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In rear-wheel drive automobiles the central drive shaft (or prop shaft) engages the differential through a hypoid gear(ring and pinion). The ring gear is mounted on the carrier of the planetary chain that forms the differential. This hypoid gear is a bevel gear that changes the direction of the drive rotation.
1 If your differential has been removed so that you can see and count the teeth on the gears, you can divide the number of teeth on the ring gear by the number of teeth on the pinion gear to come up with their ratio. 2  For example, 41/10 gives you a 4.10:1 gear ratio (the most common stock ratio).