matching diffs

[Vic Eaton]

HELLO ALL
Help needed to determine ratio of back axle can it be done by counting revolutions of propshaft to revolutions of wheel i have always thought it could for some reason but on trying it on our c 30 rear axle it doesnt to work out as the book states . thr front axle has had the diff removed and i want to replace it knowing it has to match the rear axle. and dont want to fit the wrong parts
thanks vic eaton .l