Saturday, September 20, 2014

Rebuilding Clutch Slave/Master Cylinders

I've been working on rebuilding the clutch and slave cylinder.  Most people don't bother rebuilding for a number of reasons:
1.  Rebuild kit availability isn't great.  There used to be a greater supply of seals but not lately.
2.  Pitting in the bores from corrosion is a major cause of seal destruction.  The cylinders are cast iron and rust easily when brake fluid is left for a long time and moisture is present.  It doesn't help that the master cylinder is vented to the atmosphere, allowing moisture to get into the fluid.
3.  There are cheap replica master cylinders and slave cylinders on the market.  I wouldn't call the master cylinders reproduction since the "Benditalia" raised lettering is replaced with "DeTomaso" and the pistons differ significantly.  Unfortunately, these units are notorious for failing prematurely.
4.  Actual replacement master cylinders are available from Italy, at a price that isn't too bad.
5.  Stainless steel versions of the slave cylinder are available but are expensive.


My reasons for rebuilding the cylinders are:
1.  I can rebuild them for a fraction of the new replacements.
2.  I can have both slave and master cylinders sleeved in 304 stainless steel, keeping a stock appearance with superior corrosion resistance.
3.  Seals are available if you know where to look.

I found replacement slave cylinder seals from a tip on the Pantera email forum.  A fellow Pantera owner rebuilt his using seals and backer rings from a hydraulic seal company.

Here is the slave cylinder piston and new seals.  I've stripped off the rust from the slave cylinder.  The rubber boot and spring are in good shape, not needing replacement.


A close-up of the new seals.  They are too thin, requiring a 0.070" backer ring.


Here's the interior of the slave cylinder bore after honing.  I think it needs to be sleeved.


Here's a close-up of the piston with the backer ring.  Notice the lips point away from fluid pressure.


I found replacement master cylinder seals at International Auto, a company specializing in Fiat/Alfa Romero stuff.  Here's a breakdown of the original and replica master cylinders.  I like the zinc plated spring, but the piston and seals were in worse shape than the original, yet it's brand new!  The bottle reservoir is molded crooked and the cap is not even close to the original cap.



To be continued...

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