Raise the vehicle and support it securely on jack stands. Place the transmission in Neutral with the parking brake off. Make reference marks on the driveshaft flange and the pinion flange in line with each other. If you're working on a1999 or later 2WD Pathfinder, also mark the front of the driveshaft to the transmission flange. Remove the rear universal joint nuts and bolts. If the vehicle has a two-piece driveshaft, unbolt the center support bearing from the cross member. Lower the rear of the driveshaft and slide the front of the driveshaft out of the transmission or transfer case. Wrap a plastic bag over the transmission or transfer case housing and hold it in place with a rubber band. Remove the plastic bag from the transmission or transfer case and wipe the area clean. Slide the front of the driveshaft into the transmission or transfer case or, if you're working on a 1999 or later 2WD Pathfinder, line up the match marks, install the bolts and tighten them to the torque. On models with a two-piece driveshaft, position the center support bearing on the cross member, install the fasteners and tighten them to the torque. Raise the rear of the driveshaft into position, checking to be sure the marks are in alignment. Install the bolts and nuts, tightening them to the torque. For 4WD models, mark the relationship of the driveshaft to the front differential companion flange and to the transfer case companion flange. Remove the bolts and nuts from the flanges, then lower the shaft from the vehicle. Attach the ends of the shaft to the differential and transfer case companion flanges, install the bolts and nuts and tighten them to the torque. Install the skid plate (if equipped).