A method of simulating a split .mu. axle test for limited slip differentials for automotive applications. The method includes treating a clutch pack for a limited slip differential in a lubricant composition for a first period of time at a predetermined temperature. The clutch pack is mounted in a friction testing rig. A predetermined amount of test fluid is provided to the testing rig. A drive for the testing rig is cycled on and off for a predetermined number of on and off cycles. When the drive is on, a predetermined relative rotational speed between friction plates and metal plates in the clutch pack is generated.