i´m a bit confused about my diff size:

it should be from a sierra cosworth 2wd..ergo: 7.5inch

i bought one from a scorpio (i think called "Granada mk3 in UK?) which should be always a 7.5inch

than i checked this page:
http://www.super7thheaven.co.uk/Sierra_Rear_Differential

both my diffs have a long bolt on the front lower fixing, the width on the lower fixing is around 177mm on both diffs...which would mean 6,99inch. ..ergo 7" diff as i thought this lower fixing measurement indicates the diff size?

the width measured from drive-flange to drive-flange is roughly 300mm on both diffs.

so can anybody help me to identify my diff?

sorted....my mistake was measuring the lower fixing width...i should have measured the upper one....so its 193mm on both diffs. ergo: 7.5"

but another question:

the diff in the car has a rear top-mount.

my spare diff has a koala mount.

so i swap the diff-covers and thats it?

Yes that about it on a lot of kits the mount you are talking about is not used
Have a look at Google images and you will see all the different types for sierra / granada
Jacko

As far as I know, the easiest way to tell a 7 inch from a 7.5 inch one is the front top bolt
mounting hole in the casing is solid in the 7.5 inch diff and open in the 7 inch unit.




This is a 7 inch diff and you can see the hollowed out top mounting.

HTH

Good tip. Thanks