Front master cylinder size

[pgnz]

rigged my xs with vfr calipers which originally are 3 piston slider type  with the 4 outer pistons connected to the front
 12mm master with the 2 smaller middle pistons connected
 to the vfr rear brake master and twin piston rear caliper
which is connected to the front outer piston circuit via steel lines
with spring-loaded ball bearing valves which creep open at certain pressure to connect to the front middle pistons when using the rear brake and the other way around when using front brake- the sprung-ball valves opening being determined by amount of pressure applied at either brake lever...

 So ditched the linked system setup by removing/plugging-off the valved rear brake line connections and drilled a 2mm hole inside between front caliper middle pistons and the outer 2 pistons' circuit so then having all 6 front pistons
 on the same circuit and all connected to the front master only..
  but with the extra 2 middle pistons added to the 4 outer pistons
 the 12mm master became way to soft and weak, so ditched the vfr master and tried the 17.5mm xs master and by fluke was perfectly suited with the brakes instantly becoming super-powerful with super-duper feel and control.. 
Yeah not complicated at all...

[pgnz]

17.5 mm cylinder for the ancient old clunky xs single piston slider calipers, but which when scrubbed gleaming clean throughout and with steel lines are still lacking real bite and are always gonna be weak compared to opposed 4-piston bluespots and a myriad of other better stuff available out
there at the bike-wreckers.

Even my ancient old clunky suz gs1000 had way better brakes than the poor xs11's anemic setup.  Highly likely in the 70's the yamaha xs11 engineers were drunk and stoned and hungover from extra-strong sake the week they were asked
 to design the xs's brake system.

[Primate]

Hey Roger thanks for that info , so I have purchased a16mm piston master cylinder and I have actually managed to get the calipers to work so im happy with things so far,  next issue is the oil leak from the main bearing behind the vacuume advance 
quote a :Duthor=Roger link=topic=3491.msg24711#msg24711 date=1618360550]
Hi Tarn,
I did a bit of homework a couple of years ago for putting blue spots on a sidecar project and stumbled across this info from a vintage brakes blog site somewhere - might be useful. There are a few variables to consider.
http://www.vintagebrake.com/mastercylinder.htm was the original post, but no longer available, so I have included some info below. A search around various blog pages gives a whole range of other anecdotal and technical info and some of it conflicting!

Extract from original blog.
While attending Vintage Days West, and thoroughly enjoying it, I was reminded that many of the people I had occasion to talk to, lacked an understanding of the importance of master cylinder to wheel cylinder ratios. This critical ratio is of paramount importance in determining "feel". It has been my experience that there is a "sweet spot" in the range. I like ratios in the 27:1 range - 2 finger power brakes, feeling some line and/or caliper flex. 23:1 is at the other end of the spectrum - firm. Ratios lower than 20:1 can result a feel so "wooden" as to have a toggle switch effect: nothing happens until the wheel locks. Disc and wheel diameters must be taken into consideration. A 10 inch disc working against a 19" wheel just doesn't have the leverage ratio that a 13 inch disc working a 17" wheel does. The hand lever ratio counts too: witness the adjustable master cylinders from Lockheed and Brembo.
A case in point: I had a complaint from a racer about Ferodo CP901, a compound renowned for its great feel. His comment was that they worked poorly until the wheel locked. He had been thrown on the ground twice. Intrigued, I inquired as to the application. "Yamaha RD350" he replied. A red flag went up. CP901 was not available for the 48mm Yamaha caliper. I asked "How that could that be?" He had up-graded his braking system with the 41mm Lockheed unit, but was unaware that a master cylinder change was in order. A stock RD 350 has an already poor ratio of 18.3:1, and with Lockheed, became an unhealthy 13.3:1. The "sweet spot" formula said a change to a 11 or 12mm master cylinder was in order: my personal preference and recommendation would have been an 11mm. He was able to switch to a 1/2", and although not ideal, he was keeping the rubber side down.
For 2 piston opposed calipers, I like ratios in the 27:1 range, feeling some line and caliper flex. For a firmer lever, use 23:1. I think ratios lower than 23:1 produce a lever feel so "wooden" as to have little, if any feel. Combine "low" leverage ratios with sticky pads, and unpredictable lockup is the result. The high effort required at the lever also results in undesired input to the bars. Single piston calipers are much happier in the 14:1 to 12:1 range. Disc and wheel diameters, as well as hand lever ratios, must be considered. Chart attached.

There is nothing written on the outside of my M/C but I think I ended up choosing a 15mm. The project hasn't hit the road yet, so only tested in the shed, but the "feel" and travel of the lever seems about right with braided lines and blue spots (4 pistons 2 X 26mm, 2 X 30mm). Two finger braking should be possible.

Good luck
Cheers
Roger

[/quote]

[Roger]

Hi Tarn,
I did a bit of homework a couple of years ago for putting blue spots on a sidecar project and stumbled across this info from a vintage brakes blog site somewhere - might be useful. There are a few variables to consider.
http://www.vintagebrake.com/mastercylinder.htm was the original post, but no longer available, so I have included some info below. A search around various blog pages gives a whole range of other anecdotal and technical info and some of it conflicting!

