I also didn't spin the tires, believe it or not.Drive for no more than 30 minutes and let it cool for 1 hour. Do this for the first 100 miles (I know, I know). The racers will tell you they never break them in but, just do it and you wont have any problems. There is lots of friction as the gears seat themselves and that creates tons of heat. After 500 miles change the diff oil and don't forget the posi additive if it's a posi-traction.