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Discussion Starter #21
I'm the second owner of this SS and the MC that's on there now is the one it came with when I bought the car, but I don't know if any modifications took place before my ownership. The Girling part number appears to be 64674975. If I recall it's a 3/4" MC, and as mentioned it has the wider 2.225" mounting lug.

Returning to my initial query, I'm thinking of rebuilding it for good measure since it's out on the bench and then put it back in so that I can enjoy the car until I have a conclusive answer regarding a suitable dual circuit unit. Does anybody know the correct part number for the rebuild kit for a Girling 64674975?
 

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Hi ascari,

Does your car have discs?
The mc for the disc brake system would be 3/4" indeed as in the Girling catalog.
The mc of the SZ with discs is also 3/4" but would be different from the SS/ Spider with discs, it has another body.
So could you show some pictures here of the MC that you think is the original one ?
Then hopefully I can give the correct Girling MC number and rebuild kit number.

Rgds,

Thierry
 

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FWIW, it's been a long time since I dealt with brakes, but I seem to recall that 2 things matter with respect to brake effectiveness, pedal forces, and pedal feel:
  1. The leverage ratio between pedal pad and master cylinder (as defined by the lengths between pedal and pivot point, and pivot point to master cylinder).
  2. The areas (and ratio of areas) of the cylinder surfaces (as defined by the diameters of master and slave cylinders).
So, in order to keep the ratios between master and slave cylinders the same, it's conceivable that, in a single circuit to dual circuit conversion, the diameter of single 3/4" master brake cylinder can or should be reduced to a 2 * 9/16" or more likely to a 2 * 5/8" dual cylinder (following the formula (3/4" * Pi) / 2 / Pi = roughly 0.5890"), assuming the slave cylinders stay the same.
 

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Hi ascari,
Thanks. As told before, with discs, the 3/4" diameter is for the SS and also for the SZ but the mcs and the corresponding repair sets have a different Girling number in the book.

Once you could show some pictures of the body I would have an idea of the correct mc that I have to look for and send you the Girling numbers for the mc and for the repair set.

Rgds,
Thierry
 
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