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Old Sep 5th 2018, 04:22 AM   #11
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Do not remove the rubber boot inside the reservoir. This rubber boot serves as a "regulator" of sorts to keep vacuum and pressure in the system. If you have a leak in the slave cylinder or master (like a lot of us have had) this rubber boot expands in order to maintain vacuum & pressure. Without the boot in place you will most certainly pull air into the reservoir when releasing the clutch lever. This will then act like a siphon and all your fluid will just DRAIN out. This rubber boot is very very important to the proper operation of the system.

With that being said,... Like Halo2 stated above,... in almost all instances these leaks are caused by either the slave cylinder or master cylinder. Or if someone has previously screwed with the system and improperly torqued a fluid line.

Honestly, proper care of your bike (monitoring fluid levels to be sure clutch reservoir doesn't go empty) and proper maintenance are key. All bikes have problems of some sort. Just so happens ours has problems with the clutch slave cylinder (and a few others). Buy a CNC racing slave cylinder and sleep peacefully.
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Old Sep 5th 2018, 05:39 AM   #12
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Originally Posted by kensteele View Post
but we know changing hydraulic fluid and changing slave cylinder seems to work in some instances. is there ever a case changing to a larger reservoir has solved the problem?
It may simply be an issue of fluid level. As the fluid volume decreases, the likelihood of the air void reaching the reservoir drain increases. There is a certain set of criteria where it MAY happen, low fluid in reservoir, high lean or deceleration which moves fluid AND actuation of clutch. If you don’t use the clutch it won’t be an issue.

Reservoir size is determined by the amount of fluid that is required to account for wear. If you fill the reservoir to the max when new, it may be enough volume to prevent the fluid level from dropping to a point where the reservoir drain is exposed to the air. As the clutch wears the fluid displacement is larger which MAY lead to the reservoir drain being exposed. If you actuate the clutch lever at this point you would draw a small amount of air in to the system. Over time this air would grow, leading to a spongey clutch. As I said before this is due mainly to the mounting orientation of the reservoir. Mine, stock sits angled forward about 40 degrees so when you have the cap off and your reservoir is near the minimum mark the drain is very nearly exposed. I actually had to twist it in order to fill it properly so I wouldn’t introduce air while bleeding when the fluid levels were above the min line. What I did with mine was to bend the bracket so the reservoir was as close to horizontal as possible. I then filled it to the max and will watch it.

If you consider the “cures” I’m not sure. Changing the fluid may simply have fixed the issue by raising the fluid level. But in terms of heat, the transfer to the clutch slave cylinder is much lower than the boiling point of standard brake fluid. So I would be very skeptical that boiling is the issue. Is it a bad master or slave cylinder? Always a possibility, but Brembo has been doing hydraulic systems at the highest level for pretty much ever. I’d bet their seals and tolerances (even at the OEM level) have been pretty much sorted out by now.

Anyway, it is just something I observed and shared as a potential source of a problem. Up to you to decide if it does or doesn’t contribute. Adding a larger fluid reservoir will decrease the amount the fluid level changes in the reservoir. It will cost you $20 or so to fit a slightly larger one. Or you can bend the bracket and keep the reservoir close to full for no cost. IMHO that is a good first step to resolving the issue.
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Old Sep 5th 2018, 03:18 PM   #13
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What I found with mine or at least I think I found. My rubber boot was completely expanded when I went to fill it, I had no idea that it got depressed (squeezed together). For some reason with it completely expanded it would suck air into the reservoir. Once I properly folded it up and made a good tight seal, plus re-bleed then it started working right. Before I did this I'd bleed the system, drive like 10 miles and already the clutch would be impossible to get into neutral and was very hard to shift (with the clutch), plus you could feel the sponginess in the lever. I hope all is good now. I drove over 30 miles this morning and never had an issue with it.

I know you that JARHEAD said that the rubber boot acts as vacuum to keep pressure and it can expand if there is a leak in the slave or Master. I hope I don't have one, but would be covered under warranty, but I hate being without my bike.

I did remove the rubber grommet just to see: Yes, I did suck air and fluid leaked at speeds.

Thanks for all the comments, appreciate it.
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Old Sep 5th 2018, 03:26 PM   #14
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[QUOTE=As far as the air, I just had to bleed mine and was wondering how it got air in the line. .[/QUOTE]

If your rubber grommet was expanded then that would explain how air got into your system. I know when mine was expanded it sucked air.
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