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How to Determine the Final Gear Ratio in a BMW

A cars differential receives the torque force generated by the engine and transmission, via the driveshaft, and distributes it to the driven wheels. The differential uses gears to reduce the speed of the input force -- the engine spins at higher RPMs than the wheels. The difference between the input speed and the output speed is called the final gear ratio. Every BMW differential has the final gear ratio stamped on it, as well as a letter designating whether it is an open or limited-slip differential. Depending on the year and model of your BMW, the stamp may be on either side or the rear of the differential, typically found on a flat area adjacent to a bolt. Since BMWs are performance-oriented cars, it may be necessary to raise the rear of the vehicle in order to view the stamping.

Instructions

1

Raise the vehicle using a floor jack, and place it securely on jack stands if necessary.

2

Locate the differential between the two rear tires. Depending on the year and model, the stamp may be on the either side or on the rear of the differential. Look for a flat, smooth area next to a bolt, with a series of letters and numbers stamped on it.

3

Clean the stamping using a rag and wire brush, if necessary. Depending on the age and use of the vehicle, a significant amount of grime may have accumulated.

4

Decode the stamping. It will be comprised of eight characters. The first is a letter, most likely an N or R, which designates an open differential. The letter S signifies a limited-slip differential. After that will be three digits, such as 345. This indicates a final drive ratio of 3.45:1. After that will be four digits, such as 0722, which refer to the part number of the differential.

Posted by Unknown at 5:30 AM

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