Nah that would be the mystery foam in the new and improved tool "kit" 
My truck has a float like that in the clutch master.
My truck has a float like that in the clutch master.
Is This a New ST Brake Part?
- Thread starter lenparkin
- Start date
Let me stir the pot some more 
any of you folks notice that it appears that only the Civilian bikes that have the "floats"? None of the ST1300AP bikes are shown to have them on the microfish. The 2011-neither master cylinder have them, 2010, 2009, zip, nada, nothing. I still believe the factory assembly person who's job it was to remove them and fill the m/c up with fluid before shipping them out.
I'm hanging onto my box of them until demand goes up and I get top dollar for them
any of you folks notice that it appears that only the Civilian bikes that have the "floats"? None of the ST1300AP bikes are shown to have them on the microfish. The 2011-neither master cylinder have them, 2010, 2009, zip, nada, nothing. I still believe the factory assembly person who's job it was to remove them and fill the m/c up with fluid before shipping them out. I'm hanging onto my box of them until demand goes up and I get top dollar for them
If that were the case they would not be in the parts list would they??
I think you're microfishing there...
nah, but sometimes avoiding work is more work than work LOL
I wonder......could the mystery part be used to keep the diaphram from being sucked down into the master cylinder? I'm always finding folks diaphrams in that condition. Perhaps the foam floating on the surface of the fluid would provide a flat surface against the rubber and hold it in place? Just wondering now....
Blrfl
Natural Rider Enhancement
That's not how it works. When you squeeze the brake or clutch lever, the master cylinder pulls fluid out of the reservoir and is used to expand the system's volume enough to push out the pistons in the brake caliper or slave cylinder. If the system were completely sealed and inelastic (like a glass jar), sucking fluid out of the reservoir would require pulling a vacuum on the air in the reservoir. That would consume some of the energy you're applying to the lever that would be better spent doing braking. The diaphragm is flexible so that when the system pulls in fluid, it pulls in along with it, keeping the amount of air in the reservoir constant. (Ideally, you want no air at all, but that's not practical.) When fluid is returned, the diaphragm relaxes.
If you look carefully at the left edge of a master cylinder cover, you'll find a very small notch which allows the top side of the diaphragm to inhale or exhale outside air as fluid is pulled out of or returned to the reservoir. This prevents having to pull a vacuum, because as the diaphragm is pulled into the reservoir, there's outside air available to fill the void without any extra effort. Because the diaphragm acts as a barrier to the outside air, you don't have a constant source of new moisture. Finding diaphragms pushed into the reservoir is a good thing. That means it's doing its job.
The float is there to do two things. First is to minimize the amount of brake fluid exposed to the air in the reservoir. Without it, 100% of the surface has a chance to mingle with the air; with it, it's only a small fraction. This cuts the rate at which the fluid sops up moisture by just as much. Second (and this is conjecture) is to keep moisture that's accumulated on the diaphragm from dropping back into the brake fluid or being washed back into it as the fluid sloshes around. The diaphragm on my '04 is almost always wet when I remove it, and I'd bet dollars to doughnuts that the top surface of the float comes out wet on newer bikes. All of that extra moisture is being kept out of the brake fluid.
--Mark
Overfill it past the fill mark and fluid will leak out.
I just love a good mystery....here's my thoughts tonight.
RonAyers.com
06, 07, 08, 09, 10, and 11 don't have them in the Clutch Master cylinder.
06, 07, don't have them in the brake master cylinder, however, 08, 09, 10, and 11 show the "float" on the civilian models ONLY.
Anyone notice that on the 08 or 09's and newer models that the front brake lever and master cylinder assembly is the same one as on the wing?
The body is larger, and the lever has relocated the plunger and concealed it, and added another number on the wheel.
Perhaps the reason they only specify the "floats" from 08 on is because of the larger unit. Maybe with the extra room in the housing, they need it to take up space?
But again, if it were important, why would they leave it out on all of the ST1300AP Police models?
Tonight I opened both my M/C's up, made sure the fluid was level and at the correct line, then inserted one in each M/C then put the lid back on....you know what happened?
It forced fluid out the edges because the extra thickness took up space at the correct fill line.
I'll have a 2012 in the garage for a service job on Sunday, I'll check the housing, level line, and look for differences between the models more closely then.
I took the floats back out of mine, and the level remained at the level mark, and it didn't force any fluid out, so I'm guessing it may only be needed, if at all, in the later models that have the Goldwing M/C housing and lever.
Anyone care to debate?
.02
RonAyers.com
06, 07, 08, 09, 10, and 11 don't have them in the Clutch Master cylinder.
06, 07, don't have them in the brake master cylinder, however, 08, 09, 10, and 11 show the "float" on the civilian models ONLY.
Anyone notice that on the 08 or 09's and newer models that the front brake lever and master cylinder assembly is the same one as on the wing?
The body is larger, and the lever has relocated the plunger and concealed it, and added another number on the wheel.
Perhaps the reason they only specify the "floats" from 08 on is because of the larger unit. Maybe with the extra room in the housing, they need it to take up space?
But again, if it were important, why would they leave it out on all of the ST1300AP Police models?
Tonight I opened both my M/C's up, made sure the fluid was level and at the correct line, then inserted one in each M/C then put the lid back on....you know what happened?
It forced fluid out the edges because the extra thickness took up space at the correct fill line.
I'll have a 2012 in the garage for a service job on Sunday, I'll check the housing, level line, and look for differences between the models more closely then.
I took the floats back out of mine, and the level remained at the level mark, and it didn't force any fluid out, so I'm guessing it may only be needed, if at all, in the later models that have the Goldwing M/C housing and lever.
Anyone care to debate?
.02
I checked for 2007, and the diagram is the same as the one Mellow linked to. However, in the parts list for the '07, there isn't a part #25 shown (even though the diagram shows it); it only goes to #23. Something changed in '08.
Yet more fuel, that someone, somewhere, just messed up the microphish? And why no P models?
The Urban legend continues
I'd really like to find out what its for now....OCD its a beautiful thing
I would assume if it was overfilled, the diaphragm would push fluid out as you buttoned up the reservoir.
I think this idea has much merit. Mainly because I mentioned the same thing to someone saying maybe it's to prevent cavitation. (Hyperbole)
Hm. That would seem to displace most if not all air, in a slightly inelegant manner.
Depends on how full you fill it... if you fill it to the very top level then yes, but is you just fill a little past the fill mark - maybe half way between the fill mark and the top of the reservoir, then the extra fluid is pushed out of the very small holes Blrfl spoke of... that happened to me when I first did my brake fluild on one of my wings.
OP
OP
The float was only in the front M/C, not the rear or clutch M/C, on my '10 ST. The service manager at Scott Powersports said the float was added in '08. He didn't off a reason why.
Len
I have an 06 w/o ABS and it was present in both master cylinders - clutch and brake. It tastes like packing foam
Blrfl
Natural Rider Enhancement
The police model is based on the '05, which had the older part. There may be stock-on-hand reasons for using it, as earlier STs were produced in much larger quantities than later ones. It could also be that one of their larger customers had a bolt-on farkle that wasn't compatible with the GL assembly.
At any rate, I doubt that this change is somebody's-gonna-faceplant-on-the-road-without-it important.
According to the fiche, that shouldn't be there. Even on '08s and later, the clutch reservoir doesn't have a float.I have an 06 w/o ABS and it was present in both master cylinders - clutch and brake. It tastes like packing foam
--Mark