Extract from original blog.
While attending Vintage Days West, and thoroughly enjoying it, I was reminded that many of the people I had occasion to talk to, lacked an understanding of the importance of master cylinder to wheel cylinder ratios. This critical ratio is of paramount importance in determining "feel". It has been my experience that there is a "sweet spot" in the range. I like ratios in the 27:1 range - 2 finger power brakes, feeling some line and/or caliper flex. 23:1 is at the other end of the spectrum - firm. Ratios lower than 20:1 can result a feel so "wooden" as to have a toggle switch effect: nothing happens until the wheel locks. Disc and wheel diameters must be taken into consideration. A 10 inch disc working against a 19" wheel just doesn't have the leverage ratio that a 13 inch disc working a 17" wheel does. The hand lever ratio counts too: witness the adjustable master cylinders from Lockheed and Brembo.
A case in point: I had a complaint from a racer about Ferodo CP901, a compound renowned for its great feel. His comment was that they worked poorly until the wheel locked. He had been thrown on the ground twice. Intrigued, I inquired as to the application. "Yamaha RD350" he replied. A red flag went up. CP901 was not available for the 48mm Yamaha caliper. I asked "How that could that be?" He had up-graded his braking system with the 41mm Lockheed unit, but was unaware that a master cylinder change was in order. A stock RD 350 has an already poor ratio of 18.3:1, and with Lockheed, became an unhealthy 13.3:1. The "sweet spot" formula said a change to a 11 or 12mm master cylinder was in order: my personal preference and recommendation would have been an 11mm. He was able to switch to a 1/2", and although not ideal, he was keeping the rubber side down.
For 2 piston opposed calipers, I like ratios in the 27:1 range, feeling some line and caliper flex. For a firmer lever, use 23:1. I think ratios lower than 23:1 produce a lever feel so "wooden" as to have little, if any feel. Combine "low" leverage ratios with sticky pads, and unpredictable lockup is the result. The high effort required at the lever also results in undesired input to the bars. Single piston calipers are much happier in the 14:1 to 12:1 range. Disc and wheel diameters, as well as hand lever ratios, must be considered. Chart attached.

There is nothing written on the outside of my M/C but I think I ended up choosing a 15mm. The project hasn't hit the road yet, so only tested in the shed, but the "feel" and travel of the lever seems about right with braided lines and blue spots (double sided - 4 pistons 2 X 26mm, 2 X 30mm). Two finger braking should be possible.

Good luck
Cheers
Roger

[AussiXS11G]

hey Tarn
there is nothing wrong with the OEM calipers as long as they are in good nick - with braided lines you will easily lock them up
the only thing missing is "feel" and that is the difference with the blue spots

[XSIIE]

I use the FZR 1000 MC as a replacement. Works on original brakes and the Bluespots 100 bucks from wreckers

[Primate]

Thanks guys , oh the joys of impulse buying I have ordered a set ( brake and clutch ) as it would do my head in having miss matched leavers on the bike . And ill look to get a cheap master cylinder to get her rolling for now as the other set is a month away and im chafing at the bit to get her rolling befor then . (Patince is not my strong suit 😄) . Thanks again for all your help

[Christian Raith]

As discussed 🙂🙂

[Jonesy :-)]

Primate, standard front master is 11/16" pretty, darn close to 18 mm, so your 12.7 mm is way under size

[Primate]

Hey Brian
Thanks fot that info i was thinking of loosing the splitter
And using a double banjo but after reading about the blue dot brakes that a lot of you guys are using im inclined to just get these running for now and upgrade the whole shooting match down the line .

[AussiXS11G]

hello Tarn
I found a similar problem back in 2003 when I started modding mine - still the stock calipers and rotors (re-kitted and surfaced)
I did away with the splitter and fitted 2 equal length braided lines from the master and  I fitted a 1997  Kawazaki ZXR750R front master which I am still using now with the R6 front setup (I've been too lousy to buy the recommended Brenbo master)
I did research the piston diameters of the masters at the time but the details now escape me.

hope this helps
Bryan

[Primate]

Hey ho here we go ,
Well things are moving along well on my hack rod build  but I still can't get any decent pressure from the front brakes, leaver pulls all the way to the bar ,the brakes are engaging but with no real power I would not be confident in them to pull up a hack . History the callipers have been full stripped down and new seals fitted with braided hoses installed, and I have an new ebay master cylinder up top and still using the original splitter again its been fully stripped and cleaned out . I have bleed them the standard way with no great results and with the help of Christian's vacume kit with the same results . I am wondering if the master cylinder I bought from ebay has the wrong pistion size (Piston hole size: 12.7mm) if any one knows what size the standard bore should be or has any advice I would be eternity grateful.  Cherrs Tarn