I've been measuring up to order my prop shaft, from Bailey Morris.

I'm struggling to find any information online about the standard Ford diff pinion flange sizes, really for piece of mind to confirm the dimensions i'm measuring. Specifically - i mean the flange which faces the gearbox.

The Bailey Morris kit-car prop shaft order form suggests to me that a '109mm', 10.1mm bolt, 4-bolt 90mm PCD pattern is a standard flange.

As my diffs in situ i've tried my best to measure the PCD across the bolt holes - but access is not great.

The diff flange has 4 plain holes, and 4 threaded holes. I think the threads are M10 fine thread.

Across the outsides of the bolts I measured 99.64mm and 98.59mm - so with a nominal 10mm taken off for the bolt size, to get the measurement across the centres, I get 89.64 and 88.59. Is this close enough to be 90mm PCD?

I can't upload pics - but hopefully these are visible from my Googledrive, showing the verniers in place against the two pairs of threads:
https://drive.google.com/file/d/12eZ7esk0u9CDlModTDyoFGoyQSY-X6cY/view?usp=sharing
and
https://drive.google.com/file/d/1yU0qEnNeLEHyfIQWBLyqEI1eOuD38YoB/view?usp=sharing

I measure the outer diameter of the flange itself as 107mm, but it does have a thick coat of paint on it, and doesn't directly match to any dimensions i can referred to online...

Just ring them and tell them what you need, they know part numbers straight away. I went into their place and said i need RX8 gearbox to sierra diff and knew parts instantly. just need length.

I might have to do that in the end Mike - and I am sure you are right. However I'm aware that if I end up with a prop that doesn't bolt on, it'll be my fault for speccing it wrongly!

Just bumping incase anyone can add anything. Some Googling before I posted on here did turn up a couple of other instances of people asking the same question - but also without reply (one on a Westfield forum i think).

As an alternative - if I knew that Ford only made the 'Sierra' diff as a RWD IRS diff, I would have some more confidence that there was only one possible PCD for the prop to mate up to. I assume this could well be the case, as pre-Sierra everything was live axle, and post Sierra everything was FWD?

[Edited on 30/9/20 by jps]

Just to close the thread off, incase anyone in the future is looking for the same info.
Bailey Morris confirmed that the measurements I have fit a standard flange they produce - which I think they refer to as a 90mm PCD.

Measured diagonally - I do have a 90mm PCD.

However - using the method of measuring adjacent hole centres - then multiplying by a set figure, depending on the number of studs (as all online PCD calculators do)- does not give a 90mm PCD

This is because the 4 holes aren't evenly arranged - i.e. in a square pattern at 0 deg, 90 deg, 180 deg and 270 deg

By summoning up my inner child, to do a 'brass rubbing', I found that the holes are arranged instead in a rectangular pattern - at 0 deg, 80 deg, 180 deg and 260 deg.

I believe (although not confirmed) the live axle Ford pinion flanges have the same rectangular pattern. But again, reference to this online is scant.