The Capri 4cyl master cylinder is shorter than the V6 master cylinder. The reservoir mounts are different too. Girling reservoir is L? 3 the V6 is l?4. The ratio of bias from front to back breaks is different to account for weight. Our master cylinders for V6 had a 50/50 ratio. The South African master had 60/40 and doesn't stop as well as ours. The seal kits for SA and Oz Capris are different. As for internal seals from V6 to V4 they may be the same although the stroke is different which might not affect the overhaul kit but I don't know that answer.
Brakes are one thing you want to get right.
I found this out Bernie as you say sending my boosters in for updating with master cylinder attatched. When they came back the masters were missing and I got sent one V6 and one 4cyl one. I was not happy at all!!

Ergo the desire for a brand new Master..............you eliminate 99% of the bull**** dealing with so called "brake specialists"

I got my booster changed in the Perana. It has always been known for bad brakes. It came with standard V6 and uprated pads. Perana is only 9kg of extra weight to a V6. I must keep it original though.
So rather than change much their is a company I know and I'm sure others here do that from what I believe put a double diaphragm Volvo set into the original Capri booster increasing it's power. The Perana stops so much more confidently with it installed. It still has the original master (now Oz not the SA) look. The booster is the same look too but it all works better.

Books say ALL Cortina TC to TF Master Cyls (MC) are same bore as our Aussie Capri.....ie 20.64 mm
 
I wonder if anyone knows when TC TD TE or TF transformed from Imperial MC Tube Nuts to Metric ?
........and if all our Mk1 Capris MC Tube Nuts were Imperial, or did we transform to Metric in 1972 ?
It's worth pursuing as I'm overstocked with Cortina Br Ma Cyls and theyre Genuine Girling from UK and wont be changing
the oem formula for protocol integrity.
 
Thanks Keith for the great clue on Volvo DD for Vac Booster as I'm sure mine needs doing.........

Wiggy333
The Capri 4cyl master cylinder is shorter than the V6 master cylinder. The reservoir mounts are different too. Girling reservoir is L? 3 the V6 is l?4.

What's your source for that?  The parts book shows that for the dual circuit systems, the booster, reservoir and master cylinder are the same for all.

 
Yes Steve, all my PBR & Girlock books show same as you say

Just that booster is the same. The master cylinders different. The parts book refers to 69 and 70. After that the V6 was different. Bore was the same stroke was different. You can't stop a heavier car with the same mechanics. Only my memory and removing a few. I need the newer 71 to 72 parts list to prove it. I may be wrong but not unless many of my cars were messed with.

My parts book is dated 11/73.  Callipers are different which would have given different braking force.  Stroke is not relevant to pressure.

Wiggy333
 I need the newer 71 to 72 parts list to prove it.

The 11/73 version is on its way Keith!

My Aust PBR & Girlock Parts Books say ALL Capris, 4 & 6cyl, ALL used same Master Cylinder Repair Kit K7413X proven with same part number 20.64mm bore (13/16")
 
PBR and GIRLOCK both called the Master Cyl p/n as   64066631
 
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Wish I could find someone with tech drawings of ALL Capri, Escort and Cortina Masters 1969 to 1973 as fitted to our Ozzie assembled models, showing ALL dimensions comprehensively
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"Books" say early ones (69-70) had rear wheel cyls of (0.75")19.05 mm bore, #P4851, with narrow Shoes.
 
and ALL subsequent models to 1973 are (0.70")17.85 mm bore #P6984 matched with wider Shoes too