Replacing brake master cylinder

[denefoster]

So, maybe a dumb question but what's required to match up aftermarket M/Cs ? I've got an 09 HUsqvarna SM610 with a dinky brembo builtin reservoir, with a custom lever mount. So no aftermarket levers, no in-country stock I'm guessing, and stupid price/time to get one in if required. Apparently Ducati Monster M/Cs fit.. but how would I know ? And what other models could I look for a replacement from ? Stock piston is 13mm from what I can figure out.. a Brembo 15RCS appears to work fine, but they're a wee bit pricey. Thoughts ?

[FJRider]

So, maybe a dumb question but what's required to match up aftermarket M/Cs ? I've got an 09 HUsqvarna SM610 with a dinky brembo builtin reservoir, with a custom lever mount. So no aftermarket levers, no in-country stock I'm guessing, and stupid price/time to get one in if required. Apparently Ducati Monster M/Cs fit.. but how would I know ? And what other models could I look for a replacement from ? Stock piston is 13mm from what I can figure out.. a Brembo 15RCS appears to work fine, but they're a wee bit pricey. Thoughts ?

I assume FRONT brake reservoir/levers type mounting is what you're after. Depending on the handlebar type (standard tubeular ???) Mounting should not be an issue. Take a bare set if bars (same Dia) to a bike wreckers... and choose one that will look/sit ok.
While you are there ... get a few spare levers too ...

[denefoster]

I assume FRONT brake reservoir/levers type mounting is what you're after. Depending on the handlebar type (standard tubeular ???) Mounting should not be an issue. Take a bare set if bars (same Dia) to a bike wreckers... and choose one that will look/sit ok.
While you are there ... get a few spare levers too ...

Does that mean the cylinder itself does not matter so much ? IE, most M/Cs should work with most calipers, assuming it holds enough fluid to deal with a 320mm rotor ? Essentially I'm after a way to fit aftermarket levers, which I can't do currently.

[FJRider]

Does that mean the cylinder itself does not matter so much ? IE, most M/Cs should work with most calipers, assuming it holds enough fluid to deal with a 320mm rotor ? Essentially I'm after a way to fit aftermarket levers, which I can't do currently.

They SHOULD ... I have built a few "bitsa's" over the years ... most brake lines are interchangable.

Reservoir size matters little when brakes are properly bled... just have to be topped up more regularly.

Take a look in a bike wreckers and ask (not so) silly questions ...

[pete376403]

Diameter is important - ratio between master cylinder dia and caliper cylinder dia matters. If the master cyl is too big, you reduce pressure at the caliper (and gain less travel at the lever), if the master cyl is too small you'll get more pressure at the caliper but have more lever travel

[imdying]

Not so much the diameter, but the swept volume of the cylinder itself. Too big and there's not enough pressure at the caliper, or too little travel which gives no feel, too little and there's insufficient pressure at the caliper, and/or too much lever travel.

[pete376403]

Nup. It is the diameter that makes the difference ie it is the ratio of areas of the master and slave cylinders. Swept volume becomes a function of this. NASA agrees with me: http://www.grc.nasa.gov/WWW/K-12/WindTunnel/Activities/Pascals_principle.html

[imdying]

In practice it's the ratio of the volumes, and reality and experience agrees with me :msn-wink:

[Owl]

I can eat and learn at the same time.

:corn:

[imdying]

Have a look at his link and consider what will happen if you fit a master cylinder with a reduced D1 value. Picking your master cylinder based on diameter alone isn't a good plan.

[denefoster]

Nup. It is the diameter that makes the difference ie it is the ratio of areas of the master and slave cylinders. Swept volume becomes a function of this. NASA agrees with me: http://www.grc.nasa.gov/WWW/K-12/WindTunnel/Activities/Pascals_principle.html

That's exactly what I was looking for. Cheaper than finding some engineering students, buying them drinks and convincing them I just want an equation, not to get busy !

[kwaka_crasher]

Not so much the diameter, but the swept volume of the cylinder itself. Too big and there's not enough pressure at the caliper, or too little travel which gives no feel, too little and there's insufficient pressure at the caliper, and/or too much lever travel.

No. Force is solely the ratio of the diameters. Volume determines travel not force.