Ductile iron has traditionally been the material of choice for differential housings on rear wheel drive axles because of it's durability and low cost. There is a trend to use Aluminum as a differential housing material to reduce vehicle weight and improve fuel economy. One must be careful to account for the differences in material properties of the two materials when switching to Aluminum. Careful consideration of bearing fitting practice, pre-load setting procedure, and in some cases, design to achieve optimum axle performance is necessary. This paper is written as a bearing guide for differentials with Aluminum housings.