July 8, 2026

Goal was to bleed the rear hydraulic on my neighbor's commuter — a Shimano MT200 lever and caliper gone spongy over eight months of wet commuting, lever pulling almost to the bar on a descent.

Set up on the bench with the wheel out and the caliper level. Shimano SM-MM-1 bleed kit: funnel, syringe, genuine mineral oil. Not improvising the fluid — DOT cross-contamination dissolves the seals. Nitrile gloves; mineral oil stains everything.

1. Pulled the pad, inserted the bleed spacer, confirmed both pistons moved evenly.
2. Threaded the funnel into the lever port (7 mm), filled to the line.
3. Attached the syringe to the caliper nipple, hose submerged in oil — backflow stays fluid, not air.
4. Opened the nipple a quarter turn, pressed the syringe slowly upward. Not a pump; a steady push.
5. Lever feel returned around 20 ml throughput. Closed the nipple, removed the syringe.
6. Worked the lever a dozen times, topped off the funnel, waited two minutes.
7. Capped and torqued the lever port to 0.3 Nm.

The failure came at the caliper nipple. I used an open-end 7 mm wrench for speed, and the aluminum nipple turned a half-rotation past expected resistance before seating — aluminum on aluminum, no thread prep. Spec is 4 Nm; I'd delivered five before the seat feel registered. It seals, no leak, but the threads are soft. I'll replace the nipple before this bike returns.

The bleed itself went cleanly. Lever feel is firm and consistent, no sponginess at the top of the stroke. The whole mistake was on the tightening end.

Next time I'd use a flare-nut wrench on that nipple — grabs two more hex faces, slows things just enough to feel resistance change — and I'd torque to 3 Nm first, check the seat, then go to 4.

#workshop #bikemechanic #brakebleed #hydraulic