discolored fluid in clutch mc

[Grizzly]

What's a "refract test"?

It's a test to see how much moisture there is in the fluid, most garages do this to check if there is a fault making the fluid dark or just old fluid with lots of moisture in it.

optical refractometer is the old school way of doing it, i believe there is a pen type electrical device https://www.ebay.co.uk/itm/ELECTRONIC-B ... SwpDdVAApH but i've never used one of those.... I also believe a similar test can be done using a Multimeter but never done it so you would have to google it.

[elanner]

From my experience with my brake master cylinder and fluid I'd agree with others that it's the seals. New or NOS. A case of Occam's razor. You're going to have to keep changing them until you find some of the required quality.

I've always been curious about how much the fluid actually moves around a hydraulic system. How long does it take for the fluid adjacent to a failing seal in the slave cylinder, turning it black, to show up in the master cylinder? Surely a long time? In other words, does the column of fluid in the hydraulic pipe simply move to-and-fro in a relatively fixed column, or does it somehow get continuously mixed up?

So what I'm trying to suggest is that if the fluid in the master cylinder turns black, suspect the seals in the master cylinder. The only way you'll know if the seals in the slave cylinder are failing is when it starts leaking or the seal expands to the point that the piston locks up.

Nick

[Chancer]

this tester allow you work distant limit free and don't need to worry about your swirly line.

Thats a relief

[JonB]

The only way you'll know if the seals in the slave cylinder are failing is when it starts leaking or the seal expands to the point that the piston locks up.

Couldn't you just bleed it a bit and see what colour the fluid that comes out of the bleed nipple is?

[elanner]

Oh yes - duh. Of course. But you'd need to be the curious type to randomly take a peek. Not like simply taking the cap off the master cylinder!

[miked]

Re: Fluid movement and fluid discolouration.
When you press the pedal for the clutch the Res' is closed by the piston end seal and fluid moves from the master into the slave. That volume must then return back to the master cylinder bore when the piston in the master cylinder bore retracts. The Res' is then open to whatever colour fluid returns back, so it can mix IMO.
The slave cylinder piston retracts with its spring and that of the clutch pressure plate so is at it's least filled position when clutch is not pressed. That's why I think it gets back. Heat damaged slave cylinder rubber debris. Also proven by eventual dribbling of the slave cylinder telling me that it is that time again.

Mike

[Bigbaldybloke]

Am I right in thinking that dot 5 brake fluid is not hygroscopic so would changing to that be beneficial if people think it may be water vapour getting into the fluid causing this problem. Are the seals compatible with dot 5 fluid?

[ElanDNA]

beAm I right in thinking that dot 5 brake fluid is not hygroscopic so would changing to that beneficial if people think it may be water vapour getting into the fluid causing this problem. Are the seals compatible with dot 5 fluid?

Hi
Yes, you're right.
DOT 5 is a silicon brake fluid and you ca'nt mix with others!!
Is the all system new, you can take it. I have it more than 25 years in my brake and clutch system.
Only one times changed.
This fluid is a little kompressible? and gives me a somewhat "elastic feeling" in the Pedal.
Silicone is a good lubrication, better than the other brake fluids.
In the early '90, I can't buy it easy in Switzerland. Then I get it from the Harley scene.
Only the slave cylinder was cooking and died in 2015.
Then i'v made a heat shild and a new cylinder from stainless steel. And of course new brake fluid.
Urs

[Grizzly]

As above... I believe you can change from Dot 3 to Dot4 without a thorough flush but dot 3 or 4 to dot 5 requires all the old residual fluid to be removed and well flushed through. Dot 5 isn't just good due to lack of moisture absorption but it also won't take your paint off if you spill it.

One thing to be aware of with Dot5 is because it doesn't absorb water contamination is a much bigger issue (one of the reasons you need to prep the system well) also don't be fooled into to thinking dot 5 and dot 5.1 is the same... They can't be mixed either.

At work we use Motul RBF 600 Dot 4

[prezoom]

Plus 1 for Motul. Best fluid I have ever used. Still have some un-opened metal cans of the blue stuff.

[MarkDa]

JonB
Heat shield is probably easiest bolted to bellhousing, that way you won't have to separate pipe line and rebleed .
Mark