fine tuning rear derailleur - across the whole cassette

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fine tuning rear derailleur - across the whole cassette

Postby nickj_d » Mon Nov 26, 2012 2:07 pm

Am looking for some tips on getting my rear cassette fine tuned so that it changes smoothly across the whole cassette (9 speed). I've set the upper and lower limits properly, and i've played around with the barrel adjuster, but no matter what I do, i can not get it to the point where it changes up and down smoothly across all gears! I can get perfectly good gear changes across 8 of the gears, but there's always one that doesn't shift smoothly (it's normally the second or third lowest).

Any tips?
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by BNA » Mon Nov 26, 2012 2:23 pm

BNA
 

Re: fine tuning rear derailleur - across the whole cassette

Postby scirocco » Mon Nov 26, 2012 2:23 pm

With those symptoms it's most likely the derailleur hanger is not straight. Probably took a knock at some point. The derailleur cage should be perfectly parallel with the plane of the cogs, and not twisted left or right when looking from the top. Best to check with a proper tool or guide, though.
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Re: fine tuning rear derailleur - across the whole cassette

Postby nickj_d » Mon Nov 26, 2012 3:18 pm

to my highly untrained eye, it looks ok, but that doesn't mean it is.

The thing is, i have the same problem on both my bike and my girlfriends. I have tried to tune both, but can't get either of them 100% right. The whole process seems a bit of trial and error for me.
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Re: fine tuning rear derailleur - across the whole cassette

Postby TCAT » Mon Nov 26, 2012 3:33 pm

Check the cables. I have had similar problems and eventually found the cable was slightly frayed.
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Re: fine tuning rear derailleur - across the whole cassette

Postby twizzle » Mon Nov 26, 2012 4:15 pm

TCAT wrote:Check the cables. I have had similar problems and eventually found the cable was slightly frayed.


+1. Or the outer is really old.

I ended up using avid rollamajigs on all my bikes (gets rid of the loop in the rear cable), but I've had a number of problems with bad shifts due to the cable guide on the bottom bracket not being as slippery as it should.
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Re: fine tuning rear derailleur - across the whole cassette

Postby master6 » Mon Nov 26, 2012 4:44 pm

:D
nickj_d wrote:The thing is, i have the same problem on both my bike and my girlfriends.


Really?
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Re: fine tuning rear derailleur - across the whole cassette

Postby rustychisel » Mon Nov 26, 2012 7:22 pm

9 speed you say?

4th cog.

If you're happy with the derailleur limit screws (high & low) then make sure your cable tension is right. Click down to smallest cog, cable relaxed, and it should be taut but not under tension. If you're happy with your cable, change to the fourth cog up (ie 4th smallest cog at rear) and use the barrel adjuster at rear of derailleur to fine tune. Get your 4th cog perfect and you're set. If not there's another problem needs identifying and addressing.
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Re: fine tuning rear derailleur - across the whole cassette

Postby winstonw » Mon Nov 26, 2012 7:24 pm

Other causes.
- If the chain or cassette are worn somewhat, you can struggle to keep the changes even across the cassette.
- poor cable installation (too long or short), sharp bends esp re entry inside frame, non optimal routing from STI levers along bars. smaller frames can have sharper bends in cables between bars, and down and top tubes.
- dodgy fine barrel adjustor action. some LBS marry Sram and Shimano bits, which isn't always a good thing.
- poor chain condition - not lubed well, or just plain dirty.
- chain the wrong length.
- RD jockey wheels worn.
- B screw poorly adjusted. read up on how to get guide wheel optimally close to cassette.

I generally tune for a good shift between 4th and 5th gear. This is then more likely to avoid larger errors at either end of the cassette.
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Re: fine tuning rear derailleur - across the whole cassette

Postby Alien27 » Mon Nov 26, 2012 9:24 pm

rustychisel wrote:...If you're happy with your cable, change to the fourth cog up (i.e. 4th smallest cog at rear) and use the barrel adjuster at rear of derailleur to fine tune. Get your 4th cog perfect and you're set...


Can you give a little more detail on this step? What do you mean by adjust at the rear derailleur to fine tune, do you tighten the cable till it pops up a cog, then go the other way till it pops back down, then set somewhere half way between? Thanks :)
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Re: fine tuning rear derailleur - across the whole cassette

Postby rustychisel » Tue Nov 27, 2012 12:17 pm

Hi Tom, just saw this...

Winston has given a pretty comprehensive list of things wot might not be good, but if things seem in the right place... for the rear derailleur with hi and low screws set appropriately, it all comes down to cable tension. In the detente position (ie least tension, cable slackened, corresponds to smallest cog) examine your cable tension. First make sure the shifter (STI) is actually at 'last click' and the cable head is properly installed etc. Then wind in the barrel adjuster completely (cable passes through it at rear of derailleur) and any inline adjusters. Take up any slack in the cable by undoing the cable anchor bolt (underside of derailleur) and tension cable, making sure you know exactly how the cable passes by the anchor bolt. Very lightly take up the tension using the barrel adjuster, the cable should be finger taut but not guitar string tight.

try shifting from smallest to next cog a few times to test if tension is correct at this point. shift up and down a few times over those 2 cogs. When you're happy, shift to 4th cog. Get down close behind the bike, directly in line, and have a close look at the chain path. Is it directly in line with the cog or slightly off centre. (You can sometimes get a hint of how close you are by spinning the cranks slowly backward and examining whether the chain and cogs are running smoothly or whether there's any 'binding' between the two, usually indicated by the chain slopping a little loose. Listen to the noise it makes, also).

Use the barrel adjuster to centre the guide pulley and therefore chain perfectly in line with the 4th cog. Wind the adjuster 1/4 turn or 1/2 turn at a time so you can easily go back if you adjust too far. Get down close behind the bike - directly in line - and eyeball the incremental movement of the derailleur cage. When you're happy with this, try changing gears up and down, one at a time, until you get to your lowest cog (best done using the small chainring at front to avoid cross-chaining and increased shifting difficulties).

The lowest gear (biggest cog) is usually the hardest to change into; it's bigger, the derailleur has to do more work, and the chain angle is the most extreme. I often find it takes a couple of revolutions of the cranks to change when a bike is on the workstand, but usually this isn't much of an issue on the road. I'd much prefer that, anyway, than have the chain overshift into the spokes, so I keep the low screw tolerance pretty tight.
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Re: fine tuning rear derailleur - across the whole cassette

Postby Alien27 » Tue Nov 27, 2012 9:38 pm

Thanks Rusty, much appreciated.
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