Once the hub and bearing unit wears down or breaks, you have to replace the entire unit because it doesn't come apart. To take off the parts, first release the cotter pin and reduce the driveaxle/hub nut on 4WD vehicles. First, loosen the wheel lug nuts. Raise the vehicle and place it safely on jackstands. Remove the wheel after that. First, take off the brake disc and wheel speed sensor from around the hub. Move the hub retaining bolts from the back of the knuckle. If you have the right tools, you can usually do this without taking out the driveaxle, although you may need to remove the entire driveaxle if you don't have the right tools. To finish, take off the disc shield and hub from the knuckle itself, and on 4WD vehicles, slide the assembly off the driveaxle splines. You need to clean up the matching areas of these components: the knuckle, bearing flange, and hole in the knuckle. Put the hub assembly with bearings into the knuckle and on 4WD driveaxle ends, applying multi-purpose grease on the spline connections before attaching them. Securely put the disc shield in place and screw in fresh bolts. Start by hooking up the wheel speed sensor, then put the brake disc on and its mounting plate, before adding the caliper. For vehicles with 4WD, first put the driveaxle/hub nut in place and tighten it, then put a new cotter pin in. By putting on the wheel, lowering the car, and making sure lug nuts are tight, you've finished the job.