Master cylinder/slave cylinder ratios

[Joycie]

Call it the fog of war or just a Christmas hang over (One could argue they are the same) what ever the cause I've a question regarding mechanical advantage as it relates to hydraulic ratios & my brain refuses to compute no matter how many graphic examples I google.

So I found a flash as Brembo clutch master some time ago to match my RCS brake master and jumped on it without question to go on my gsxr 7/11 oil boiler. Now I have fitted it, I've spent three bloody days bleeding both master and slave cylinders. I did find the bleed nipple on the slave had the hole at the bottom of the nipple crushed and as a result had deformed the bottom of the nipple not giving a proper seal when screwed in. The nipple has been replaced and the whole system bled again.

Now I've put another 250ml ($20) through this thing to no avail. I've got good positive feel at the lever but not enough travel at the actuator rod. I've one of those cheap sprocket cover/slave cyl. mounts which gives a good view of the clutch actuator rod and the crap flung off the sprocket gives a very clear/handy witness mark of the extent of travel on the clutch actuator rod. I do have travel at the actuator rod but not as much as I had before replacing the master cylinder.

I feel the system is bled so that has me now questioning my (poor?) selection of master cylinder. Have I screwed up the ratio?

So correct me if I'm wrong the standard gsxr 1100 master cylinder has a 14mm piston and a 36mm slave cylinder piston. 36mm/14mm=2.5mm
Now I've introduced a master cylinder with a 16mm piston into the mix and the standard 36mm slave cylinder piston. 36mm/16mm=2.25mm

Now I can't tell what 0.25mm is by eye but the above tells me that there would not be as much travel at the slave cylinder using a larger master cylinder. There would be less effort required at the lever but still less travel.

Is this theoretical difference, being so small, negligible? I mean this size master is sold to be used on something.

I've searched the big four Japanese manufacturers and have not found a clutch slave cylinder bigger than the 36mm that is already on there. To retain the standard ratio using the 16mm master I'd need a slave of 40mm (40mm/16mm=2.5mm). Getting a custom slave made is pretty drastic and may be a challenge due the lack of realestate in that area ( outside Dia. of the standard slave housing isn't much more than 40mm).

Is anyone else out there using the brembo RCS 16mm clutch master? If so on what?

Hopefully I have over looked something and do not require another slave to work with the new master. Any help would be appreciated.

[xa-mont]

i think you might have it ass about. as far as i understand it, for 1mm of travel on the slave you would need to only move the 16mm master 2.25mm vs 2.5mm on the 14mm. Therefore you should have MORE movement with the 16mm master (assuming the same amount of stroke is available.)

[Joycie]

I sure hope your right. Every time I look at this I come up with a different answer, then I have a(another) beer(s) in celebration of conquering the problem and then in creeps the doubt and I convince my self otherwise.

Maybe I should try a stint in the garage without beer, but that hardly sounds like fun.

[Simo74]

You need to base your calculation on the area of the piston not the diameter.

You had a 14mm master with a 36mm slave so the movement ratio calculation is (14/36)*(14/36)=0.15 This means that the slave cylinder piston will move 15% of the movement of the master cylinder piston.
you now have a 16mm master with a 36mm slave so the new movement ratio is (16/36)*(16/36)=0.197 so your slave cylinder piston will move 19.7% of the movement of the master cylinder piston.

In short you now have nearly 5% more movement at the slave so should be better not worse.