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I replaced the pulley wheels in my D/A 7800 RD with ceramic-bearing wheels from FSA. I noticed that the original top pulley wheel had 1-2 mm of side-to-side play, while the top FSA wheel has none. Is this play important? If anything, rear shifting seems faster with the FSA wheels.
 

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tantra said:
Is this play important?
Supposedly, the lateral play in the upper jockey wheel assures clean shifts even if the derailleur adjustment is a bit off. So with perfect derailleur adjustment, a jockey wheel without lateral play could well deliver crisper shifts. Be aware that nasty internet wars have been fought over the intended purpose / effectivenes of the patented Shimano "Centeron" upper jockey lateral play feature.
 

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tantra said:
I replaced the pulley wheels in my D/A 7800 RD with ceramic-bearing wheels from FSA. I noticed that the original top pulley wheel had 1-2 mm of side-to-side play, while the top FSA wheel has none. Is this play important? If anything, rear shifting seems faster with the FSA wheels.
You probably replaced a jocket wheel with a bushing, for one with a bearing.

The top pulley on most Shimano systems has a bushing, which does allow a little bit of side-play. It helps correct for some slop in the system if the chain isn't lined up PERFECTLY with the cogs.

With a nice-day or race bike, you should be fine, but I've definitely appreciated this on my commuter... I go through maybe two of those pulleys a year.
 

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JimP said:
The DA top jockey wheel has 2 rows of miniscule ball bearings and will move back and forth 1-2 mm.
All Shimano rear derailleur top jockey wheels have lateral play—doesn't matter if they're running on a plain bearing (often ceramic) or a ball bearing.
 
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