Black Clutch Fluid

[david.g.chapman]

I have been suffering this for some months now, and was beginning to suspect the flexible pipe in the hydraulic line.

Then it dawned on me....

I had taken the slave cylinder out last year and de-scratched the bore with 600 grit paper and then 1000 grit. It worked really well and stopped the leaks with a new seal. I must have removed some plating though, so what I am getting now is probably an aluminium deposit, similar to using metal polish.

Does anyone know of a way to stop this without replacing the slave cylinder?

Dave Chapman.

[mbell]

I would have thought it more likely the rubber seals breaking down a little and contaminating the fluid. There have been quite a few reports on the forum on black clutch fluid.

Potential course of actions:
- Ignore it until you have clutch issues
- Flush the clutch hydraulic system and see if it comes back
- Rebuild master, slave and flush system
- Replace all the hydraulics

[david.g.chapman]

Thanks for the reply mbell.

I had replaced all of the seals in the master and slave cylinder, and while doing that had replaced the fluid with more DOT 4. The blackness returned afterwards. There are no particles you can see, so they must be very small. My money is still on the raw aluminium in the slave cylinder abrading on the steel plunger.
It could be that these items are still bedding in after my handiwork with the wet and dry. I will try a flush again and see what happens, Then replace the slave and flexi pipe if it comes back again.

Cheers,

Dave Chapman.

[Gordon Sauer]

Yes, even the black gasket of the top. Gordon Sauer

[rgh0]

If you use wet and dry paper on the aluminium cylinders you need to be very very very thorough to clean it afterwards The particles embed in the soft metal and are difficult to remove and will then wear the seal.

cheers
Rohan

[patrics]

Hi,
I?m not a chemist but the blackening of the hydraulic fluid is probably from carbon black leaching out of the rubber components and is normal but unsightly. How much comes out, I guess will depend on the rubber manufacturer and how much rubber is in the system. In the aftermarket industry and as originally fitted the seals will probably be SBR and they use carbon black as reinforcement and even more likely to be used in the clutch system.
Modern brake systems tend to use EPDM rubber which still uses carbon black but maybe less or better cross linked so doesn?t tend to leach out. Nothing wrong with SBR rubber.
If you haven?t already done so you could change hoses to PTFE lined type which I think will help a lot.

Regards
Steve

[david.g.chapman]

Thanks again for your responses.

I should have said - I finished off my wet and dry rubbing with a good going over of T-cut and a kitchen towel. This bought up a "mirror" finish on the bore, and it certainly felt smooth to the touch. However, I am alerted to the possibility of wear on my new seal.

From what you all have said my suspicions are now leaning towards the flexible pipe. I will have a look at this when I have finished my other winter jobs, and as always, will post something if I find anything definitive.

Dave.

[nigelrbfurness]

+1 for the flexible pipe. If I may hijack the thread, can anyone recommend a suitable thread sealant for hydraulic fluid? One of our vehicles has a clutch slave cylinder that is in two sections that screw together concentrically and it is leaking fluid at the joint. The thread is too fine for thread tape, which may not be resistant anyway! Thanks in advance.

Nigel F.

[patrics]

Hi Nigel,
There should be never be a need for thread sealant - so something is wrong, either pipe flares not formed properly or fittings worn out.

Regards
Steve

[rgh0]

Loctite 542 - hydraulic thread sealer

cheers
Rohan

[nigelrbfurness]

Thanks Rohan, I'll order some.

[nigelrbfurness]

Hi Nigel,
There should be never be a need for thread sealant - so something is wrong, either pipe flares not formed properly or fittings worn out.

Regards
Steve

Steve - Thanks for replying, the leak is actually in the slave cylinder body, not the pipe work. The throw of the slave rod is adjusted by screwing the body sections in or out. However your comment that the parts might be worn is probably correct but as the slave cylinder has been unobtainable since 1968 I have to try and "make do and mend"!

[patrics]

Hi Nigel,
You should be able to buy new, I did a few year a go and still made in the original factory in South Wales
I will check after Christmas.

Regards
Steve

[fatboyoz]

Hi Dave,
If you still suspect that it is the bore of your slave cylinder that is deteriorating, you could have it sleeved in stainless steel. I had both masters and slave cylinder done a few years ago.
Merry Christmas,
Colin.

I have been suffering this for some months now, and was beginning to suspect the flexible pipe in the hydraulic line.

Then it dawned on me....

I had taken the slave cylinder out last year and de-scratched the bore with 600 grit paper and then 1000 grit. It worked really well and stopped the leaks with a new seal. I must have removed some plating though, so what I am getting now is probably an aluminium deposit, similar to using metal polish.

Does anyone know of a way to stop this without replacing the slave cylinder?

Dave Chapman.