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Discussion Starter · #1 ·
Several months ago I had some issues with air getting into my clutch system. Had to bleed it every week or two. Tried putting some thread tape on the bleed nipple, which fixed it.

Then recently, my bike started to use clutch fluid, and get a little air in the system as well. Could not see any fluid around the clutch lines or bleed nipples, after topping up the reservoir 2-3 times over the space of 3-4 weeks I saw the fluid was leaking from inside the slave cylinder and dripping on the chain/exhaust.

Not wanting to go anywhere near the local dealer again for warranty work (last time I took it there for warranty they had it for 6 weeks over a simple gasket replacement), I stripped it down myself.





The fault was the seal was leaking. The seal on the system is a basic, dodgy single lip seal that only seals properly when under pressure. Additionally, it appeared to have been either poorly manufactured or damaged by the brake fluid I was using. As well as that, the cylinder bore was not as well honed as you might expect, and was exhibiting far more wear than you might expect from a bike with only 6000km on the clock. Its a little hard to see from the photos, but its the best I can do.

Also, the seal is an odd size, and you cannot buy an off the shelf part for it - to replace it you have to try and go though a Brembo dealer. I have the Brembo part number off it and will post it up later, however google searching on it shows it has been used on a variety of bikes over the years and is not unique to the 899/1199.

Basically, this clutch slave is garbage and not the kind of quality you would expect to see on something with a Brembo brand name. Even using a single lip seal screams 'cheap' to me, IMO. I have ordered a replacement Oberon slave to replace it but I'm not happy it has been necessary to do this as a repair after so few KM. A simple google search shows this is not an isolated problem either.

Lastly, I have heard *note: I don't know how true it is* that the seals on these slaves are so crap they cannot cope with modern brake fluid additives, and if you use anything better than the recommended fluid they will eventually leak and fail. Even if you are still using DOT 4. Don't know if that's got any factual basis or not, but it seems feasible... I don't know what material they are made from though.
 

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Wow, that's interesting.

About the cylinder bore--I put about 100 miles on my custom V8 Miata and realized the aftermarket Brembo master cylinder was leaking.... inside the car. I took it out and disassembled it like you did and the bore was UNBELIEVABLY scored. I made sure to line everything up when installing. I tossed it and replaced it with a Tilton, no issues so far...

I'm wondering what's going on with Brembo as a company, I've heard so many complaints lately! My buddy with an 1199 has constant issues with his clutch, also. We will be doing the teflon tape 'fix' soon.

I haven't had any issues with my 899 and I have almost 40,000 miles on it.

My reservoirs eat the seals, that's about it. They just get pulled/sucked down inside the reservoir. No clue why. I haven't noticed it happen on any other bikes.
 

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Wow, that's interesting.

About the cylinder bore--I put about 100 miles on my custom V8 Miata and realized the aftermarket Brembo master cylinder was leaking.... inside the car. I took it out and disassembled it like you did and the bore was UNBELIEVABLY scored. I made sure to line everything up when installing. I tossed it and replaced it with a Tilton, no issues so far...

I'm wondering what's going on with Brembo as a company, I've heard so many complaints lately! My buddy with an 1199 has constant issues with his clutch, also. We will be doing the teflon tape 'fix' soon.

I haven't had any issues with my 899 and I have almost 40,000 miles on it.

My reservoirs eat the seals, that's about it. They just get pulled/sucked down inside the reservoir. No clue why. I haven't noticed it happen on any other bikes.
I had read somewhere this function is to help prevent excess air from entering the system from the reservoir. Of course, it would have been better to have a master cylinder that didn't leak as well. ;)
 

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That sucks alright.
Even thou its brembo, it still "cheap, mass produced" brembo. But im still surprised.
Be interesting about the seal material reacting, unless there is a higher silicon content in brake fluid....

Maybe hsould just either use ATF or go cable converstion :)
 

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You need to be careful replacing the rubber seals.

Most people think Viton rubber (expensive sh#t) is the best but it ISN'T.
Not for brake fluid. Brake fluid eats Viton. Our o-ring suppliers recommend EPDM
rubber.

I've seen it degrade too. Drop a piece of Viton into some brake fluid and it swells, goes soft and breaks down.

And that rubber seal you pulled out looks like crap. I could probably make a better one here at work. Just need a sample.
 

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Discussion Starter · #7 ·
Got a little more info for anyone looking in the future.

The seal is marked with brembo and a part number of 05426399. It also has an 18 marked on it.

The piston measures OD 25.85mm, seal groove diameter 18.20mm, groove width 4.36mm.
Bore diameter 26.00mm. All measured with verniers by a fitter and turner.

Brake fluid used was castrol react performance dot 4, which on the face of it should not have caused any problems. I have been using the same in the brakes and clutch.
 

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Discussion Starter · #8 ·
Sqweegel if you like i can post you the old seal. I have no need for a replacement anymore, but if you can make them and have any use for this one well its only going in the bin otherwise
 

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You need to be careful replacing the rubber seals.

Most people think Viton rubber (expensive sh#t) is the best but it ISN'T.
Not for brake fluid. Brake fluid eats Viton. Our o-ring suppliers recommend EPDM
rubber.

I've seen it degrade too. Drop a piece of Viton into some brake fluid and it swells, goes soft and breaks down.

And that rubber seal you pulled out looks like crap. I could probably make a better one here at work. Just need a sample.
Any concerns with brake/clutch fluid and the teflon tape?
 

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Any concerns with brake/clutch fluid and the teflon tape?
Teflon (the chemical PTFE - polytetrafluroethylene ) IS the
Best of the best. Chemically resistant to just about everything and can
Handle a wide range of temps up to 250 C. The problem is how are you going to fit it to the slave cylinder? I can't say if just wrapping it around the piston and rubber seal would work? Just comes down to trial and error on that one.
 

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Teflon (the chemical PTFE - polytetrafluroethylene ) IS the
Best of the best. Chemically resistant to just about everything and can
Handle a wide range of temps up to 250 C. The problem is how are you going to fit it to the slave cylinder? I can't say if just wrapping it around the piston and rubber seal would work? Just comes down to trial and error on that one.
You sound like you've been in the gasket industry also. Great point on the ptfe.
 
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