Delinking brakes

[dxhall]

I’m rebuilding an SPIII.  I want to de-link the brakes, but am tempted to cheap out and use the stock rear master cylinder with a later 32/30mm caliper from an EV.  The stock MC is 15mm bore.  I don’t know what the stock MC size was on the EV.  Any sense for what the pedal travel will be? 

[Caffeineo]

This may help.....a chart showing different combinations of master cylinder piston size and wheel cylinder piston size to get good brake feel.
http://www.vintagebrake.com/mastercylinder.htm

[dxhall]

That’s an interesting table.  Would you use the same “sweet spot” number for the rear?

[guzzista]

The 15mm master cylinder is actually 5/8 or 15.875. With the  front brake line plugged off, the pedal stroke will be very short regardless of which caliper.  As the force applied by the foot is strong(er than a hand) , it might work OK  for you anyway.When I delinked my LM1 I used one of those below. The original cap with the switch swapped in IIRC , and  the lever pivot was turned around  as well as new way to hook up the return spring. . The feel was lighter due to the 1/2 inch master bore which is what I was looking for

https://www.ebay.com/itm/363298063045?hash=item54964082c5%3Ag%3AFcEAAMXQ56ZR%7ECQj&LH_ItemCondition=1000

[Dukedesmo]

I also used the above mentioned master cylinder from a same era Italian (Ducati, Laverda etc.) on my de-linked LM2 as it fits (with some slight modification) and works just right on a de-linked rear due to the smaller piston. I didn't bother with the fluid level cap as it just seemed unnecessary.


I used a 15mm master at the front to power both front brake calipers and, again that's the perfect ratio IMHO.   

[dxhall]

Thanks for the help.  I’ve ordered the one from eBay - that should be better than the stock setup or the modern MCs with the different mounting arrangement.

[Dukedesmo]

If the mounting is the same as a LM2? then you will need to lightly modify it to fit as it sits 'backwards' compared to the 'Ducati fit'. Basically need to alter the counterbore in the holes and make some spacers IIRC but, otherwise it is perfect not least because it is the same design as the original.

[Dukedesmo]

With regards to the mods required, here is some more info;   https://wildguzzi.com/forum/index.php?topic=91902.msg1451175#msg1451175