Ducati Sporting Club UK > Model Specific - Discussion, Technical Problems and Help > 998 / 996 / 916 / 748 > Clutch Slave Oil Gone Black ???

[ShakMan]

Hello all,

Can someone tell me if this is normal .... I bleed the clutch slave oil system with some new Dot4 oil.

However, after a couple of days I noticed the oil had gone from light yellow to dark murky blackish colour? I am wondering if something is over-heating and burning the oil?

[Sticky]

Exactly the same with me. Oil black, bled the whole sytem, black again. While bleed ing I noticed though it's not the oil thats gone black but black particles in it. I have been reliably told that it's rubber and nothing to worry about. That'll do me.

[Nigel Booker]

The clutch fluid on mine turned black on the 10 mile ride home after the 12k service.

[sevenfourate]

Same here - mines fresh and is black as the ace of spades.Looks like pondwater.Still working anway......

Syer.

Sticky - whers the rubber coming from ?

[Totto]

Ditto , same here on my 998 !

[Sticky]

don,t know where rubber is from, presumably lining the pipes. But it's not a lot.

[Shazaam!]

There's a lot of anecdotal clues about this. Here's a summary of reported observations:

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

(2) The fluid in brake reservoirs having the same fluid does not darken.

(3) Honda and Kawasaki motorcycles exhibit the same phenomena.

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

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

(6) Black debris has been observed in BOTH the clutch and brake lines.

(7) Honda says their new clutch fluid will minimize any color change.

(8) The clutch, but not the brake, hydraulic fluid reservoir change color.


Here's some speculation on the cause(s):

Candidate: Particles shed from clutch hydraulic line material.

Candidate: Contamination of the fluid by debris flung from the chain.

Candidate: Particles worn from the slave cylinder seal material.

Candidate: Aluminum worn from the OEM slave cylinder bore material.

Candidate: Ducati OEM brake fluid chemically attacking lines and seals.

Candidate: Hydraulic fluid darkens from moisture and age.


It's interesting 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 the aftermarket units also have a hard-anodized finish on the bore, this also helps to reduce seal abrasion and particle release. The aluminum stock unit piston bore isn't hardened, so it may be that minute aluminum particles also contribute to the darkened color.

Heat is suspected in playing 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 and sees continuous engine heat.

Honda claims that their new clutch fluid is formulated to minimize this color change, suggesting that Honda has found that the problem is accelerated by the hot hydraulic fluid chemically attacking certain materials rather than by seal wear alone.

Black hydraulic fluid has also been observed in Corvettes. A chemical analysis by Detroit gurus determined that the color came from carbon black suspended in the fluid. It was probably leaching out of piston seal material or the hydraulic line.

The solution has been to ignore it. It doesn't seem to hurt anything. If you can't live with black fluid, you can either flush it regularly or replace the clutch slave unit and/or the hydraulic line with aftermarket units.

[ShakMan]

Shazaam ... you're the man!

[sevenfourate]

Thanks Shazaam. Informative, interesting and helpful as always.

Poster of the decade ????

Regards Syer.

[pguenet]

Funny you say that. It does it on my 996SPS which is bulk standard but it does not do it on my track 916 which had just about everything changed there!