How to do a solid axle swap
Things You'll Need
Raise the rear of the truck with the floor jack and support the truck with jack stands under the axle. Remove the tire/wheel assembly using the lug wrench. Remove the brake drum by pulling it off. Place the drain pan under the differential.
Remove all the 13 mm bolts around the differential cover using a socket. Pry the cover off using a screwdriver and allow all the gear oil to drain. Clean the differential cover while the oil is still draining. Use the gasket scraper to remove all the silicone from the cover. Wipe it with a rag.
Rotate the differential by turning the axle hub until the center pinion pin with the small 1/4-inch retaining bolt is facing down. Make sure that the pin will have room to fall out without hitting the housing. The pin must drop out as close to the housing as possible so you have room to reach inside the differential to extract the C-clip from the axle. If you turn the differential with the pin out, the differential or spider gears will fall out and pose a headache to reinstall if you are not experienced. Remove the small retaining screw using a socket.
Drop the differential pinion pin out from the bottom and place it on a clean cloth along with the retaining screw. Push the axle to be replaced in toward the differential by hand by pushing on the hub. Look
inside the differential and you can see the end of the axle, which was allowed to move in when the pin was removed. Pull the C-clip off the end of the axle and place it on the clean cloth.
Pull the axle out of the differential and away from the vehicle. Install the new axle into the housing. Hold the axle hub, gently lift the inside end of the axle shaft and maneuver it around until it slips into the differential. Push it in all the way. Get under the truck and insert the C-clip over the end of the axle. Pull the axle out as far as possible and the C-clip will move into a small area in the housing, preventing the C-clip from falling off.
Insert the pinion pin, with the hole for the retaining screw down and aligned so the screw can be inserted. Insert the retaining pin and tighten it with a wrench.
Place a thin bead of RTV around the mating side edge of the differential cover and allow it to set up for approximately 5 minutes or until it does not stick readily to your finger. Install the cover and tighten the bolts with a socket. Remove the filler plug on the passenger side front of the differential. Fill the differential with the gear oil until it just begins to backflow out of the plug. Quickly install the plug and tighten. Install the brake drum and tire.Source: ehow.com