Clunk In Ultegra Drivetrain
On one of my bikes I have an Ultegra SL drivetrain. Great drivetrain, shifts as smooth as Dura Ace and I couldn't be happier with it. Well, two weeks ago I developed a clunk that occured after soft pedaling or coasting and then putting power to the pedals again.
First thought was the RD was out of adjustment, and the chain was skipping (new Dura Ace with less than 300 miles on it). I adjusted the RD several frustrating times (on the road) and the clunk was still there.
Second thought was the chain, so I put another chain on it. No joy.
Next thought was the bearings were loose in the bottom bracket (known problem with Madones) but this one has 2600 miles on it and I have checked the BB before. By the by, it is a good idea to occaisionally check the torque on the left side pedal screws on Hollowtech cranks. They can loosen up, although this one never has.
Next thought was the cassette (13/25 6600 Ultegra), but it only had about 1200 miles on it. Anyhoo, I changed it out with another 12/25 I had. Still no joy. Changed again to another 11/25 and same problem.
Finally, after swapping rear wheels (original was Race Lite) with the other Madone (RXL), the clunk disappeared. I came to the conclusion it was in the freehub. I disassembled it, cleaned it up and took the pawls and spring off. I noticed the spring was misshapen at the opposite end from the hook. I bent it back to a round shape again, regreased everything and reinstalled the freehub and life was good again.
This freehub had been noisy from day one. It ticked very loudly. When I disassembled it, there was plenty of grease, but because of the misshapen spring, only one or two pawls ever made contact, the third one lay flat in the pocket. After reshaping the spring, all three had good spring action and stuck up as they should.
What is the moral of this diatribe? Just wanted to give some info to others.
Last edited by richard_dupp; 08-30-12 at 11:58 AM.