>
>On Mon, 8 Aug 1994, Dave Chu wrote:
>
>> I'm about to replace the master clutch cylinder on my 78 Spitfire. I just
>> want the list's opinion whether to switch to silicon fluid or not. If I'm
>going
>> to use silicon, the clutch system would have to be flush. I'm currently
>using
>> DOT 4 and inorder to take full advantage of the benefits of silicon I have
>to
>> remove all traces of the old DOT 4 fluid. I have hear that rubbing alcohol
>> can be used to clean out the system. Has anyone tried or hear of this?
>
Chip Old replies:
>I use silicone fluid in the clutch hydraulics on my TR4 with excellent
>results. I installed it when I had to do a complete rebuild of the
>system a few years ago (rebuilt the cylinders, new hose, thoroughly
>cleaned tubing). I still use Castrol GT/LMA DOT4 fluid in the brakes,
>but will probably switch to silicone if/when I ever need to rebuild the
>entire system at the same time.
>
>Alcohol is excellent for cleaning disassembled brake and hydraulic clutch
>parts, but I don't advise trying to flush an assembled system with it.
>There's too much chance of not getting all the alcohol out, which would
>be a lot worse than not getting all the old DOT4 fluid out.
>
>The best choice is to disassemble the whole system, clean it with
>alcohol, blow it all dry, and reassemble it with silicone fluid.
>
>Second best is to pump out as much of the DOT4 fluid as possible, then
>flush it with silicone fluid. This will get most of the old fluid out,
>but since silicone fluid and DOT4 fluid don't mix there may be a few tiny
>pockets of DOT4 fluid left after the flushing. The clutch hydraulics will
>work fine if there is a little bit of DOT4 fluid left in the system.
>However, the DOT4 fluid will continue to absorb moisture, so where ever
>those pockets are will still be subject to rust or corrosion. If at all
>possible, disassemble and clean the whole system before installing
>silicone fluid.
>
I too use silicone fluid in the brakes and clutch circuits of my Big
Healey. A couple of suggestions:
1. I would not use rubbing alcohol to flush a hydraulic system. The
"off-the-shelf" stuff is usually 70% Isopropyl Alcohol (IPA) and
30% water. Why put ANY water in a hydraulic system? One of my
father's restoration magazines suggests using denatured alcohol
(ethanol with benzene added to make it poisonous) to flush the
system. If you want to use IPA at least get the stuff that's 99%.
2. First, drain the system of all glycol-based fluid, then "flush" with
compressed air for a while (at least 20-30) minutes. Then flush with
denatured alcohol, then air again. Then add the silicone fluid
and flush some more when you bleed the system.
3. Silicone fluid can be hard to find at the local parts houses. I'd
have at least a quart available.
Regards,
bs
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