Ever since I bought my car, the clutch fluid has had a blackish tint to it. Since, I have replaced the master and slave cylinders, and the clutch line. I put in Valvoline DOT 3 & 4 brake fluid, and it is still turning black! What gives?

 

Result of normal wear. The black rubber seals on the MC and slave plungers wear against the cylinder bores, leaving microscopic particles suspended in the fluid. The quality of rubber used in cheaper aftermarket components often wear faster.

 

N e e d m o r e i n f o . . .

The hard line, or just the rubber line to the slave? Did you replace all these items at the same time, or different phases?

At different times? Both new? Used?

A full system flush should do the trick, and just use ONE brake fluid. Brake fluid also has a relatively short life (1-3 years). And the more times you open up the cap to "check" the level, the more moisture you allow into the system.

 

1/31/15 - Replaced the rubber line to the SC with a stainless steel line.
3/25/15 - Replaced the SC
3/26/15 - Replaced the MC


The brake fluid came from the same bottle. I flushed the entire system each time one of the components was replaced.

I actually started changing the MC and SC because the clutch was disengaging far too early out of nowhere. I just figured the clutch fluid would be clear with all new components.

 

I would figure after some time, but not after a week or two... something seems suspect.

 

I always wonder about upgrading to the latest and greatest fluids on a car designed more than 30 years ago. I looked up the product specification for the Valvoline DOT 3 & 4 fluid you used. Nothing suspicious about compatibility with a broad range of rubber formulations. I downloaded the MSDS sheet and something caught my eye on page 7 (see attachment). This fluid is listed as incompatible with aluminum components. I just purchased an aftermarket clutch master cylinder for my Z31, and I recall it has an aluminum body. I think the in-line modulator is also made out of aluminum. I haven't looked at the slave, yet. Corroded aluminum would certainly turn the fluid dark. The product guide only mentions use in brake systems and perhaps Ashland assumes all components are made from ductile iron. Like I said, this is only a guess.

FYI, the Pyroil Brand DOT 3 fluid manufactured by Ashland Oil does not list aluminum as incompatible in that MSDS.

 

Wow, Ken, that is great information. Yes, the MC and SC are cast aluminum. I always try to stay away from modern synthetics, but no local store seems to carry non-synthetic.

I use the same fluid for my braking system, and this blackish hue does not occur, which makes it even more of a mystery to me.

Maybe I will try out this Pyroil DOT3 that is compatible with aluminum just to see what happens.

 

You can always use Super Tech DOT 3 from Walmart. People scoff at using this brand, but all the Super Tech automotive fluids are tested and approved to industry standards.

 

Clutch hydraulics move a lot more volume of fluid per line than the brake system does. The caliper pistons only move a fraction before pressure builds and braking action occurs. Also, the calipers are made of cast iron, the pistons are chromed or polished steel. Again I am guessing, but the brake system has less exposure to aluminum and less fluid mixing so this phenomenon would take longer to manifest itself.