>I am about to flush my brake and clutch and put in silicone fluid in. What
>is the best way to do this and get the clutch bleed right?
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Kevin (cc'd Triumphs and Spitfires also)
Before you do this you may or may not find my observations interesting, so
I'll post them for your own conclusions. . .
About a year ago I decided to replace the fluid in my Spitfire clutch
system with Silicon (Dot 5). I had already done a complete rebuild of the
braking system about three years prior and used Silicon in this system
without incident. Brakes are solid, without any soft pedal feel, just like
I had it when it was filled with Dot 4. The clutch system in this
particular car is comprised of a stock Girling Spitfire master, solid metal
pipe (no flexible hose as per Spitfire) and a Ford Courier (Mazda) slave
cylinder.
When I did the brakes it was a complete rebuild, new rear wheel cylinders,
front caliper rebuilds, new flexible hoses, and a brass re-machined (Apple
hydraulic) master cylinder, rebuilt. Metal hoses all flushed out with
brake cleaner, and compressed air so that basically I started with a clean
slate. I did the same with the GT6 and to date I am completely satisfied
with the "conversion". Firm pedal same as before and the fluid is clean
and clear, none of the usual murky discoloration/deterioration of the fluid
that was so common with the original Dot 4 even after over three years of
everyday use.
So I figured that the clutch should benefit from this fluid ("fluif" for
all you list veterans). This time though, no rebuild just flush and
refill. Since the system was rebuilt around a year prior I figured that it
was fine and in fairly good shape ( I wasn't having any problems and I was
going to remove the tranny cover for something else so access to the slave
would be easy). I had completely overhauled the brakes because of all the
discussions at THAT time, and the horror stories of converting I had
already read. Later on, after hearing about just flushing and refilling
of some individuals, and comments that they had experienced no problems
doing this, I thought I'd give it a try. Besides the clutch isn't as life
threatening as a brake failure could so, happy at the prospect of a little
less work in converting, it was worth a shot in my book. I completely as I
could, drained all the Girling Dot 4 out, flushed with brake cleaner,
compressed air (several times), and when I was sure that all was clean and
dry, refilled with Dot 5 Silicon. All was well for about six months. Then
I noticed a slight problem with holding the clutch out for extended periods
during hot days in heavy traffic. It felt as though I had a leakage
problem in the master. No fluid loss, just slowly losing the clutch
(engaging nearer the floor). It worked fine most of the time, just these
extreme cases which meant. . .getting time for a rebuild. I suspected that
the fluid switch may have had something to do with the more rapid than
normal deterioration of the seals.
I ordered kits and completed the rebuild just last weekend. What I noticed
upon disassembly was that (as suspected) the master cylinder piston seal
was very soft (and I did notice more than a few small black particles in
what was otherwise still very clean fluid). What was also of interest was
that the smaller seal, the one that blocks the hole at the end of the bore
in the cylinder. You know, that small cup shaped one at the very end, was
almost falling apart and was much softer than the even the main piston
seal. I'm talking about the inner cylinder seals here not anything outside
the cylinder that isn't touched buy the fluid. The slave cylinder seals
didn't seam to be as affected by the immersion in different fluids as the
others, but still showed some evidence of leakage as the outer boot
contained a noticeable quantity of fluid, much more than should be there
anyway.
My conclusion was that the seals, exposed to the different fluids,
exhibited different swelling and deterioration because one can't COMPLETELY
remove all the fluid, especially the stuff that the seals themselves absorb
and therefore damage resulted from this exposure. This time of course I
rebuilt everything as new, and refilled with Dot 5 and all is well. This
isn't meant as an endorsement of any particular fluid ("fluif"), but for me
Dot 5 is what I will continue to use. It doesn't seem to be as harsh on
the seals and the fluid remains clear (indicating to me at least) that less
wear on the seals may be occurring. It does however, at least in my case,
indicate the need to use all new or rebuilt components if changing between
these specific types of brake "fliuf's" :-)
Barry Schwartz (San Diego) bschwart@pacbell.net
72 PI, V6 Spitfire (daily driver)
70 GT6+ (when I don't drive the Spit)
70 Spitfire (long term project)
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