The gear side. You have to take it completely apart, set up the pinion bearing preload with no seal in it and when you get the preload set take the yoke back off and install the seal then re-assemble the front end and torque the pinion nut. Then re-install the carrier and set the backlash. To do this you'll need basic hand tools, a rotating inch lb. torque wrench, a large ft. lb torque wrench, a dial indicator setup and something to hold the yoke while you torque it to 220 ft. lbs. Unfortunately 489's are the worst since they use the crush sleeve.