Why does clutch fluid turn black so soon. - Ducati.ms - The Ultimate Ducati Forum
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post #1 of 38 (permalink) Old Jul 2nd, 2009, 1:07 pm Thread Starter
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Why does clutch fluid turn black so soon.

Why? And what is that black crud that settles in the bottom of the clutch fluid reservoir? The brakes don't do it and you would think that would suffer the worst duty. ???

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post #2 of 38 (permalink) Old Jul 3rd, 2009, 11:40 am
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The fluid is in a closed loop. It should not produce any crud. Maybe try completely flushing out the line with new fluid and wiping out the reservoir. Also, check to make sure your slave cylinder does not have any leaks or bad seals which is pretty common. Good luck!
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post #3 of 38 (permalink) Old Jul 3rd, 2009, 11:46 am
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Bump, Someone please explain this for me also.

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post #4 of 38 (permalink) Old Jul 3rd, 2009, 11:57 am
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I believe it's a reaction to moisture. Hydraulic fluid absorbs moisture. It may be from condensation inside the system, or moist air seeping in from outside the system. It happens quite a lot up here in Canada with our big temperature fluctuations. Just flush your system once a year and it will be fine.
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post #5 of 38 (permalink) Old Jul 4th, 2009, 10:18 am Thread Starter
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But why only the clutch and not the brake. All my bikes do it and I've noticed it on other's bikes also.

Mike
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post #6 of 38 (permalink) Old Jul 4th, 2009, 3:21 pm
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It's caused by aluminium particles dissolving into the clutch fluid, probably from the unfinished aluminium bore of the crap standard slave cylinder. Most aftermarket slave cylinders have anodised bores, or are made from a better grade of aluminium, so you'll notice that bikes with aftermarket slaves don't suffer from the problem.

BTW, it doesn't adversely affect the operation of the clutch, just looks bad.
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post #7 of 38 (permalink) Old Jul 4th, 2009, 4:33 pm Thread Starter
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Quote:
Originally Posted by rob998 View Post
It's caused by aluminium particles dissolving into the clutch fluid, probably from the unfinished aluminium bore of the crap standard slave cylinder. Most aftermarket slave cylinders have anodised bores, or are made from a better grade of aluminium, so you'll notice that bikes with aftermarket slaves don't suffer from the problem.

BTW, it doesn't adversely affect the operation of the clutch, just looks bad.
Thanks. Sounds logical. Your right, it's never been a problem, just looks nasty.
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post #8 of 38 (permalink) Old Jul 9th, 2009, 12:31 pm
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Here's why. None of your reasonings make sense because as Duckman stated, why the clutch and not the brake?? Same components, same materials, same design. Except...

Unlike the brake system, as the disc in the clutch wear, (and along with the natural flow of fluid in the system) fluid is displaced into the reservoir. In a brake system, as brake pads wear and the piston is displaced further into the caliper, the fluid in the reservior decreases. With the clutch, the fluid in the reservior increases, bringing along with it, any contaminants, crud, or dust that happens to get into the system. If you'll notice, this is why you have a 'min' and a 'max' line on the clutch reservoir, but only a 'min' line on the brake.

We could argue how that gets into the system yes, but this is the reason it gets into the reservoir. If look closely however (at least best I have noticed on all three of my Ducs) the crud ends up in the reservoir stuck to the sides or resting in the bottom and not suspended in the fluid. I have never seen any detrimental effects from this, but I personally have never owned a Ducati that didn't do it.
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post #9 of 38 (permalink) Old Jul 10th, 2009, 1:23 am
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Actually the black stuff is the sealing ring in the slave that deteriorates and gets into the fluid. I took apart a slave and found the black ring to leave black crud on my fingers.
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post #10 of 38 (permalink) Old Jul 11th, 2009, 9:29 pm
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The crud is as previously stated aluminum and rubber. The fluid darkens as it ages because it is hydroscopic and the water it picks up contributes to the corrosion of the cyl. bore.The reason it turns color so quickly is the relative distance the seals travel is about 4 times greater than in a brake cylinder.And the loading on the seal increases as it slides down the bore unlike the brake which stops moving pretty much at peak pressure.Just change the fluid once or twice a year if it gets too dirty.
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