October 30, 2026

Goal today: bleed the rear hydraulic brake on a neighbor's gravel bike — lever had gone spongy enough that full-finger pull gave her almost no modulation on a descent. She's planning a group ride next weekend and asked me to look at it before then.

The brake is a Shimano GRX 810, mineral oil system. I prefer mineral oil over DOT fluid because it doesn't strip paint and I stopped labeling rags for that job years ago. Pulled up the Shimano procedure I keep printed in a page protector in the binder above the bench — I've done this brake three or four times now, but I still read it through before I start.

1. Removed the rear wheel, hung the caliper level with a rubber band around the rotor slot.
2. Unscrewed the bleed port bolt at the caliper — T10 Torx, which I nearly stripped once using a worn-down bit. New bit lives in a labeled spot now.
3. Attached the drain syringe to the caliper port, opened the lever clicker, removed the lever port screw, attached the fill syringe with fresh mineral oil.
4. Pushed from the lever downward, watching for bubbles in the drain syringe.

The failure was entirely mine. Step 4 — I pushed the lever syringe before I had the drain syringe firmly seated at the caliper. Oil came back out past the fitting, ran down onto the brake pad face. Rotor-contact side. I caught it fast but not fast enough. Wiping mineral oil off a resin pad is not a real fix; I swapped the pads, pulling a spare set of L05A-RF resin from the shelf where I keep them for exactly this reason. Wrote it in the log: "seat caliper syringe first, every time, no exceptions."

Bedded in the new pads with ten slow wheel spins and light lever squeeze each side. Lever feel came back — firm, good progression from start to full pull.

Next time I'd clip the drain syringe on before I even open the lever port, even when I think it's already seated. The thirty seconds of double-checking costs nothing.

#bikemechanic #workshop #hydraulicbrakes #diy