discolored fluid in clutch mc

[c.garde]

Help,please

After a complete rebuild I experienced dirt in the fluid in the clutch mc.
Mc is brand new " girling " and it lasted a year before the fluid went dark .
Happy that this is not the brake mc I took everything apart . On inspection the bore did not show any signs of defect. Same goes for the seals. Fluid is std dot 4.
On replacement I went to great lengths to locate an orig. Girling kit . Whatever this i these days . The price was certainly not standard.
This lasted this " summer " before the contamination presented itself again.
Speaking the other day to a friend with an Esprit ( same mc ) he told me about the same problem.
He did also try to fit new seals to no avail and has now bought a replacement mc at Nec.
I would be grateful for feedback , Thank you.

Claus Garde

w, equial I could not see anything wrong with the b i noticed the darwa

[miked]

Claus, I may be wrong but I have had this and put it down to exhaust heat acting upon the slave cylinder rubber and degrading the rubber. I tend to find that running an Elan or Plus two that slave rubbers tend to degrade and swell and colour the fluid then start to drip. Usually about 3 years and I change the slave rubber. Maybe the heat also affects the fluid to encourage oxidisation and sludge. Others with more knowledge about fluids
may verify this. I can only talk from practical experience. Mike

[Quart Meg Miles]

Claus,
I take it you are LH drive (would be helpful to have your location and car in your posts. I happen to know your car is a Sprint). Heat may well be the problem, or oil vapour, though I don't recall any other reports.

I had a RH drive S130 which filled its master cylinder with 2 mm spherical crystals a while after refilling with new Girling fluid. One of them interfered with the piston and left me with no clutch and the Girling rep claimed he had never seen such a thing before. Clearly not heat but might have been water vapour as the car was not garaged.

[Grizzly]

As above...... I had the same issue, brand new Master,Slave and lines which started to play up in warm weather sat in traffic, on inspection the fluid was noticeably darker and had black bits in it. Thinking a seal was going i stripped and inspected the Master / Slave cylinder but the only thing i found was some signs of heat on the slave, put it all back with fresh fluid /seals plus a heat shield on the slave and it fixed the clutch issues.

Just to add, i suspect it was my Stainless manifold for the simple reason the same car went through engine mounts on the exhaust side every six months or so, i also found the cover on my alternator had seen excessive heat too. Which is why the Stainless manifold was replaced with a ceramic coated one and the 'heat' issue went away.

[Maulden7]

I agree with the above comments re the heating effect on the slave cylinder, & experienced it myself (discoloured fluid & black bits)

The first indication was intermittent loss of the clutch (pedal went to the floor but returned quickly after a few lifts with my foot) & in fact the rubber seal in the slave cylinder was probably turning itself inside out but then returning to the correct shape with the pressure - but whatever it was very soft)

I also have a large bore stainless steel exhaust which caused heat effects in the engine compartment (solved with some self adhesive heat reflecting shielding material)

Fitted a new slave cylinder (cheap & easy) & installed a simple heat shield (there have been a couple of threads here about this)

Dave M.

[c.garde]

Thanks for all feedback.
Seems to be consent that heat is involved .
and the slave IS very close the exhaust
This however does not explain the fact that during the first 30 years I never had this experience . When new I had to go up on size of MC to get the clutch to work properly . But that was my only clutch issue . ( apart of several rebuilds of the slave cyl.)
I later found out that the cause of that problem was a poor assembled 5 gearbox with too much axial play in the inputshaft.
When eventually I rebuild my LH sprint I found the piston seal in the slave VERY rounded off , lip totally gone. But still it did work , cooking and all , and NO black fluid.
Wanting to avoid cooking of seal in the future I have now build a centre bearing system. ( saab 900 ). Works very nice , but the blackening of fluid does worry me.
I know that there are other members who had done this conversion . Comments , please ?
Searching on the net I have found that the problem is common.
MX 5 and Mustang to name a few.
For now I think that poor seals are the source. After all how hot is the bellhousing/ concentric slave / gearbox? I would think nothing compared to the close proximity the exhaust of std issue .
When I address this problem I will take a close look at the fluid in the feed hose adjacent to the concentric slave cyl.
Taking in account the poor quality reported on many different rubber components ( rotoflex, gaiters ...) why not include seals ?
Best regards c.garde

[denicholls2]

An important factor I don't see mentioned in this thread is whether or not the parts you installed were manufactured at the same time as the ones you replaced. People love NOS stuff, but in deterioratable consumables that is not a plus.

Back in the day, a lot of this stuff came packed in cardboard boxes and not in plastic bags. That "NOS" stuff is just as old as what you're replacing, it just hasn't had the friction wear. There's no good reason to think it's still got a useful lifetime in it just because it's never been installed.

If it's bagged, then you can expect a much longer shelf life, but age is always a factor with unstable materials like rubber and synthetic rubber.

My 2000 Audi Avant had a rubberized coating over much of the cargo area. By 2012, that coating had turned to a sticky powder, almost a goo. What seemed wonderful when new didn't stand the test of time. So it is in our modern synthetic material world. Unless the components are being manufactured new and packaged away from deteriorating influences, they may not be the safe new parts we think they are. Keeping suppliers interested in supplying new consumables is an important aspect of groups like this one.

[miked]

I have paid a premium for brand new slave rubbers from a very reputable classic brake company. All packaged up right and still had problems. Mike

[patrics]

Hi,
Is it a problem?
Isn't it just carbon black coming out of the rubber?

Regards
Steve

[david.g.chapman]

I am near the end of changing the seals in my clutch master cylinder, as I have had black fluid developing this year. The "blackness" was denser in the master cylinder as I took it apart, but nothing came off the seals when I rubbed them.

My slave was done less than a year ago so I am assuming its not that.

I think in my case that as the master was leaking anyway, some contamination got into the fluid via the seals.

I will know more when I fill with fresh fluid and try it out.

I wonder if the rubber pipe could be the cause of our troubles? I will let you all know if I find anything definitive.

Dave Chapman.

[Craven]

Maybe it?s dissolved Aluminium Oxide.

[JonB]

Watching this thread with interest. I have black crud in both master cylinders, and will bleed the lot to refresh the fluid, as well as fit a heat shield between the clutch slave cylinder and exhaust.

[JonB]

Maybe it?s dissolved Aluminium Oxide.

Unlikely - Al2O3 is white: https://en.wikipedia.org/wiki/Aluminium_oxide

Regarding the heat shield, should I mount it on the pipe or bell housing? It'll be made of stainless steel sheet.

[Grizzly]

Funny thing is if some one had said to me their Brake fluid was dark or black i'd say that was moisture (being Hygroscopic and all) but it's automatically ruled out due to the time scale involved (wouldn't expect it to do that so quickly) but have you done a refract test to rule it out??

[JonB]

What's a "refract test"?

I would think it easier to just change the fluid. After all, I have no idea when it was last done.