Bicycle Mechanics - friction in derailer pulleys

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paul2432
10-15-10, 03:12 PM
I was changing the chain on my bike last night and noticed the top pulley had significantly more resistance to rotation than the bottom pulley. This is a Shimano XT rear derailer.

I took apart the top pulley and cleaned it, and it did not seam to make much difference. Today I bought a new pulley and it too seems to have some resistance.

Is this normal? If so, why does the top pulley have more resistance than the bottom pulley?

Paul

fietsbob
10-15-10, 03:46 PM
shouldnt be so .. those have lateral motion, ? maybe something got out of spec on the sleeve and its binding..

pick up a replacement part.
desertdork
10-15-10, 04:54 PM
On the few dérailleur models I've used (Ultegra, XT, and 600), the upper pulley never spins as freely as the lower pulley. I believe this is due to the former using a bushing as opposed to the bearings in the latter. From your description, unless the bushing is damaged, I don't believe you're experiencing anything unusual.

Chombi
10-15-10, 05:28 PM
I dunno, but most, rear derailleurs I have encountered seems to have quite a bit of lateral play at the pulleys. specially the French Simplex and Mavics. I can't remember though if the Suntour RDs (Superbe Pros) with sealed bearings that I had used had the same play.
Bronze(?) solid bearings work fine if properly kept clean and lubricated (which might be just what you need to do to get the drag out of the top pulley on your RD, if you have not done it.)and I think that ball bearings are most of the time a bit of an overkill for rear derailleur pulleys.

Chombi
duckforcover
10-15-10, 05:42 PM
I think generally, with the ceramic bushing for example, the tolerences on the upper pulley are tighter. My guess is to keep the shifting precise, where as the bottom pulley has to deal with more radical chain angles, thus a little more wiggle room helps.

Under a load, I don't see it making much of a difference.
paul2432
10-19-10, 08:23 AM
I think generally, with the ceramic bushing for example, the tolerences on the upper pulley are tighter. My guess is to keep the shifting precise, where as the bottom pulley has to deal with more radical chain angles, thus a little more wiggle room helps.

Under a load, I don't see it making much of a difference.

This sounds like what I have. The upper pulley is a ceramic bushing. Thanks for replies.

Paul