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I just put a used SRAM XO derailleur, long cage, on my drive train. I cut the new chain to the proper length (big ring + big cog + 2), but the chain sags like a laundry line. The rear derailleur shifts great, and there is nothing wrong with the spring that regulates the movement along the cogs.

The problem seems to be that the spring(?) that controls the rotation of the cage about the top pulley seems to be weak. If the bike is just sitting there, I can tap the cage and it will just dangle.

Is this fixable, and more important, what impact does it have on riding?
 

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Never trust a fart
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Its possible the reason it was up for sale was the weak spring for the cage tension.

Just a thought.

No its not fixable, and it can allow the chain to slap around on the bottom of the chain stay and might cause a shifting issue.
 

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VanHalen said:
I just put a used SRAM XO derailleur, long cage, on my drive train. I cut the new chain to the proper length (big ring + big cog + 2), but the chain sags like a laundry line. The rear derailleur shifts great, and there is nothing wrong with the spring that regulates the movement along the cogs.

The problem seems to be that the spring(?) that controls the rotation of the cage about the top pulley seems to be weak. If the bike is just sitting there, I can tap the cage and it will just dangle.

Is this fixable, and more important, what impact does it have on riding?

Check that you have the B spring installed on the RD hanger properly, also tighten the B spring to increase chain tension...

Do you have the correct chain length, shift Big to Big then RD should be fully extended...chain tight even without a spring.

Check with LBS you can get new torque springs at least for shimano's.
 

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Never trust a fart
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The B screw adjustment will not solve his problem. There is too much play - spring is week.

http://sheldonbrown.com/derailer-adjustment.html#btension

Modern derailers have two spring-loaded pivots. The lower pivot, sometimes called the "a pivot" winds the cage up to take up slack as you go to smaller sprockets. The upper "b pivot" adds additional slack take-up ability by pushing the derailer's parallelogram backwards.

The tension of the two springs needs to be balanced for best shifting.

Most derailers have an angle adjustment screw (Shimano calls it "B-tension adjustment"). This adjusts the tension of the upper ("b") spring of the parallelogram, and thus the height of the jockey pulley. The looser this screw is, the closer the jockey pulley will be to the cluster.

The angle adjustment will need to be set according to the size of the largest rear sprocket. If you change to a cluster with a larger or smaller low-gear sprocket, you will need to re-adjust this setting. You will also need to adjust this if you change the length of your chain.

If the angle adjuster is set too loose, however, the jockey pulley will bump into the largest sprocket when the bicycle is in the lowest gear (large rear, small front). This is the gear you should check the adjustment in.

Since a derailer shift is caused by forcing the chain to run at an angle, the greater the angle, the sooner it will shift. The closer the jockey pulley is to the cluster, the sharper the angle will be for a given amount of sideways motion of the derailer. Thus, the looser the angle adjuster screw is, the better the shifting will be.
 

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I have an X9 rear that after having the wheels off for transport I had almost zero tension on the chain. Somehow, the cage (or whatever) had slipped past the small metal tab that sets up the tension. Hard to describe but once I wrestled the cage back behind the tab and re-mounted the wheel all was good. This was a nearly brand new rear der.
 

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And I don't mean the band
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Discussion Starter #6
Here's a pic. I took it out for a test ride, and the shifting is actually phenomenal, very fast, smooth, and precise. The only 'problem' I was having was the extreme chain slap noises. I guess it runs fine for now, will be racing it on Saturday, but when the economy comes back I'll buy a nice new one :D

<a onblur="try {parent.deselectBloggerImageGracefully();} catch(e) {}" href="https://1.bp.blogspot.com/_F5HwKzzD8jU/Ssy2wD8yhHI/AAAAAAAACp0/wpsKoNoZQo8/s1600-h/kdk_0031.jpg"><img style="margin: 0pt 0pt 10px 10px; float: middle; cursor: pointer; width: 288px; height: 218px;" src="https://1.bp.blogspot.com/_F5HwKzzD8jU/Ssy2wD8yhHI/AAAAAAAACp0/wpsKoNoZQo8/s320/kdk_0031.jpg" alt="" id="BLOGGER_PHOTO_ID_5389883790865892466" border="0" /></a>
 

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i dont see too much chain droop if that was your thinking..now the chain slapping around is harder to pinpoint...maybe a softer material on the chain stay will help...is your chain worn out?
 

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And I don't mean the band
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Discussion Starter #9
Fixed it!

I even wrote up a little guide that might help other people to diagnose this and other problems (with a SRAM derailleur)...

http://aubryvg.blogspot.com/2009/10/rd-cage-spring-repair-guide.html

maybe idea for sticky?

Anyway to answer some of the people's questions, the chain is brand new (1 ride on it), the cassette is brand new, so is the front derailleur (X7). I use a RaceFace Evolve XC crankset, with brand new Shimano Hone chainrings (22-32-44).
 

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cool...i've never opened an sram...but i've seen those tension holes before in shimano RD's..but your trick is new to me, add the extra tension but in the 'looser' hole...nice and clever dude
 

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And I don't mean the band
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Discussion Starter #11
adamantane said:
cool...i've never opened an sram...but i've seen those tension holes before in shimano RD's..but your trick is new to me, add the extra tension but in the 'looser' hole...nice and clever dude
LOL im not a dude :winker:
 
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