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Well, in over 10 years of riding, racing, and wrenching my own bikes, this is a new one for me. I've been converting my single front rotor 900ssFE cafe racer back to dual. I've got twin brembos (40mm bolt spacing), EBC wave rotors, steel braided lines, and a nissin 5/8 (18-19mm) master cylinder. Bled the system, and the brakes work great. However, over time, the pressure in the system BUILDS UP, rather than loses pressure and needs a re-bleed. Like in the span of 24 hours, the brakes feel fine, minimal travel and then a "solid" feel when the pad engage the discs. Come back the next day, and the front wheel will hardly turn! Almost no travel at the lever! Wierd. Some of my theories -- the stainless steel lines are starting to expand, and then contract and "lock" the system up... could it be the brake fluid? Its not "new", but I've always kept it in a sealed container... maybe on my shelf for 1 year. Wrong rating? Its DOT 4... The way I've got the lines oriented is single from the m/c to the right caliper, and then a double banjo from the right caliper to the left...

Any similar experiences? Any other ideas?
 

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Maybe the bleed hole is being covered in the master cylinder. In other words, you have the piston adjusted too far in when the brake lever is released. That's what can happen when you try to adjust the least amount of freeplay possible into the lever. Doing this will cause exactly the type of thing you are posting about.
 

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What he said. It happens all the time when people put aftermarket levers on their bikes and adjust all the play out of the lever...
 

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I had a similar experience with the hydraulic disc brakes on my geared mountain bike (mmmmmm, titanium....) and the problem was too much fluid in the reservoir. Is your reservoir completely topped up beyond where it should be?
 

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Make sure the m/cyl. cap isn't screwed on so tight that the vent in the cap is blocked.The res. has to be able to breathe and allow for heat expansion of the fluid.If it can't it will cause all sorts of braking problems like dragging and different amounts of lever travel.Check the cap vent while you are making sure the lever is allowing full piston return in the m/cyl.
 
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