October 9, 2026

Goal today: replace a worn 11-speed cassette on my commuter and measure chain stretch while the wheel was off — two tasks I'd been deferring for a couple of weekends.

The Park Tool CC-3.2 read 0.75, Shimano's replacement threshold. I hadn't checked in roughly 800 km and it showed. Pulled the cassette with a Shimano lockring tool and a 12-inch adjustable; no chain whip needed since the freehub pawls held. Steps:

1. Removed the rear wheel, seated it in the work stand.
2. Unscrewed the lockring at 40 Nm, lifted off the CS-HG700-11 cassette (11-34 spread).
3. Checked the freehub body for spline notching — light wear on the wider splines, nothing I'd call sharp.
4. Wiped the freehub body with a clean rag, applied a thin coat of grease to the splines.
5. Seated the new cassette, aligned the wide spline, torqued the lockring to 40 Nm.
6. Fitted a KMC Missing Link for the new chain — eye protection on for that snap, habit more than ceremony.

The failure: I assumed the drivetrain was fine because the bike hadn't started skipping yet — and I didn't check. With the new cassette and chain fitted, it skipped on the 15t cog under load on the first test ride. As it turned out, the worn 15t had developed a hook profile that the old chain had quietly conformed to. The new chain couldn't follow the same path. Reinstalling the old chain confirmed it — no skip — which ruled out the indexing and pointed at the cog.

I'll order a replacement 15t; the rest of the cassette has usable life. Next time I'd measure chain stretch at 500 km, not whenever I happen to remember. Ten minutes with the gauge would have bought at least another 200 km and skipped the diagnostic session I gave myself at the end.

#bikemechanic #drivetrain #workshop #maintenance