I fitted a Nissin CBR 600RR master cylinder to my SuperHawk about a year ago. One thing about this m/c baffles me. There is a rectangular piece of what appears to be styrofoam called a "float" that sits inside the reservoir and "floats" in the DOT4. I've bled a bunch of Tokicko, Nissin, and Brembos but never come across this "float" on any other application. What purpose does the "float" serve? Any negatives to removing it from the m/c? Thanks for any info...

 

Photo?

 

So you can see the level of the fluid in the sight glass easier....
and taking it out will not hurt anything..... but remember you heard it from some guy on the internet....

 

Also, it keeps the fluid from creating bubbles when moved in and out of the reservoar... So it has some useful value... I'd leave it there... Most other res have a rubber bladder that does the exact same thing, instead of the foam thing...

 

Ok Mike. You suggest it's an aid for viewing fluid level in a "windowed" reservoir. I don't have this "float" in the reservoirs on my '94 CB1000f, '97 Bandit, '99 ZRX 1100, '02 FZ-1, '06 Speed Triple with Rizoma reservoir, or '07 Bimota DB6 Delirio- all equipped with metal,"windowed" reservoirs. I'm not sure about the rubber part that Tweety suggests are located in other reservoirs either. The only visible rubber part I ever see is the diaphragm.

 

That's just an accordion-like rubber piece that goes up and down with fluid level. That's all it does.

 

Can't say for sure on the Bimota and the CB, but the others should if completely stock have the rubber bladder... At least according to the manuals...

 

The rubber "bladder" you guys refer to has a specific purpose - to seal out the environment from the fluid system while still allowing expansion of the system. As the brake pads wear out, more fluid moves to the caliper area since the pistons are more extended. This moves fluid out of the reservoir and lowers the level. The bladder is shaped the way it is so that it can expand into the reservoir. If you look closely, you will find a very small hole in the reservoir cap somewhere that allows air on top of the bladder so there's no negative pressure created when the bladder moves down.

As for the floaty piece in the reservoir, lots of cars have them, but I think those are specifically linked to low level warning sensors. I think for bikes, part of its purpose is to prevent bubbles from forming in the fluid. Part of it may be to aid in detecting the level. Probably more the former than the latter.