Yamaha TRX850 Enthusiasts Forum

Copied from the tyres thread

johnners987 wrote:....
As it is I've got front brake master cylinder issues at the moment so I've got time to think while I resolve that..... I appreciate it's completely off topic but 6 pot calipers and a 14mm master cylinder doesn't seem a good mix......
Cheers

I have the same question

I have 6 pot YZF callipers which are pretty good for stopping power, but there is a heck of a draw on the brake lever. I am using the 5/8 master cylinder and was going to try the 14mm one that goes with the blue spots, but sounds like that may not be a runner.

Anyone else running the 6 pot YZF callipers had similar issues or found a solution to the long draw on the 5/8 master?

I had a YZF750R and with the original setup the lever always seemed a little loose, a lot of leverage before actual braking action. In fact, I have never seen any YZF750R with tight brakes.
I think this is because of the six pots, needing a siginificant amount of braking fluid to be displaced.
Things might be better with a bigger diameter master cilinder, instead of smaller. A 18 or 19 mm radial Brembo, for example.

I used to use -2 lines with Toki 6 pots, lots better.

Better work out the ratios!

What diameter are the pistons in the caliper? You can work out what your ratio should be from here:

http://www.vintagebrake.com/mastercylinder.htm

M.V. wrote:Better work out the ratios!

What diameter are the pistons in the caliper? You can work out what your ratio should be from here:

http://www.vintagebrake.com/mastercylinder.htm

This is good but I'd just like to say if you're looking to use a radial m/c go with something larger as the pivot is a bit further away so the lever moves a bit more. Using the 27:1 ratio as suggested by the site lead me to a 11/16 m/c but being radial I have a lot of free play at the lever. Phenomenal when it does bite though!

Snod Blatter wrote:
This is good but I'd just like to say if you're looking to use a radial m/c go with something larger as the pivot is a bit further away so the lever moves a bit more. Using the 27:1 ratio as suggested by the site lead me to a 11/16 m/c but being radial I have a lot of free play at the lever. Phenomenal when it does bite though!

Agreed on this (as far as I've got) although more through trial and error than calculation. Currently using an 11/16 (approx 17mm) radial m/c off a Fireblade but there is indeed a lot of play at the lever. Also the m/c is so bloody bulky that it fouls the engine cut out switchgear and rotates the cut out switch under the throttle cables. Looking to source a (slim!) 19mm (3/4) m/c but best do the calculations first this time eh?

The diameter of the pots is 27mm and 25mm. I used a Brembo 19mm pump.

baverhae wrote:The diameter of the pots is 27mm and 25mm. I used a Brembo 19mm pump.

Cheers all. Just back from holiday so I've still got this to sort. From the comments so far I assume that the standard 16mm YZF750R m/c has acceptable 'throw' because it is not radial? Personally I'm not too bothered about going radial and a standard 16mm would be acceptable (but muggins also thought the radial 17mm Fireblade would be ok)
The 19mm Brembo m/c is undoubtedly not cheap(?) and I've got to get costs under some semblance of control as I've still got damn insurance, MoT and tyres to sort (yes, still got to decide on rubber..........)
Can anyone confirm the standard 16mm is a viable alternative and works/ fits given my earlier issues with the Fireblade m/c? Again, my assumption is that it worked fine on the 750 and the throttle cable routing looks similar to the TRX......... and it's a cheaper alternative to the Brembo.

Notwithstanding the earlier comments (clearly I wasn't paying attention) I've gone with the 5/8ths master and everything seems fine. Two brake lines and a Pazzo lever and it feels like a nice firm lever action with just the right amount of feel/ movement - seems very similar to my R1. All in all very happy given I've also resolved my binding rear brake too so a good day! Time to get some miles on........