Worn derailleur pulleys announce themselves through noise before anything else. That ticking sound coming from the rear of the bike often gets blamed on the chain or cassette, but after several thousand miles, the culprit is frequently pulley bearings that have developed play or teeth that have worn into shark-fin profiles. The Y5YC98140 pulley set restores the guide and tension wheels on Ultegra RD-6800 and RD-6870 rear derailleurs to factory condition, eliminating the slop and friction that accumulate with use.

Both pulleys in this set run on precision sealed bearings rather than the plain bushings found in lower-tier Shimano groups. The sealed cartridge design keeps contamination out of the bearing races, maintaining smooth rotation even in wet conditions. When bearings spin freely, less energy gets lost to friction in the drivetrain. The difference becomes noticeable when you compare a derailleur with worn pulleys to fresh ones, particularly in how quietly and precisely the system runs.

The upper guide pulley and lower tension pulley share the same 11-tooth configuration but serve different functions in the derailleur cage. The guide pulley positions the chain laterally across the cassette during shifts, while the tension pulley maintains chain wrap on the cogs under varying chain lengths as you move through the gear range. Both experience constant rotation whenever you pedal, which explains why they wear at a predictable rate based on mileage.... Read More