Clutch fluid black !

[tim wood]

So whilst carrying out some other work i noticed that my clutch slave looked decidedly moist.
Removed the cylinder and it was indeed beyond its best days. I replaced the master some time ago when converting from LHD to RHD.
I thought that I may as well change the flexible hose as this was likely the same vintage.
New cylinder bought and I also purchased one of those fancy remote bleed kits that allows you to move the bleed nipple to the top of cylinder and fit a short hose with a bracket fixed to the cylinder.

So with the system drained I was not really surprised to find the old fluid black and manky.
New cylinder and hose fitted without too much hassle despite limited room. Gave up with the remote bleed kit as the space to fit the banjo union is simply too tight. Maybe ok if you have the engine and box out.

Now the interesting bit.
Filled with new fluid and bled though. The new fluid also came out black ! Remember this is a newish master cylinder with new hose and slave. I used best part of of a litre of fluid until it turned clear. The fluid kim the reservoir has always been clear which to my mind means that the master cylinder must have been contaminating the new fluid.

Seemed very strange to me !

[flatfloor 3.8]

I think this may have something to do with the low pressure black rubber hoses that run from the fluid bottles to the master cylinders. These hoses break down over time and eventually sweat and leak. I think the rubber breaks down internally and turns the fluid black. No real evidence just my opinion for what it's worth.

[mgcjag]

Hi Tim....how long has the fluid been in the system.......personslly i always stick to dot 5 silicone from Automec.for brakes and clutch....no damage to paint....leaking hoses...or turning black....been useing it for over 20 years with no problems......Steve

[tim wood]

Hi, thanks for the replies.

The feed hose is Cohline about 4 Years old. Fluid I’ve used is the standard DOT 4.

Strange !

[tim wood]

Hi, thanks for the replies.

The feed hose is Cohline about 4 Years old. Fluid I’ve used is the standard DOT 4.

Good comment about the hose. Hadn’t thought of that, if I can find a spare bit I’ll change it .

Strange !

[tim wood]

I found a post on the forum from Marek with a suggestion to replace the clutch bottle with a brake one and link the sender. Sound an excellent idea and since I’ve found a spare bottle with a length of Cohline that’s what I’m going to do.

Thanks Marek !!

[Geoff Allam]

I may be missing something but how does that solve the fluid turning black problem ?

[tim wood]

Hi Geoff,
It doesn’t solve the problem other than replacing the existing flexible Cohline hose with new.

After extensive bleeding the fluid is now clear anyway, you could say that fitting a low level sensor is an upgrade.
Since I have that parts in the garage I may as well do it.

[Geoff Allam]

Sounds good.

[44DHR]

I would keep an eye on this and perhaps bleed the clutch in a few months or after a summer’s use.
My initial thought was that it would be the single black 7/8 inch diameter clutch cup seal breaking down or bedding in to the new cylinder bore. Although you said a new clutch slave was fitted, some of these replacement parts - and the clutch seals - can be of poor quality compared to the original parts.
A common issue is failure of the clutch seal when bleeding the system on old cylinders can be caused by the seal being pushed past it’s normal operating area under enthusiastic pedal travel and encountering a corroded area not normally swept by the seal causing the seal lip to fail. This is another reason to get any old cylinders - clutch or brake re-sleeved in stainless steel to keep the whole bore corrosion free, so they can become useful spare parts.
Hopefully all resolved for now.
Regards,
Dave