Modern Master Cylinders are a PITA to bleed!

[81xsproject]

I finally got my more modern, '99-'00, Nissin master cylinders mounted and am in the PAINSTAKING process of bleeding them. On a side note, don't waist your money on the vacuum bleeder from Harbor Freight. It lasted ONE use and then it lost its seal. Anyway, the modern masters don't allow the use of vacuum bleeder anyway because they don't leak at all. They seem to only move fluid when the plunger is moving. Is there some trick beside the standard bleeding procedure that I don't know.

[petejw]

Hey 81,
Did you bleed the master cylinder first?
Fill the master cylinder with brake fluid,
press the lever in, then block off the outlet with your finger to prevent air being sucked back in, do this a cpl of times to get the air all out,before bleeding the calipers.
This can be done on the bike or on the bench, just be careful of brake fluid being spilt.

[Ivan]

You might try cracking the bleed screw and letting it gravity feed, I know you said it won't move fluid with out moving the plunger, but I haven't run across a master cylinder yet that doesn't have a return port (spooge hole). Your piston may not be retracting fully, so this may not work.

The other method I use is to apply gentle pressure to the end of the bleed screw with a finger. Enough that the fluid can escape, but not let any air in, just like a check valve or speed bleeder. Then I have an assistant pump the living crap out of it until I stop getting bubbles. It could possibly be a one man operation on the scoot. When Chevy started putting hydraulic clutches in their trucks, they were notoriously hard to bleed. Since the line went about a foot above the MC, this is the only way I could get them to bleed without taking two hours.

At one point in time I had a piece of plate aluminum with a schrader valve in the middle, and a piece of inner tube rubber for a gasket. I held it in place with hose clamps or a c clamp and used a bicycle tire pump to pressurize the reservoir and push fluid. It was a quick and dirty pressure pot type setup, but I had to be very careful not to run it dry. It would empty the system of brake fluid in a hurry if I weren't careful.

Believe me, I know how friggen frustrating brakes can be.

[81xsproject]

I found the trick. I pushed the slaves closed and I could here tons of air bubble up out of the master. After that it was a breeze. The clutch master was much smoother. I got a long piece of hose and applied some suction to the bleeder while I pumped the lever. After that, it went like I should.

[John]

See post #10

http://www.xs11.com/forum/showthread...verse+bleeding