Extensive testing was performed on both the ring-gear and hypoid-gear churning used to move the oil in the axle bowl to lubricate tandem axles. The gear pump test results were used to establish the pump characteristics, as well as the volumetric and mechanical efficiencies. The churning test results were used to formulate an empirical model used in an analysis to predict the energy loss. All testing was done with SAE 90W and 140W lubricants. The results from these experiments, along with some analytical formulations, were used and incorporated into a computer program. The results of the component testing showed that the hypoid-gear churning loss is a large energy loss, amounting to as much as 1.5 horsepower per axle. Since the energy losses in the gear pump amounted to only 0.2 horsepower, around a one horsepower savings per axle is achievable by lubricating the entire axle with the gear pump.