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In order to reach the tiny relief hole in the bottom of the stock master cylinder, I had to soak it in clean fluid overnight to soften the gunk and old crystallized fluid. After removing the reservoir and o ring to clean thoroughly underneath the reservoir. I had a rebuild kit on hand, and all new parts-everthing was replaced.
The next challenge was to get the gunk out of the hole proper. I accomplished this by using a tightly fitting drill bit in the outer hole, by hand to get as far as I could without removing any metal. Lots of black gunk was got at this way.Then I very gently spun the drill under power, to counter sink the tiny hole, creating a beveled bottom with the pinhole in the center. Before I did this I could not get the very fine cleaning wire into the hole.There was just enough irregularity from corrosion to prevent it. After the countersink, it was easy.Remove only a very small amount of aluminum, just enough to create a shallow bevel to guide the cleaning wire.
I had trouble until I found a wire small enough. The one I used measured.06 mm diameter. That is .00236 inches. It was a strand from some aircraft cable. My first attempts were way too big. Find the finest strand you've got. I now keep a few strands in my road kit, just in case.
After it is assembled, filled and bled, leave the lever taped down and the handle bar turned so the master cylinder bore angles up toward the reservoir overnight,to get the last fine bubbles out. They will naturally rise in the lines, and leaving the lever compressed keeps the valve open, allowing them to escape into the reservoir.
Do a final bleed before testing the brakes. I learned (the hard way)to leave the bike in the sun for an hour or two.The heat will cause the fluid to expand- if the relief hole is now clean, the expanding fluid will escape into the reservoir, and the brakes will function normally. If the hole is still blocked, the brakes will lock. In which case, repeat. Doing it this way avoids finding out the brakes lock while riding it. Duh
Go slowly to be safe, and be alert for signs of binding brakes for awhile until reliability and safety are certain.
Please add your wisdom- a collection of ideas for this job in one thread is a good thing!
The next challenge was to get the gunk out of the hole proper. I accomplished this by using a tightly fitting drill bit in the outer hole, by hand to get as far as I could without removing any metal. Lots of black gunk was got at this way.Then I very gently spun the drill under power, to counter sink the tiny hole, creating a beveled bottom with the pinhole in the center. Before I did this I could not get the very fine cleaning wire into the hole.There was just enough irregularity from corrosion to prevent it. After the countersink, it was easy.Remove only a very small amount of aluminum, just enough to create a shallow bevel to guide the cleaning wire.
I had trouble until I found a wire small enough. The one I used measured.06 mm diameter. That is .00236 inches. It was a strand from some aircraft cable. My first attempts were way too big. Find the finest strand you've got. I now keep a few strands in my road kit, just in case.
After it is assembled, filled and bled, leave the lever taped down and the handle bar turned so the master cylinder bore angles up toward the reservoir overnight,to get the last fine bubbles out. They will naturally rise in the lines, and leaving the lever compressed keeps the valve open, allowing them to escape into the reservoir.
Do a final bleed before testing the brakes. I learned (the hard way)to leave the bike in the sun for an hour or two.The heat will cause the fluid to expand- if the relief hole is now clean, the expanding fluid will escape into the reservoir, and the brakes will function normally. If the hole is still blocked, the brakes will lock. In which case, repeat. Doing it this way avoids finding out the brakes lock while riding it. Duh
Go slowly to be safe, and be alert for signs of binding brakes for awhile until reliability and safety are certain.
Please add your wisdom- a collection of ideas for this job in one thread is a good thing!
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