Clutch Fluid Burnt/black after 2,000 miles
 

I flushed/bleed the brakes and clutch system with some new bottle, cheap DOT3 fluid back in April or May. Since then the car has about 2,000 miles on it, and 3 nights at the drag strip, about 25 passes total. In 2,000 miles, the brake fluid is still as clear as the day I poured it in. The clutch fluid is dark and nasty looking. Clutch slave/master were replaced in 2013, and have maybe 6000 miles on them. The clutch system probably has water in it, as after making 6-7 passes at the drag strip, I start missing gears as the clutch isn't fully disengaging when I stab the pedal. This has happened before and new fluid always fixes it, but it's a short lived fix before it happens again.

Why would the clutch fluid have such a short life? I bought some DOT4 fluid today and I'm going to flush it and fill with that, but I was curious WHY this is happening and how I can fix it. I searched and didn't find anything, feel free to point me to the thread if this has already been covered/solved.

bad slave or bad master, or both. I'm going to guess slave... although last time this happened to me it was a bad master but I replaced both anyway.

It's rubber o-ring material turning the fluid black, the line is ran free and clear of heat so I doubt it's being burned.

I sucked my reservoir dry as I was bleeding my brakes a week or two ago, the refilled it with clear fluid. It's already going black again, and my master and slave are less than a year old, stainless clutch line.

The clutch goes through a lot larger range of motion, more often than the brakes and with less fluid capacity. I'm guessing my $14 master and slave are just a yearly maintenance item at this point.

Rubber O-ring turning it black seems very plausible. But why? Just a crappy O-ring? Or got too hot? I really want to find the cause of the problem and fix it. Bleeding the clutch system ever 3 months is not my idea of a solution.

I have my old slave and master, I was going to see about polishing the bores and potentially sourcing a better quality o-ring, seal or whatever somewhere other than the $14 atuozone kit. I just bought rebuilt units instead of the rebuild kits last time.

The clutch fluid can't get that hot, it'd be interesting to check it when the clutch goes soft.

I have new (not rebuilt) slave and master on my car. Mazda parts.

What would you check when it goes soft? I'm going to flush the fluid in a few minutes, and going to the track tomorrow. I can check whatever is needed before/during/after running it on the track to see if anything changes.

Just thought of this. So I have an ACT Extreme clutch, about the stiffest pressure plate you can buy for a miata. So I suppose my Slave is seeing a lot higher load than it would stock since pedal effort is much higher.

You might be on to something, perhaps the bore isn't smooth enough and the high load is smashing the rubber O-ring against the bore and rubbing it away. This is assuming the bore isn't that smooth, but I don't know how mazda finishes them.

Interesting though, maybe I'll pull it apart this weekend and see what it looks like. That could be the problem.

I'd just check the fluid temp in the reservoir, see if it is exceptionally hot or anything. It does get cycled a lot and compression will heat it, moreso with heavier parts, but I still can't see it getting soft because of the fluid boiling.

It moves a pretty decent volume on every stroke if you've ever seen a failed master bypassing straight to the resevour, so the temperature might stay kinda even throughout?

I'm interested to see what you find on the bores if you take them apart though, maybe someone needs to make stainless pistons for them or something, slightly larger diameter so the housings can be bored slightly.

I flushed it out. The old fluid literally looked like dirty black water. Thin and dark, with the consistency of water. Flushed the crap out of it, cleaned the reservoir, etc. It's got super clean DOT 4 in it now. We'll see how that holds up for now.

Could be the problem:facepalm:

I replaced the entire system at one time including the master, slave, and switched to a stainless steel line. The system was bled and new fluid provided by 949 was added. The fluid was black again within 3 weeks. I just run it like that because that is how it was before and I have no problems with it and it doesn't seem to have an effect on anything. I'll bleed and switch out the fluid on a regular interval unless I notice leaks or performance degradation.

Interesting. Looks like I'm not alone.

But in my case, it does affect the shifting. I can't get it to shift once the car gets really heatsoaked at the drag strip. New fluid is always the fix.

What fluid did you use? Also, what brand parts?

Try a high temp fluid instead of the cheapo stuff. Bottle of motul rbf600 is cheap and would tell you if it was getting too hot.

Where is that fluid bought cheap? Amazon shows 18.65 for 0.5 L bottle.

But you're right, if this DOT4 I used isn't the fix, I'm putting in unicorn tear brake fluid to see if that fixes it.

Hmmm thought it was cheaper.

Try ATE Type 200. Similar unicorn tear content but you get 1L for $20 $17 (keeps dropping) on amazon.

I am using whichever fluid is provided by 949 kits. I believe it was a motul fluid but I couldn't tell you what type anymore.

Emilio provides Motul RBF600 with the overhaul kit.

all miata fluid does this on the clutch. Doesnt matter, new or old parts, cheap fluid, super blue, rbf600. Has no effect on anything besides looks. Now your problem, guessing the springs popped out of the center of the clutch or the friction material blew apart or just a random unfortunate failure of your new clutch parts.

Miata clutch masters do that. No big deal. Change the fluid if it makes you feel better, but it will continue to work fine if you don't. I change mine once a year between racing seasons. I've seen some Miatas where the clutch fluid was completely black. It still worked.

Made 14 passes, fluid is as black now as it was yesterday before I flushed it.

Also shifting issue when hot is still present.