Need to know what rear

now since we know its a 489 case in a 8.75 housing now leave the jack under it and put jack stands under the body, then crawl under the vehicle and mark a horizontal line about two inches long on the driveshaft with a piece of chalk.

Mark the bottom of one of the rear tires at the 6 o'clock position with a piece of chalk.

Use the chalk mark on the rear tire as a reference and begin rotating the tire by hand from a position that allows you to see the driveshaft.

Turn the rear tire one complete revolution while simultaneously counting the number of revolutions of the driveshaft indicated by the horizontal chalk mark. Be as accurate as possible.

Determine your gear ratio, which is the number of driveshaft revolutions that were made in relation to one tire revolution. For instance, if your driveshaft rotated three and one half times in relation to one tire revolution, your gear ratio is 3.50.

Use the hydraulic jack to raise the vehicle high enough to remove the jack stands from under the axle housing.