ok people i have a 95 wrx jdm turbo import,now the car has been throught 3 gear boxs,on buying the 3rd gearbox i was given the diff with it however after fitting the diff and gearbox the diff is leaking oil very bad and screams like mad aswell.so thinking in putting my old diff back on which had nothing wrong with it when removed, but how can i tell if it is the correct diff, i have took the back plate of both diffs and on the big cog both have 37 teeth now on the leaking diff im sure it says 4.1 in white tipex pen but not 100& sure i belive the gearbox and diff came out of a sti but was told they have the same gear ratio.but am unsure as what the old diff came out of how can i tell,like i said bith had 37 teeth but dont want to fit the old diff to find out it the wrong one please help kind regadrs ben

 

As far as i understand it mate you count the teeth one the big cog (crown wheel) and the cog with the screw type teeth that mesh's with this one (pinion) which if you look into the diff from the rear you will see the pinion at the front end.

You then divide the crown teeth by the amount on the pinion and that should give you your ratio e.g. 4.11.

David