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Old 01-17-10, 04:29 AM   #1
DArthurBrown
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Trek 4300 rear derailleur return sluggish

2007 Trek 4300, Alivio rear derailleur with about 2000-3000 miles on it.

The shifting has been gradually getting worse over the past year. The hanger is straight. I've cleaned and lubed the cable, and have removed as much grit from the derailleur itself as I can.

Here's the issue. Start in the small cog and shift through the gears to large cog to check indexing. Indexing is good. Now from the large cog, release the cable through the gears toward the small cog. The derailleur won't release enough to get to the next smaller cog reliably. If I gently pull on the derailleur body, I can nudge it toward the smaller cog and it will stay well enough to shift, but it will stick again on the next shift.

If I use the barrel adjuster to align the indexing properly for releasing cable tension, downshifting won't make it to the next larger cog. I'm wondering if it's possible the spring has worn out. It doesn't seem like I should be able to pull the derailleur outward and have it stick. By contrast, my 105 RD on my road bike releases all the way, and when I tug outward on it (gently) there is no movement.

Any ideas?
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Old 01-17-10, 05:22 AM   #2
onbike 1939
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This is usually caused by corrosion within the small loop of cable leading to the RD. Replace the outer cable and lube a pivots on the RD.
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Old 01-17-10, 01:16 PM   #3
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Originally Posted by onbike 1939 View Post
This is usually caused by corrosion within the small loop of cable leading to the RD. Replace the outer cable and lube a pivots on the RD.
+1. Cables are cheap and they're most frequently the cause of issues like this.
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Old 01-17-10, 01:22 PM   #4
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Originally Posted by DArthurBrown View Post
2007 Trek 4300, Alivio rear derailleur with about 2000-3000 miles on it.

The shifting has been gradually getting worse over the past year. The hanger is straight. I've cleaned and lubed the cable, and have removed as much grit from the derailleur itself as I can.

Here's the issue. Start in the small cog and shift through the gears to large cog to check indexing. Indexing is good. Now from the large cog, release the cable through the gears toward the small cog. The derailleur won't release enough to get to the next smaller cog reliably. If I gently pull on the derailleur body, I can nudge it toward the smaller cog and it will stay well enough to shift, but it will stick again on the next shift.

If I use the barrel adjuster to align the indexing properly for releasing cable tension, downshifting won't make it to the next larger cog. I'm wondering if it's possible the spring has worn out. It doesn't seem like I should be able to pull the derailleur outward and have it stick. By contrast, my 105 RD on my road bike releases all the way, and when I tug outward on it (gently) there is no movement.

Any ideas?
You need to take the cable + housing out of the equation to have applicable results in the test you tried to perform. Manually push the derailleur through the range once the cable is disconnected to inspect how well it travels. You'll have your answer about the cable/housing there.

Other things you may keep in mind that affects shifting performance

1) Derailleur hanger alignment
2) Excessively worn chain
3) Excessively worn pulleys
4) Short rear derailleur housing loop. 99.9% of the r.d sections that come with "new" bikes are too short as well as the ones in say shimano cable kits. This inhibits shifting to the small cog. You'll note that as the derailleur takes up slack in the larger cogs, the housing stop on the derailleur will require a greater length of housing.

None of this is relevant if you're not using the correct procedure to adjust the rear in the first place:

http://www.parktool.com/repair/readhowto.asp?id=64
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Old 01-17-10, 08:55 PM   #5
DArthurBrown
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I replaced the derailleur cable and the housing and that fixed the problem. Thanks for the suggestions.
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