Which Brembo Radial Master Cylinder?

[mikedxb]

Hi - I’m enjoying my new-to-me gsx s750. However. after my 675 STR, i am not keen on the feel of the front brake.
It has long travel and is quite soft. I don’t think it’s air / hoses / pads as I’ve read it is a common feature due to swapping to nissin four pots and retaining the 14mm axial master cylinder (which may, or may not, be true).
Obviously I have bled the brakes...
As it’s a new toy I’m wondering about a Brembo radial MC.
The RCS 19 seems popular with ability to select 18/20 ratio.
But i wonder if going from 14mm to 19mm is too big a jump and could result in lack of feel / wooden feeling.
I’m not a hard core demon braker, but would like less travel, firmer lever and good feel.
There is a 17mm radial option.
I have not been able to find out the size of the caliper pistons to do ratio calcs.
Any suggestions on what MC may work best for me?!
Thanks in advance.

[Patrick Star]

When the GSR750 was replaced by the GSX-S750 in 2017 one of the major upgrades was the braking system, the Tokico Twin pot calipers were replaced by Nissin Radial 4 pot calipers and standard ABS.

However the master cylinder stayed as an Axial 14mm master, this gave teh 750 a very long soft brake lever. I upgraded the stock Master cylinder on my 1000F to a Brembo RCS so we decided to upgrade my friends GSX-S750 with the master cylinder off the 1000F.

The 1000F has a Nissin 19mm (3/4 inch) Radial Master Cylinder. The 19mm has almost double the area of the stock 750 14mm cylinder reducing the travel of the lever considerably, Being radial gives slightly more rigidity and feel too. Huge improvement to the braking.

https://gsx-s.info/gsx-s750-brake-upgrade/

[catso]

Brembo make a 15mm RCS, still with the 18/20 ratio. I have one on my Guzzi and it's perfect for that, maybe a good option considering you currently have a 14mm?

[Ilikemotorbikes]

If you want a cheap option then fit a 16mm radial master cylinder from a Yamaha R6/R1 or maybe even an Aprilia

You'll pick most up secondhand for sub £75

[Cylon2007]

There's a Nissin Radial MC that is designed for these calipers, they should be readily available on Ebay etc.

[rodericb]

Yeah, grab a Nissin radial MC from a GSXR. The Nissin radial MC from a Triumph might also be the same and the BMW S1000RR too. The Kawasaki versions of the Nissin MC have a slightly different placement of the brake light switch so to make your life easier, just go for the Suzuki/Triumph/BMW. Check the model number of the brake lever to see which is which. This parts list will help: http://www.zeta-racing.com/street/pilot_lever/appl...

If you're going to a radial MC check that you'll have the room as it'll stick out forwards much further that the axial MC. That's what snookered my plans to stick a Nissin MC on my ZX9R - it'd hit the clocks near full lock.

Edit: and you'll need an axial to radial converter. You can get them from HEL.

Edited by rodericb on Monday 8th March 10:25

[mikedxb]

Interesting (and more cost effective) options there- thank you. I seem to recall that some gsxr MCs were subject to a recall? If so, I wonder how to know whether buying a “good” one.

[mikedxb]

mikedxb said:

Interesting (and more cost effective) options there- thank you. I seem to recall that some gsxr MCs were subject to a recall? If so, I wonder how to know whether buying a “good” one.

Update - google says 2004 - 2013....

[smifffymoto]

ISR from Sweden make some nice kit.
I had a master cylinder on my supermoto back in the day.

[mikedxb]

Thank you for the comments and recommendations. Still looking at options and was trying to be a bit more scientific about it. But I have stumbled in that I cannot find the diameter(s) of my nissin brake caliper pistons.... and I have googled quite hard (2018 GSX S750)!
If anyone is more internet (or brake piston dimension) savvy and can find this info... I would be very grateful and very impressed!
Otherwise will take pads out and weekend and see if i can measure them.
Thanks!

[mikedxb]

Persevered.... I think the caliper is the same as B-King, which is 34/30, which is equivalent to 2x32. These figures may not be correct, but it’s the best information i could find on google.

[mikedxb]

So Brembo website says RCS 17 for up to 32mm pistons, and RCS 19 for larger pistons. I posted a question to Capimoto and they kindly replied as above. Think this post is another example of an OP deciding what he wants and then fishing around for validation! On one hand why would i ignore the manufacturer’s advice, but on the other i still have the feeling that rcs 17 would suit me better as i am not after brick wall brakes and want good feel.