So earlier in the week I startedthis thread about whether I could swap a short cgae from a busted Ultegra derailleur onto what had been a long cage 105
Well the swap is going to work just fine and was actually really easy to do. But the process of tearing down both dearilleurs revealed some differences between the two that help explain cost, weight and quality differences between 105 and ultegra (which I always wondered about since I ride both and never really noticed appreciable performance difference).
1. Ultegra uses lighter pivot bolt. The ultegra bolt is hollowed out while the 105 bolt is solid.
2. Ultegra uses better seals to keep dirt out: There are rubber o-rings around the head and middle of the ultegra bolt. 105 bolt has a plastic collar around the head an no o-ring in the middle (although there is a groove where an o-ring could be added).
3. Ultegra uses better springs. All springs in the Ultegra derailleur are heavier duty than those on the 105.
4. Jockey wheels on Ultegra are higher quality -- they just feel more substantial and roll more smoothly.
So there you have it, just some observations from tearing down rear derailleurs to their nuts and bolts. All parts seem interchangeable so once I rebuild, I will have a Shimano 10tegra 6000 (6500+5500/2) rear derailleur.