After adding the gear oil and friction modifier, Custom Diff recommends that the axle be tilted in each direction for about 20 minutes. This ensures that the wheel bearings are adequately lubed. When it comes to axle break-in, heat is the enemy. For this reason, Custom Diff recommends five short trips of up to 10 miles with hour-long cooling breaks between each run. After that, they recommend keeping trips under 50 miles for the first 500 miles.