quote Originally posted by olejoedad: Patrick, my chemical attack remarks are not in response to your comments.

Must be that troublemaker Ogre's then ... although I don't believe even he actually suggested anywhere that brake fluid "attacks" the aluminum cylinders and/or pistons.

[This message has been edited by Patrick (edited 03-17-2018).]

My comments are only to prevent any misconception that brake fluid in a closed system could cause corrosion of the metals in the system.
We all know what brake fluid can do to paint.

When you press the clutch, you push fluid out and down the clutch line something like 20", when you release the pedal, that fluid comes back into the master. If it is getting dirty in a matter of minutes, then it is either coming from the clutch master (superfine aluminum dust left over from machining the master), or the protective oil coating on the inside of the new line.

I would suspect the coating on the inside of the clutch line. You can disconnect it at both ends and spray some brake clean through it to remove any residue (but make sure you protect items from the brake fluid and brake clean spay that will come out the end, unless you want the paint removed from anything it sprays on). This is best done before the clutch line is installed in the car.

[This message has been edited by fieroguru (edited 03-17-2018).]

quote Originally posted by Blacktree: After installing an aluminum clutch master cylinder and stainless steel clutch hydraulic line, I noticed the clutch hydraulic fluid now turns grayish-black instead of brownish. I guess that's the difference between aluminum oxide and iron oxide. I installed the clutch master and hydraulic line about 10 years ago. The clutch still works fine. So I'm not gonna worry about it.

See, that’s good info. Like experience. Just wish I had that data before assuming I had deteriorating seals. Although, the slave was still original, so probably okay that got replaced.

I think the chemical attack vs mechanical wear is throwing off the debate about the theory. Bottom line, I think the theory is that the brake fluid is pulling residue off the aluminum that is already there, even if not immediately visible otherwise

[This message has been edited by USMUCL (edited 03-17-2018).]

Talked with Rodney today. It was a great collaborative discussion on what the likely cause for this is. He's a good dude to talk to.

No one had ever mentioned this to him before. That doesn't surprise me, since I doubt anyone has ever replaced the entire hydraulics at once like this, including 2 of the 3 parts being his.

He, too, believed I am likely seeing where the piston seals, as they move, rub off small particles on the aluminum surface, then turning the fluid grey/black. He said he has sold "thousands" of these with no failures, so it must be inconsequential to performance.

The pistons are steel. I would have been willing to take the guts of Rodney's slave/master and put them in the OEM iron units just to test the theory. Unfortunately, while the slave innards are compatible, he didn't know if the master innards would work in the OEM housing. And, I can find no rebuild kit online definitively for our OEM master cylinder. Anyone know of one?

Actually.
Brake Fluids DOT3 are of a Glycol Ether Base, H−(O−CH2−CH2)n−OH.
Brake Fluid WIKI
Aluminum is not recommended by DOW for storage.
DOW CHEMICALS

Also note that Glycol Ethers chemically react with Zinc and tin and galvanized metals.
It can cause a discoloration of the fluid as well as the metals.

Hope this helps.