After tons of speculation on Slave and how much fluid it contains and does it leach black from the rubber...

I have taken my old slave apart to prove once and for all the Slave contains VERY little fluid at all and does leach black from the rubber.

Ok here is a shot of the full slave.


Here is the Slave disassembled without the throwout bearing but just the Plastic plunger that rests on top of the thick rubber piston that the fluid pushes on. The inside edge of the plastic piston is all that makes contact with the rubber piston in the picture below.


Understand that this setup is the reverse of what one would expect. A hard aluminum piston with a rubber seal around it. In this case the piston IS the rubber seal. Here is the seal pulled up


Here is proof that the black leaching is from the piston.


Here a shot of the size of the hole that the fluid enters. Its the same on both sides and it opens to a small channel under the rubber piston


Here is a pice of wire showing the entry point of the fluid.


Now for the question, how much fluid does the slave hold? EXACTLY 2 TABLESPOONS. Yes I used wifeys cooking measuring spoon.
I filled the whole thing up with water and plugged the holes.


I poured it out into a plastic dixie cup..to further demonstrate how little there is.


There you have it.. There is no more magic in the slave...the curtain has been pulled aside...

 

Much appreciated Chuckster.

Please continue the experiment.

Clean up that rubber seal.

Then cut it in half. Insert half in fresh DOT3 brake fluid, cap the container; and insert the other half in fresh DOT4 brake fluid, cap the container. Report back in a week on whether the color of the fluid in either container has changed.

Many thanks.

Ranger

 

Ok..Will do.. I will need to shake the container occasionally.. Because I am sure it's the rubbing up and down that make it bleed..

Keep in mind as per the pictures.. The inside and outside of that seal are under a lot of friction rubbing up and down against the aluminum walls.. That alone would cause enough abrasion to release black particles.

But I am gonna see if one type of fluid causes more softening or leaching then another..

 

Chuckster, you are my hero.

Interesting dissection. The volume of fluid doesn't surprise me since it's displacement of an incompressible fluid over a certain distance that does the work and the necessary travel is obviously there. I dislike the setup the M6/12 have for the master/slave and the difficulty of flushing the system.

Keep us posted.

 

One more thing.. you can clearly see after I cleaned it up where it was wearing most..

The shiny rubber edge on the bottom half is the bottom of the slave where the fluid is. The dull worn edge on the top half is where it makes contact with the throwout components.

 

Awesome work Chuck!!

 

Here's a question, suppose the rubber "piston" stops sliding and starts to roll instead. Do you think this is possible based on your observations? If it stops sliding I would think it might start hanging.

 

Thought #2, suppose you machine a metal piston with two o-rings and let that provide the piston action.

 

I imagine it would be feasable but not likely.. Because it is only fluid on the backside and the would exert pretty consistent pressure all around. Also the shape of it would not be conducive to a roll over.. Also if it rolled it would lose the seal and immediately spew all the fuid out. All 2 Tablespoons full

But I'd love to see someone pull apart a slave the experienced pedal hanging...

 

 

Thanks buddy, I appreciate the comment...:o

 

Many years ago I had a summer job in a rubber plant. The black that you see leaching out of the rubber is carbon black which is one of the materials used to make rubber.

Bill

 

Also means that for those flushing with a remote bleeder.. Just pump enough to fill the reservior once..

I can also see why folks get great results with the Mighty Vac bleeder.. Just need to suck hard enough to pull the rubber piston flat on the bottom of the slave..

 

Let's not get carried away here.

Anyone ever bleed the brakes after 3-4 20-minute sessions? Why does the fluid at the caliper get grossly discolored? Heat play a role in that color change?

Aggressive driving can bring the temperature at the slave to 400+F. That cooks the fluid, discoloring it.

Chuckster, Would be good were you to measure the fluid capacity of the hydraulic lines, the combination of the master and slave. We know the capacity of the slave itself and the reservoir.

Chuckster, which version of the slave it that? From memory, the C5 hydraulics were revised in 2001. Is that the original slave from your MY 2000 or the replacement from your later clutch swap?

Ranger

 

WOW !

Chuckster, I know it slows you down when stopping to take pics of work like that; and THANKS for doing so

you just made it easier for everyone else.

 

The lines will carry very little fluid as the insides are about the size of that wire I used to show the entrance to the slave.. All I have is the lower line.. I did not save the master or the line from it.

The turkey baster can easily measure the contents in the reservior and add a few tablespoons for the line + 2 tablespoons for the slave.. I am guessing the master cylinder hold the same amount of fluid that the slave does or else the master would over drive the slave..

The Slave is from the 1st time I had the entire system replaced by the dealer.. I had it done around 2003.. So it may very well be the redesigned one.

I have the latest slave design when I had the Cartek installed..

 

I recently dissected the slave assy off of a 30,000 mile, 2000 C5 coupe (with a ProCharger). I also was dumbfounded by the small capacity, but not surprised by the somewhat compromised design based on its location, and lackluster performance.
On this particular unit, there were grooves wore into that inner sleeve where the plastic collar (that pushes on the throwout bearing) has been riding, and possibly binding up when, either, expanding from the heat, or getting slightly cocked from uneven force transferred from the hard rubber O-ring.
Part of this system's problem is the multiple contact points required for an engineered chain reaction. The fluid needs to accumulate, equally, pushing on the seal/O-ring, this rubber seal then compresses slightly before moving (making it grab the inner and outer sleeves even tighter creating more resistance to the hydraulic force), then pushes on the plastic collar that is probably (at some point) rubbing against the inner sleeve, which is locked onto the throwout bearing that has to accelerate with the pressure plate as it forces the bellville fingers against their loaded state. With the great amount of heat transfer and the small amount of fluid usage/displacement, it is a wonder that it even works (not to mention the mechanical pedal and hydraulic master cylinder/piston part of this equation).
I find it hard to believe the aftermarket has not yet come up with a much improved version of the slave and its inner workings.
Leaching from the O-ring is a legitimate assumption, as this black substance accumulates inside the slave's crevices and floats independantly of the fluid's concentration. This adds to the degradation of the seal/O-ring, which could create more drag/friction where it contacts both sealing surfaces, alter its expansion rate (lower its resistance to compression), and create inconsistencies in its lubrication as the O-ring 'gives way' during movement.

Kudos to Chuck for the good pics and useful tech.
Sorry for the partial hijack.

 

Wait, that should read "again, proof-positive that the GM TSB is correct (heck, they only designed your car) instead of YOUR theory that the fluid turning black is heat-related, despite numerous eye-witness postings to the contrary "I just changed my fluid and simply drove around town, no hard runs, and my fluid is black again".

Folks will respect you more if you acknowledge the manufacturer and first-hand experience. It's starting to feel like you have stock in brake and clutch fliud compaines.

P.S. - Even though the seal in the slave cylinder may in fact leech, the discoloration we are seeing is most likely coming from the master seals (same materials in use), not the slave. It's not like the fluid is constantly recycling.

 

For the sake of discussion, let's assume your explanation of the mechanical chain reaction is correct. What changes to those mechanisms would occur inside the slave if its temperature exceeds the actual boiling point of the clutch fluid?

TIA,

Ranger

 

Might want to try reading the recent GM acknowledgments of the role degraded fluid plays in pedal woes. Here is one quote; you can dig out the rest...

By your theory must be pesky seals that can turn fresh clear brake fluid very dark in three 20-minute HPDE sessions, rather than heat like the racing community has believed for at least 40 years.

Ranger