Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 998 / 996 / 916 / 748 > black clutch fluid

[Mello-Yellow]

Noticed the clucth fluid in the reservour has turned black literally over night,It was changed at the last service 4 weeks ago
.

Heard it might be the seal on the cylinder weeping but i dosn't seem to be loosing any fluid.

Any Ideas

[Ian 748]

chain crud drawn through the seal by the push rod i was told.

[Shazaam!]

I've been following this topic with interest for a few years now and I've collected a lot of anecdotal information about this phenomena from discussions on the web. Here's a summary of reported observations and my own experience:

(1) The clutch fluid darkens on new bikes before leaving the showroom.

(2) Replacing the clutch hydraulic line has stopped the color change.

(3) Replacing the clutch slave cylinder has stopped the color change.

(4) Replacing the clutch master cylinder has stopped the color change.

(5) Honda claims their new clutch fluid will minimize fluid darkening on their bikes.

(6) The clutch, but not the brake hydraulic fluid changes color.


Speculation on the source of the contamination includes:

(1) Particles shed from the rubber hydraulic line material.

(2) Particles worn from the slave cylinder seal material.

(3) Aluminum particles worn from the OEM slave cylinder bore material.

(4) Contamination of the fluid by debris flung from the chain.

One observation has been that if you change to one of the aftermarket slave cylinders that have a different seal material that either has no carbon black or is more abrasion resistant, then the fluid color shift stops, or at least slows significantly. Since these aftermarket units have a hard-anodized finish on the bore, it's been suggested this also helps to reduce seal abrasion and particle release. The aluminum stock unit piston bore isn't hardened, so it's been assumed that minute aluminum particles also contribute to the darkened color.

I believe that this is a red herring. In all cases, the common factor in minimizing or eliminating this problem has been to replace the Ducati OEM brake fluid that is installed at the factory. Whatever fluid (extra-virgin olive oil?) they're using, it darkens from some combination of moisture, heat and age, or more likely by just by chemically attacking the rubber lines and piston seals that releases their carbon black into the fluid. (Remember, when you change out a component you also end up changing a good portion of the fluid.)

I suspect that continuous heat plays a part in breaking down the synthetic rubber slave seal and hydraulic line material, since the slave cylinder (and adjacent line) is mounted directly to the engine casing. Brake hydraulic fluid that sees intermittent higher temperatures does not undergo this discoloration. However it's possible that Ducati uses a different fluid for the clutch and brakes.

One clue is that Honda claims that their new improved clutch fluid is formulated to minimize the same color change in Hondas, suggesting that Honda has found that the problem is somehow accelerated by the hot hydraulic fluid chemically attacking certain materials rather than by seal wear alone. So they reformulated their fluid or perhaps changed vendors.

Another clue is that black hydraulic fluid has also been observed in cars. A chemical analysis by Detroit gurus determined that the color came from carbon black suspended in the fluid. It was leached out of piston seal material or the hydraulic line and into the fluid, turning it black.

Reliable reports from Ducati owners say that if you replace the clutch slave unit and/or the stock hydraulic line with aftermarket units the color change stops. This is not the real solution to this problem however. The common thread is that owners flush the fluid when they change these components. Several owners reported that the color change stopped after simply changing the fluid.

The bottom line is - ignore it. It doesn't hurt anything. If you can't live with black fluid, flush out the factory fluid. Change it every 18 months or so to remove moisture buildup (absorbed from the air) that will corrode any metal that it comes in contact with.