I've been building up a new road bike, and was lucky to find a decent deal on an Ultegra 6600 groupset. In preparing to mount the rear derailleur, I noticed that the guide pulley had considerably more rotational friction than the lower tension pulley. The Ultegra guide pulley is a ceramic bushing system, while the tension pulley is a sealed bearing system. I decided to disassemble and relube the guide pulley, but after doing so, it really had no effect on the rotational friction. It was still much higher than the lower tension pulley.
After thinking about the design, and comparing it to Shimano's other lines, I'm nearly certain the culprit is the friction between the metal dust caps and the rubber seals. When the guide pulley turns, the ends and sides of the dust caps rub against the rubber seals, causing rotational friction. Of Shimano's top three lines (DuraAce, Ultegra, and 105), only the Ultegra derailleur has the rubber seals on the guide pulley. My other bike, with Shimano 105 guide pulley (also bushing), has no such friction. I googled the issue, and although there is not much, there are a few forum threads where people mention the same issue. None, however, really get at the heart of the issue.
Here's a link to Shimano's technical document on the subject, if anyone is that curious:
I don't think this issue has to do with preload vs. no preload, as there is normally not much load on the guide pulley.
My questions are:
Can others confirm if the higher guide pulley friction on the Ultegra is normal? Would love to hear from some professional bike mechanics, who handle alot of these things and have experience to compare their findings.
Do the seals eventually "break in" and lessen their frictional effect?
Would you recommend swapping out the guide pulley for one with sealed bearings? I've heard of a few people doing this and saying it worked great, eliminating the drag, but I'm wondering if there is a reason for this drag on the pulley that I'm missing.
And, why would Shimano put a sealed bearing on the tension pulley, and a ceramic bushing on top? Why not two sealed bearing pulleys?
I realize this might sound like an esoteric issue, but it kind of bothers me to put this kind of unnecessary drag on my drive train. Appreciate any wisdom you folks could lend to this matter.