Following the fight last weekend to release the bleed screw for Kuroko’s front brake, I rode the bike to the office on Monday. All seemed well at first except the front brake was pulsing: grabbing and releasing. This is often associated with a loose headset, and when I got to the office I had a look at that. The headset doesn’t have any play. I confirmed this on the ride home, where the pulsing only intensified but it was clear the fork was not wobbling in the headset.

The disc rotor and pads are new, and I know from visual inspection that the rotor is not warped. Which leaves: the caliper. I ordered a replacement and it arrived Friday while Nana and I were vacationing in Hakone.

Braking formation

After opening the box of the new caliper, I made a final check that the part number matched the existing one: spot on. The new one looked considerably darker to me, but it might only have been reflecting the black box it was packed in. The photos show scarcely any color difference.

I spent some time getting the tools I needed from the toolbox: bleeding tools, hex wrenches, brake oil, the piston spreader, and so on. I was trying to remember which tool I used to cut the hydraulic brake line when I remembered that I would need the barb press. It took some digging in the tool box to find that, and of course it had the cutting tool for the hydraulic hose attached.

Removal of the old caliper was very straightforward: after removing the new brake pads and setting those aside, I undid the hydraulic line, then two 4mm hex bolts and I was done. With the caliper off and the end of the brake line open, I opened up the bleed screw I’d installed last week. Fluid ran immediately from the open end, so I knew I didn’t have to worry about contamination in the line.

As soon as I inspected the old caliper, I could see the piston had stuck again. While it may be possible to make it serviceable again, for now it goes in the parts bin (a pile, actually). I turned my attention to cutting off the old barb and olive (they’re not reusable) and pressing in the new one. It was a challenge — there is just enough hose left after the cut. And then there was the challenge of getting it all back together and me with only two hands.

Pop!

The bleed block went into the new caliper with ease, unlike the fight I had with the old one. I took my time setting up the bleed kit: cup with fluid and stopper in the top, syringe full of fluid at the bottom. Like a good doctor I worked the air out of the syringe line before continuing — spattering fluid over the floor of the Workshop in the Sky in the process. The moment I loosened the lower bleed screw and put pressure on the syringe, the fluid flowed freely up into the cup at top.

Closing the lower bleed screw and setting aside the syringe, I started pumping the brake lever to work out any bubbles. I was giving a good old squeeze when something went pop! And then fluid was leaking out the bottom. I checked the lower bleed screw and the hose attachment point. All solid. And yet the more I pumped, the more fluid leaked and sprayed out beneath the caliper.

At last I took the bleed block out and had a look. It’s not easy to see, but there’s a hairline crack in one piston. There’s no getting around that and so the new caliper is going back via Amazon returns. I took some time cleaning and boxing everything up — keeping the tools I’d need handy when the replacement arrives — and called it a day.

I’ve got Kuroko waiting in the stand, handlebar turned to give me access to the brake caliper, with a drip tray under the open end of the hydraulic line. I’ve got another barb-and-olive set, but should probably get some more hydraulic fluid. The remaining question is whether there’s enough hydraulic line left for another cut-and-press operation. It will be quite a bit more work to pull a new line.