Deore XT chain run - rear derailleur

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Gixxerman

Guru
Location
Market Rasen
I stripped down my rear derailleur on my Trek 8500 to clean it (just removing the chain and jockey wheels only). But I noticed that the chain had been rubbing on part of the derailleur cage. The derailleur cage has a lug about halfway along it's length as shown in picture Chain Run.jpg. When I stripped it, the chain ran to the right of this lug, but this meant that the chain was running over this lug. I have now re-routed the chain so that it now goes to the left of the lug and it clears the lug in all gear positions. I have done this is the chain was causing wear to the lug as shown in picture Derailleur Wear.jpg. You can clearly see that 2 groves have been worn in the lug by the chain side plates. Original chain run was in front of and over the lug in this picture, the new chain run is behind the lug. Was the chain run incorrect before my modifications or has the cage been dismantled and reassembled incorrectly in the past causing the issue? (e.g. the side plate put on back-to-front or upside down). Does the lug have some function?
 

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  • Chain Run.jpg
    Chain Run.jpg
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  • Derailleur Wear.jpg
    Derailleur Wear.jpg
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Cubist

Still wavin'
Location
Ovver 'thill
Likely to have been threaded wrong either on assembly or at some point since. Its easily done.

I'm intrigued that you removed the jockey wheels to clean the mech. That's a level of faff on any bike! The current run in your pic is correct
 
Last edited:
OP
OP
Gixxerman

Gixxerman

Guru
Location
Market Rasen
It wasn't fouling it too badly, so there wasn't a lot of noise. I just noticed it when I stripped the rear derailleur. I removed the jockey wheels to clean and relube them.
 
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