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MG MGB Technical - black fluid in clutch master

Hello everyone. Forgot to wish you all Happy New Year!!

My clutch fluid is black. Even after bleeding it becoming black again in a short few days. There is no issue using the clutch, but I know this is a warning. I replaced the MC and Slave at the same time with new Girling parts from Moss about 5 years ago ( say 35K miles). I do bleed it every 6 months to a year to keep it clear.

I was just going to rebuild the slave although I read that the slave would leak first and I do not see any leaking. Do you have any ideas?

Much appreciated!
Max71

Know this is a dumb question, but what brake fluid are you using? Sounds like something is reacting with the rubber in the cylinder or the brake line.
Bruce Cunha

You know I was thinking the same thing. I always used Castrol Dot 3 LMA. Then they stopped making it so I went to Castrol Dot 4 which I researched and the reports from racers said it was the same thing.

Oddly the brake master shows clean fluid with the same.

When I replaced the clutch master & slave I also replaced the copper line and rubber line (got a steel braided one). So its a whole new sytem as of 5 years ago.

However, you're right that something is eating rubber I just wonder which rubber so I can replace it before I get stuck. I use the car as a driver so that would suck when its telling me something.
Max71

Max, sounds just like a deteriorating rubber problem to me too. There are a great many poor rubber products about. Could be Moss are importing some dubious units. Check with them, it's unlikely to be the fluid!
Allan Reeling

Does sound like rubber. When I replaced my hose and slave I flushed the old fluid out first and that came out black to start with, however it was still clean in the master. Could be the master seals deteriorating, or just gunge lying in the bottom of the master that can't be flushed out as there is still about 1/2" or so of fluid left if you drain it by pumping.

DOT4 is compatible with LMA, but DOT5 isn't as that is silicone. Amazingly an improved version of DOT4 was produced - and called DOT5.1! To avoid confusion it's often labelled 'Super DOT4' here in the UK and is probably as good as LMA was, although DOT5 is less commonly available now at main-stream suppliers as it's not compatible with ABS.

"got a steel braided one"

Bad idea. I know of someone who did that, and when their engine earth strap failed it blew the hose, stranding them.
paulh4

Thanks all! Agreed it must be rubber but I'm trying to figure out which rubber. I was hoping the slave since its the easiest.

I guess there is a couple options which make this more intensive.

1. Flush the system with 99% isopropl as I've read people do this before putting in something like DOT 5 and see if that gets rid of the grunge.

2. Replace the seals in the slave and the master (ugh).

3. Replace the braided hose.

4. All of the above.

Yeow on the steel braided cable. The story was it wouldn't expand as much when using hydraulics and I thought the pedal felt better. I'm very careful with the ground strap but that would really suck.
Max71

The usual Goodridge type braided flexibles are not rubber and therefore unable to be the cause of your "black grunge" problem. As for them becoming primary earth straps, just make sure you have a good earth strap in place and don't worry! As for seals, make sure you get good quality items, but where from in the States i wouldn't know.
Allan Reeling

Then I'll rebuild the MC and slave which should take of it. My only options are BPNW or Moss so flip of a coin I guess.

Thanks for the help!
Max71

This thread was discussed on 22/01/2017

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