899 Dark Brake Fluids

Quite normal for the clutch fluid to discolour in a relatively short space of time. If you consider how much use the clutch master cylinder gets used, not really surprising. Doesn’t seem to affect performance unless extremely black but a simple process just to flush new fluid through if you want to see golden fluid instead of murky fluid. Andy

 

This question has been asked by Ducati owners for over 25 years. There has been no definitive answer to the cause, but we have found that some brake fluids that do not discolor when used with some aftermarket slave cylinders.

The color change has no effect on the clutch function and can be ignored, but inquiring minds simply can’t let go of this topic.

The clutch hydraulic fluid is heated by the engine at the slave unit, and hot hydraulic fluid will chemically attack some seal materials more rapidly than others. We don't know what aftermarket slave cylinders use what seal material, and we don't know what brands of hydraulic fluids have better material compatibility with the slave unit seals. Some slave units have hard anodized bores that are smoother than the OEM bore — which may also be a contributing factor to the seal erosion.

The rear brake slave unit and/or reservoir also sees continuous heat from the exhaust pipes on some models, so hot fluid is again a contributor to the color change.

We do know that there are numerous owner’s reports that say changing from the OEM slave to an aftermarket slave has resulted in the fluid remaining clear. However, this is not the complete answer because when the owners changed their slave unit they also replace one hydraulic fluid with a different hydraulic fluid. Some reports identify the fluid(s) used, some don’t.

For example, I replaced a Ducati 916 slave with an aftermarket Evoluzione unit, and flushed the system with Valvoline SynPower Dot 3/4 fluid — the fluid remained clear for over two years (yes, I know it should have been changed at 18 months).

You will also find owners reports stating that using BRAND X fluid stopped the color change, but the reports often don’t identify the manufacturer of the slave unit being used. Perhaps another owner has discovered a fluid that’s compatible with Ducati slave units. There’s at least four reports that ATE Super Blue doesn’t darken in a bike with an OEM slave cylinder.

So, without complete owner reports we don’t know what combinations of fluid and slave solve the problem.

Note that mineral oil is now specified for use in Multistradas and owners report that it doesn’t turn black when used with Ducati slave cylinders.