garrett376

I thought this might be helpful for those curious what the inside of a C4 longitudinal slave cylinder looks like, as well as hopefully helpful to me and others in locating a possible source for new little blue seals to place around this piston. Think this one might have been leaking?!!

Any ideas for a parts source? I was going to start looking into brake master cylinder rebuild kits of similar piston diameter... I'll keep you all posted with what I find out - anyone have tips, chime in!

If a seal replacement is available, it will permit rebuilding this part which lists for $430, and costs $347 from a discounting porsche dealer. A $20 set of seals sure looks good at this point!

kgorman

Great pics Garrett.

I also want to find a source for seals, as I had/have the exact same issue. I rebuilt one out of extra parts from a damaged one, so I have a spare at this point. But I know I will need more seals soon.

Here is my thread linked for the lazy.. (like me)
https://rennlist.com/forums/showthre...ghlight=sanity

Red rooster

Garrett,

Is there a manufacturers name on the cylinder ? I have never looked !
That may help to narrow down a seal source.
Its a very good idea to find these .

Geoff
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KS400200,the oldest 964 on Rennlist,unless you know differently !

garrett376

I think I found a source... stay tuned....

garrett376

Ok... I'm still looking!

Motorcycle brake master cylinders are the same 16mm sized bore... it's just a matter of finding the seals to fit that piston in the slave. Anyone know of good motorcycle parts suppliers? There has got to be a rebuild kit out there that will work...

The seals are about 3.5mm wide fitting in a 3.8mm groove, and 1.5mm thick (cross-section). It looks like they'd be made of ethylene propylene (EPR or EPDM) to withstand brake fluid.

garrett376

I think I'm talking to myself, but.... think plain EDPM o-rings will work?? Those blue seals are pretty fancy with their pattern, but it seems that many slave cylinders utilize o-rings as seals, so that might be sufficient. Only one way to find out, eh? $10 in o-rings seems like a fair price for an experiment!

dfinnegan

You may be talking to yourself, but I, for one, am listening intently!

Marc Shaw

Oh, we all are but just have nothing to add but hope Garrett is successful.

Marc

joey bagadonuts

Keep up the good work, buddy!

tbennett017

you go brah'

JasonAndreas

I don't think you can substitute a regular o-ring for a pressure seal? Have you tried the Thomas Register for a supplier?

They may work in the beginning but will deform (probably sooner than later) under the pressure and end up dumping brake fluid into the gearbox.

springer3

Garrett:

You are not talking to yourself. While you are looking, the clutch slave and the power steering rack are two more parts that could be fixed if we could get the seal information.

EPR is what your pencil eraser has on the end, and I don't think it is a good choice for a hydraulic seal. You will also see Nitrile and Buna-N O-rings. Silicone or EPDM seals will tolerate hydraulic fluid, and are right for this application. I agree with Jason that a standard O-ring will probably get damaged if used in a groove designed for a square ring. The fact that you have three seals with dimples makes me think this may be a low-friction design, and O-rings might not let the piston retract properly when the hydraulic pressure is released.


To get the correct seal, go to an industrial supply house or a hydraulics shop with the old rings. Get into the line with the most experienced-looking counter clerk. Some can tell at a glance what something is, and most are good sorts and don't mind helping you find what you need. If you run to a dead end on the west coast, mail me one of the rings and I will take it to the air and hydraulics shop close to where I work.

I have already tossed my old clutch slave, but seals for those would also be nice to identify if you still have one of your old ones. I have moved recently, so PM for my new address.

Red rooster

Thats why I mentioned any makers name or similar clue on the cylinder to find the seals .
I will have an ask around back in Germany .

Geoff
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KS400200,the oldest 964 on Rennlist,unless you know differently !

RicardoD

Trying to find the exact seal that fits AND with dimples will be tough but I am listening (er, reading) and rooting for you.

If you have major concerns about matching the exact same material, I would be willing to bring a small piece of your broken seal to my work and I can have our lab guys run an FTIR analysis on it. That little machine should spit out the kind of material this is. We do this stuff all the time to identify foreign material in various failure analysis investigations that we do.

Good luck!

garrett376

That's my worry! You know it's interesting - the slave cylinder will not dump fluid into the gearbox unless you also have a failed seal in the transmission - otherwise it just leaks out onto the ground. So worst case it will made a puddle but at least the tranny won't go!

Geoff - there are no markings other than some date codes and the part number!

Springer - while the groove is flat, so is the groove where other o-rings are used on the engine: oil pressure sender console has a flat groove for an o-ring, as do the cam cross-over bridges. But those parts aren't moving! PM me your address, and I'll shoot you one of these seals to see what you can come up with. Thanks

In looking at tons of after-market master and slave cylinders, almost all of them use o-rings. And these are on some lighweight applications (like motorcycles). But I wonder about the pressure difference of a braking system vs. the PDAS...