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RD pulley sliding off center?

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RD pulley sliding off center?

Old 07-07-13, 02:37 PM
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RD pulley sliding off center?

On two occasions now, I've noticed my lower RD pulley (Ultegra Di2) sliding to one side on its bearings. I think it happens because of cross-chaining. (Di2 encourages cross-chaining and, on top of that, I'm running a crankset with nonstandard chainline.) When it happens, my chain ends up rubbing against the derailleur cage because it's off-center. It's easy to put back in the middle (I push on the pulley with fingers and it clicks back into place) but I'm wondering if I need to replace it or if something else is wrong.

And, on a related question, the upper pulley does not spin freely. I took it apart and it appears to be by design (there are no ball bearings, just a few parts rubbing against each other). I greased everything generously but it still won't spin as easily as the lower. It seems inefficient. What's the deal with that?
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Old 07-07-13, 09:27 PM
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Ultegra (Centeron, ceramic bearing) upper pullies have had far greater friction than the lower (ball bearing) pully since the 6500 gruppo arrived in 1997.
I used to oil the seals before each race.
Grease isn't supposed to be used in the ceramic pully bushing, but thin grease should be ok.

Dura Ace top pullies have (since 1997) used a sophisticated floating ball bearing system with two rows of tiny balls rolling directly on a cylindrical sleeve, and with good seals to boot. These cost almost $40 each, but might be a good idea for racing use.

As far as the cross chaining causing lateral displacement, are you sure the indexing is adjusted properly?

How is your crankset's big ring sighting down with the cassette? Shouldn't be more than a couple of cogs away from center.
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Old 07-08-13, 01:04 AM
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I don't know anything about Di2 but I do know the tension pulley should not have any lateral movement. The fact that the pulley snaps back into place when pushed tells me something is wrong; you may want to check the tension pulley orientation. From the Ultergra 6770 series Di2 manual;
∑ Periodically clean the derailleur and lubricate all moving parts and pulleys.
∑ If gear shifting adjustments cannot be carried out, check the degree of parallel of the rear
∑ If there is a large amount of play in the pulleys which causes worrying noise while riding,
replace the pulleys.
∑ The tension pulley has an arrow on it to indicate the direction of rotation. Install the tension
pulley so that the arrow is pointing clockwise when looking at the pulley from the outside.
At the very least I would remove the lower pulley and do some maintenance and look to see if it looks worn off the bike. If it pulley doesn't look worn but continues to slide out of place, I would replace the pulleys anyway; a set of pulleys is less than $20 and it will most likely solve your problem.

Edit: As far as the difference in pulley drag between the upper and lower, this seems to be a universal complaint (at least I see it all the time in these forums). I believe the upper pulley does not have sealed bearings due to Shimano's Centeron technology. I may be wrong here but I believe they use the ceramic pulley design because their Dura Ace sealed bearing pulley with lateral movement are very expensive; all the aftermarket sealed bearing upper pulleys I have seen for Shimano derailleurs do not have any lateral movement.

Last edited by onespeedbiker; 07-08-13 at 01:43 AM.
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