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Differential gears are how power is transmitted to your wheels. The ring gear and pinion gear each have a specific amount of teeth on them. Those teeth translate into a gear ratio. The lower the gear ratio (numerically higher), the quicker the car accelerates. The taller the gear ratio (numerically lower), the slower the car accelerates. As an example, a 3.42 gear set allows the car to accelerate quicker than a 3.08 gear set. The gear ratio can be calculated by dividing the ring gear teeth by the pinion teeth. Factory gears always have both tooth counts stamped into the gears. A 3.23 gear set is a 42 tooth ring gear and a 13 tooth pinion, and are stamped 42-13. Gear sets are always matched. You cannot use a different pinion with a different gear set, nor can you use a different tooth count pinion or ring gear with a different ring gear or pinion.

Ring and pinions always need to be changed in sets, meaning if you damage a pinion gear, you also need to change the ring gear due to machining methods. Ring gears have no bearings on them, as they are bolted directly to the carrier. The bolts are REVERSE THREAD, which means you need to set your tool to "tighten" to remove the bolts, and "loosen" to tighten the bolts. They are reverse thread due to the direction the gear rotates, and to prevent the bolts from loosening on thier own. Pinion gears have one bearing pressed on them. Those bearings are specific to the race in the differential housing, so whenever you change a pinion gear, you should either transfer your original bearing over to the replacement pinion (as long as it's in good shape), or install a new pinion bearing on the pinion and a new race in the housing. A new crush sleeve should always be installed when changing a pinion gear.

Ring and pinion sets are specific to the differential, and are measured by the outside diameter of the ring gear. Generally speaking, the strength of a rear end is determined by the ring gear diameter. As an example, a 8 1/2" ring gear is stronger than a 7 1/2" ring gear. Generally speaking, the higher the pinion tooth count, the stronger the gear set, this is because there is a greater contact patch with higher tooth count gears.

Now the trick stuff... All gears have "backlash". Backlash is basically the "gap" before the gears mesh. A simple analogy for backlash would be a house door knob. When you turn the knob, there is a brief segment of rotation before it actually allows you to open the door. Backlash is measured with a tool called a dial indicator. Too little backlash or too much backlash, and the rear end will make a howling noise, or cause damage to the gears down the line. Backlash is adjusted by installing shims between the axle housing and the carrier. Installing shims on the driver side reduces backlash, installing shims on the passenger side increases backlash. Always consult the factory service manual to see the proper backlash adjustment. Achieving the proper backlash is sometimes time consuming, but essential for proper tooth engagement and gear life.

Changing differential gears is not for everyone, and should be installed by a qualified and experienced mechanic. Not to mention, there are a lot of specialty tools required as well.