How To Match The Gearbox Fd To My Diff?

[DamEscort]

Hi peeps i've done a search around the forum and cant find the answer.

What i would like to know is how to work out the ratios to match a gearbox to a diff.

My current situation is i've bought a gearbox and diff to fit to my UK impreza, checked the number on the box to confirm it is indeed from a UK spec 1996 Impreza and i was told the diff i got with it was from the same car.

Stripped the backplate off the diff today to double check what i'd been told and when i divided the number of teeth on the crown wheel (39) by the number on the pinion (11) it came out to 3.545.

Now according to the gearbox chart the final drive on the box (TY752VN4BA) is 4.11 so should this diff not also be a 4.11 ratio to match the box or am i just not understanding and working it all out incorrectly

Would really appreciate if someone could take the time to explain how it's worked out if i've got it wrong.

Cheers David

[andysti78]

Hi mate just googled "final drive ratio" try it and check out the wiki result. You need to find the diameter of the two gears to work out the correct ratio