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CB550F Double Disc's

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Trigger:
Have a question that someone out on the forum may be able to answer. Fitting double disc's to a CB550, why does everyone state that you need a master cylinder with a larger reservoir? This reservoir holds less fluid than a standard cylinder but, is a replacement for a GL1000 with twin discs.
http://www.ebay.co.uk/itm/Front-Brake-Master-Cylinder-For-Honda-GL1000-GL1100-GL1200-GL1500-Handle-Bar-New-/321185608547?pt=UK_Motorcycle_Parts_13&hash=item4ac8277363

Could anyone explain who has done a disc conversion. Cheers

LesterPiglet:
I don't think it's because of the larger capacity, it's because the MC piston bore is a different diameter.

Johnwebley:
it is due to the fact that you are pushing double the amount of pistons !! and double the amount of fluid,
the standard mastercylinder  may not be able to fully extend the pistons,

so a larger bore M/C is required to ensure both caliper pistons are pressed on the discs with plenty of handlebar lever clearance,

apart from the equation of dia X volume = mech advantage etc,

to much blinding with science !!

yes,it is much better to get a twin disc mastercylinder,

Trigger:
OK, now i am scratching my head, because i have measured up the bore size on the CB550 cylinder and it is 14mm. Matched this up against the cylinder on my CX500 (which is twin disc) and that is 14mm. I must point out that the cylinder on the CB550 is one of those aftermarket jobies from DSS and NOT OEM. Another confusing thing is a rear brake cylinder (though Japanees) states 1/2 inch, which is 12.7mm.   

Trigger:
Cheers Oddjob, that will explain it. All down to caliper piston size then. I will have to sit down and do the maths on this one, because the master in the link above states that it also has a 14mm dia. Trying to work out if the OEM master on the CB550 had a smaller dia piston in the master. ::)

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