After noticing that the wifes 70 Spitfire brakes seemed to require a
little more pressure to stop that I thought they should, I figured that I
would look them over - It has been about 6 years since I built the car, and
they would most likely need some attention anyway
I had another tandem master that I had rebuilt some time ago, but when I
looked at it it had a .70 bore, so I thought that it might be a GT6 master.
Back to the car to remove the one off the car to check it out. Hummm, it
too is a .70 bore, so I did a little research and found that there appears,
or may be two types, a 5/8 bore and a .70 bore (which is what the GT6
uses). On top of that the rebuild kits are listed as different for the GT6
vs. Spitfire MK3/4 tandem master, which leads me to believe that something
is different, and that I may have a bunch of GT6 masters - but how do you
tell?? The casting numbers on the side of every one are different
basically 64676764xxx, x being the different part of the casting number.
One has 041, 03, and one has 018 but all are .70 bore. Is there a 5/8 dual
master for the MK3/4 Spitfire? I haven't pulled the one off my 72, which
is original to see what size it is (maybe I should check it to make sure it
isn't going bad as well, since I've had a rash of master cylinder problems
as of late, just rebuilt the leaking GT6 and now this...) The .70 bore may
explain why the pressure required was a little high to begin with. A 5/8th
bore would require a little less pressure, albeit slightly more travel.
All the ones I see listed new have .70 bore, and the later Spitfires use a
.70 bore, (but the fittings and reservoir are different for the later unit).
On a side note, the one I removed from the car is toast, a surprise to me.
I have used Silicon fluid from day one when I built the car, and the
secondary piston/spring/valve assy was rusted solid and the bore was
ruined! I was under the belief that Silicon fluid was NOT Hygroscopic
(meaning that it did NOT absorb water), so where did the water that rusted
these parts come from?? Never had glycol based fluid in this car from the
start - Now the GT6 master seals were shot, but the parts were clean as
ever, and that system originally had Glycol fluid in it but when I did the
Spitfire about 6 years ago, I flushed the system in the GT6, replaced the
lines with braided, and used Silicon in it as well So that all my cars use
the same fluid. It was a little disturbing to me...but that is for another
thread - I will still use Silicon, if nothing more than to prevent the
paint from being ruined when it does leak. I just may flush it every four
years or so
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