Problems refilling my brake system

[loply]

Hi folks,

I removed/stripped/rebuilt the calipers on my Mille for general servicing purposes. I've done this before on my SZR (which also has Brembo calipers) so the procedure was familiar.

Upon putting the calipers back on though, I can't get them refilled with brake fluid! I've only ever done this before on single-caliper systems.

I tried firstly the usual routine of pumping and twiddling bleed nipples, which just didn't work somehow.

Then I tried pressurising a container of brake fluid and forcing it up via the bleed nipple... Even at 30psi it wouldn't go though, it just sat there.... No bubbles appearing in the resevoir. I tried various combinations of twiddling nipples and whatnot.

What gives? Any suggestions?

I know people often use a 100ml syringe for this, but I guess that's the same as my pressurised container (which was siphoning the brake fluid).

Any suggestions?
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Yamaha SZR660 Caution to the wind, the throttle pinned!

[loply]

Incidentally folks the reason I was rebuilding my calipers is because on my last ride, the front brake spontaneously applied itself such that I couldn't move the bike!

The wheel literally locked and I was stuck.... Leaving it for 10 mins I could then move a few feet, but it would then lock again.

I diagnosed this as a pad which appears to have fallen out of place, but I'm now wondering if it's a master cylinder issue instead?
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Yamaha SZR660 Caution to the wind, the throttle pinned!

[finpos]

Does sound awfully like the piston it the master cylinder is not returning fully to it's resting position - when it's there the pressurised bit of the hydraulics is open to the reservoir and that's what should be letting you force fill it. If it's not home you've got a sealed system and no amount of pressure will put fluid through there (you might succeed in compressing a bit of air that's lingering in there, but that's it)

f.

[Coxyzxr]

[loply]

Any idea where I can find a diagram of what's inside a master cylinder/resevoir arrangement?

I'm trying to get my head around it but don't exactly understand what's there... I know there's obviously a hydraulic piston, but is there any valves or other such gadgetry?
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Yamaha SZR660 Caution to the wind, the throttle pinned!

[loply]

Should the piston in the M/C return to an "open" position by itself, using some kind of spring?

Just when I had the M/C off, I blew some compressed air through it, and I reached in with a screwdriver and pressed the piston to see if it was seized... It moved freely until it stopped (at the end of its travel), but then it stayed there... As far as I know it still hasn't moved, what will make it return, hydraulic pressure? Is it not going to be blocking the filling process now?
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Yamaha SZR660 Caution to the wind, the throttle pinned!

[Kickstart]

Hi

There is normally a spring inside the master cylinder to return the piston. Normally a tapered coil spring.

Down side is that I suspect Brembo won't sell a rebuild kit and expect you to buy a new master cylinder (Aprilia show them on the parts list but not with any part number, just as part of the master cylinder).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Vincent]

[loply]

Got it solved folks.

The aftermarket brake lever I fitted was not quite identical to the original, meaning the piston was constantly pushed in a tad, and fluid couldnt return.

Filed the armature thing down a millimeter or two and it worked.

Refilled the system using a syringe and several hours of farting around bleeding it through different nipples.

All is well now.

Dangerous shit, those aftermarket levers....
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Yamaha SZR660 Caution to the wind, the throttle pinned!