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Old 03-09-10, 03:28 PM   #1
chancho
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Erratic shifting on rear derailleur

Hi everyone,

I've been having trouble shifting my rear derailleur lately. I recently replaced the chain rings, cassette,
chain and rear derailleur. It was fine for a while but now I can't get it to shift correctly.

When I shift to a larger cog I either shift too far or not far enough. If I push the shift lever all the
way over (to the left), the chain will actually move over two gears. I've spent plenty of time adjusting the RD
with no effect--I'm starting to think that the problem must be with the shifters themselves. It seems
like I just can't add the right amount of tension to the cable when shifting--I add either too much or
too little. What ends up happening is that I end up somewhere between two gears and the chain
skips back and forth between them.

Does this sound like something anyone has encountered? The shifter is a Shimano 105 and I've been
using it for years, never had this problem before. I'm not extremely experienced adjusting the RD but
I find it hard to believe that I absolutely can't get the chain to cleanly get to all the gears while on the
stand.

Any help is appreciated.
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Old 03-09-10, 03:37 PM   #2
Panthers007
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Here are two links that should help:

http://www.parktool.com/repair/readhowto.asp?id=64

And:

http://bicycletutor.com/adjust-rear-derailleur/

I'd clean the derailleur and oil all the pivots, and install a new cable and housing.
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Old 03-09-10, 03:39 PM   #3
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Chanchito el problema es q estas usando shimano

Just kidding... hope nothing is messed up in the shifter itself because u cant repair the shimano brifters. Just in case, witch RD did you put and how did u set the brifters cables and RD? there is a procedure for that...
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Old 03-09-10, 03:42 PM   #4
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If you push the right brake lever all the way to the left it should shift 3 gears.
If the rear shift cable is not routed correctly at the derailleur fixing screw this could account for your problem. You may have the cable on the wrong side of the screw.
The parktool instructions, above, are good.
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Old 03-09-10, 09:02 PM   #5
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Sounds like too much friction for your derailleur's return spring, possibly.

To verify, shift through the gears while pulling the derailleur to keep the cable tight. If it shifts well like that, you need to reduce cable friction. If you've done everything you can to reduce friction (cleaning and lubing cables, cutting housings to the right length to minimise bends), you can try increasing the derailleur's return spring tension somehow... but since it's a new derailleur this shouldn't be necessary.

Or maybe that last is exactly wrong; I often see marketing guff about 'reduced shifting effort'... this could be at the cost of reliability.
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Old 03-09-10, 09:23 PM   #6
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I agree with the other posters. The first thing to do is to make sure that everything is in as-new condition. That means checking to be sure that everything is clean and smooth running. Another part of that is checking the derailleur hanger alignment. My bet is that'll fix it.
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Old 03-09-10, 09:56 PM   #7
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This sounds vaguely like what was happening when my old Deore XT derailleur was getting old. The pivots had so much slop that it wouldn't shift cleanly, and eventually pushed the chain off the big cog into the spokes.

I'd take everything off (including the chain) and wiggle the cage side-to-side. If you can feel play, it's probably toast.
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Old 03-09-10, 09:57 PM   #8
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New derailleur.
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Old 03-11-10, 07:40 AM   #9
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I have found that erratic shifting is sometimes caused by hubs improperly tightened after re-greasing. If the hub isn't tight enough with even slight axial play, it will really screw up the shifting. To check, simply grab the wheel at the top while it's in the drops and try moving it sideways. if you see it moving relative to the brake pads (a good reference point), it'e likely that the hub is slightly loose. Take the wheel out and tighten the cones slightly.
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Old 03-11-10, 07:46 AM   #10
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I have found that erratic shifting is sometimes caused by hubs improperly tightened after re-greasing. If the hub isn't tight enough with even slight axial play, it will really screw up the shifting. To check, simply grab the wheel at the top while it's in the drops and try moving it sideways. if you see it moving relative to the brake pads (a good reference point), it'e likely that the hub is slightly loose. Take the wheel out and tighten the cones slightly.
You can flex rims relative to the brakepad independent of whether the hub is adjusted loose or tight. You're looking for a loose/knocking feeling at different points of wheel rotation, regardless of rim flex.
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Old 03-11-10, 07:52 AM   #11
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Yeah, I was gonna say you feel play rather than see it.

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at different points of wheel rotation
Have you come across wheels that have play at only some points in their rotation? What would that mean, a bent spindle?

Last edited by Kimmo; 03-11-10 at 07:55 AM.
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Old 03-11-10, 08:20 AM   #12
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Have you come across wheels that have play at only some points in their rotation? What would that mean, a bent spindle?
Often, not quite sure of the technical explanation.

Probably just poor quality hub cone races/axles/bearings. Or parts in differing stages of wear. If there is a significant difference between spots (e.g binding/ultra loose) after adjustment is made you could suspect a bent axle. As a further confirmation, both park and barnetts tell you to test for play while rotating the wheel into different spots and re-testing.

Don't see much bent axles anymore since everything is 8/9/10 shimano/campy or 'proprietary' hub systems (e.g easton velomax, hed hubs, reynolds, dt swiss)
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Old 03-11-10, 09:04 AM   #13
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RD is new, as is the cable. Housing is old I believe. I'll try lubing the cable again...not sure why I didn't think of that before. I guess the next step after that would be to replace the housing. Some people tell me to replace the housing periodically. At my LBS they told me not to replace the housing unless I suspected it was causing a lot of friction.
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Old 03-11-10, 09:12 AM   #14
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Originally Posted by chancho View Post
RD is new, as is the cable. Housing is old I believe. I'll try lubing the cable again...not sure why I didn't think of that before. I guess the next step after that would be to replace the housing. Some people tell me to replace the housing periodically. At my LBS they told me not to replace the housing unless I suspected it was causing a lot of friction.
Replacing a cable without replacing, at the very least the rear derailleur housing loop is a waste of time. Additionally a very good majority of mechanics cut the rear loop too short - it should enter the derailleur nearly flat, not at an excessive angle. For example the included section of housing on a shimano kit is usually too short.

Sram road derailleurs exacerbate this by having a housing entry angle that requires a much longer section of housing than a standard shimano derailleur for example.

Additionally, you may also want to check the hanger for alignment. This will cause all sorts of indexing problems that cannot be adjusted out. Extremely common on road bikes with replaceable derailleur hangers.
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Old 03-11-10, 09:33 AM   #15
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Quote:
Originally Posted by operator View Post
Replacing a cable without replacing, at the very least the rear derailleur housing loop is a waste of time. Additionally a very good majority of mechanics cut the rear loop too short - it should enter the derailleur nearly flat, not at an excessive angle. For example the included section of housing on a shimano kit is usually too short.

Sram road derailleurs exacerbate this by having a housing entry angle that requires a much longer section of housing than a standard shimano derailleur for example.

Additionally, you may also want to check the hanger for alignment. This will cause all sorts of indexing problems that cannot be adjusted out. Extremely common on road bikes with replaceable derailleur hangers.


I seem to be seeing a lot of these lately. The last one was said to have been new but was well out of plumb.
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