jockey wheel and causes the problem, because there's limited tension on the bottom chain run - it's not usually that the chain is guided off the top/side of rear (cassette) sprocket from the front. If the jockey wheel is in the right spot laterally, it runs smoothly. I didn't suggest adjusting the limit screws at all - I referred to fine tuning with the cable adjuster.twizzle wrote:How does adjusting a derailleur which is *behind* the cassette affect anything when you back pedal.
Hey lump_a_charcoal - don't forget to insist that people who suggest fiddling with the derailleur offer to come and fix it personally if you bugger it up. If the limit screws aren't set properly, dropping the chain into the spokes or the frame is always a good look.
And re. limit screws, some lazy people rely on the indexed shifting to keep the chain on and don't adjust the limits. Especially if they have different wheel sets with different offsets on the free hub that require the RD to be adjusted when swapping wheels. Unless you have checked them, you should assume they are not set properly.
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Re: Adjusting rear derailleur...
Postby Stuey » Thu Nov 08, 2012 12:14 am
The chain travelling backwards passes over the cassette, contacts the top jockey wheel slightly too far off centre so the chain binds and piles up on the top jockey wheel. This is partly because of the lack of full tension in the bottom run due to the der. spring - if it was under full tension, the chain would just be pulled through. Usually this is accompanied by the jockey wheels 'bouncing' and clacking. The top chain run can then lift off the sprocket of the cassette, like a train derailment type pile up, to use a recent Melburnian metaphor to explain how it works.
FYI, the reason I wrote 'usually' is because in cases of extreme cross-chaining when pedalling backwards, it could be that the top run of chain is guided off the chosen rear sprocket of the cassette, like in a typical chain drop situation. It's not because I was having a half-hearted punt at an explanation. But 'usually' it's what I said.
Take it or leave it, Twiz, me old mate!
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Re: Adjusting rear derailleur...
Postby twizzle » Thu Nov 08, 2012 6:17 am
However - I still say "don't do it"!
lump_a_charcoal - derail or jam? If it's jamming, check that the guide jockey wheel isn't running against the cassette, it could be the B screw has been adjusted to make it too close.
Sent from my iThingy...
Edit: Smiley added.
...real cyclists don't have squeaky chains...
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Re: Adjusting rear derailleur...
Postby lump_a_charcoal » Thu Nov 08, 2012 7:59 am
It starts to derail, towards the smaller cogs.twizzle wrote: lump_a_charcoal - derail or jam?
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Re: Adjusting rear derailleur...
Postby twizzle » Thu Nov 08, 2012 8:37 am
Big chain ring?lump_a_charcoal wrote:It starts to derail, towards the smaller cogs.twizzle wrote: lump_a_charcoal - derail or jam?
If not... maybe start looking at the freehub body, if it's not turning freely the chain will go slack which gives it a lot more room to drop.
And.... there's always Ui2. Upgraditis solves many problems.
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Re: Adjusting rear derailleur...
Postby ironhanglider » Thu Nov 08, 2012 11:39 am
First call would be to check the hanger alignment, the jockey wheels should be pointing in the same direction and parallel to the bike wheels.
If the derailler is pointing in the right direction (ie the hanger is not bent) then it could be that the jockey wheel is sitting too close to the inboard side.
If this is true then he'd also find changing gears on the stand would be really good when going to a lower gear (bigger cog) and less good when going to a higher gear (smaller cog). This is a characteristic of there being a little too much cable housing to the rear derailler (the tension on the cable doesn't change). Try winding the cable housing adjusting screw in a notch or two to shorten the cable housing and see if it improves.
The adjusting screws can not cause the problem as described (or at least as I understand it).
Cheers,
Cameron
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