The pinion seal in the front and rear axles of four wheel drive trucks and SUVs exists to keep oil in and contaminants out of the differential. It is designed to be replaceable in the course of normal maintenance without the need for removing and disassembling the axle.
Set the parking brake and climb under the truck. Make sure you have your tools and the new seal within reach.
Mark one of the caps on the u-joint with the paint marker where it sits in the differential yoke, and mark its corresponding side of the yoke. This will allow reassembly with the correct orientation to preserve driveshaft balance and prevent excessive vibration.
Remove the u-bolts or bolts and straps which retain the u-joint.
Pull the end of the driveshaft free of the yoke, being careful to not allow the u-joint caps to fall off. Use the pry bar to loosen the u-joint, if necessary. Allow the end of the driveshaft to hang out of the way.
Bolt the yoke tool to the yoke with the handle pointing left as you face the yoke.
Release the parking brake and roll the truck slightly until the handle of the yoke tool contacts the ground, then reset the brake.
Mark the differential housing, yoke and yoke retaining nut using the paint marker. Make the marks all in a line, because these are your reassembly reference points.
Loosen and remove the yoke retaining nut by turning it counterclockwise with the breaker bar and socket. Remove the yoke by tapping the back of it all around the circumference with the hammer.
Pull out the old seal with the seal puller, and drive the new one in place with the seal driver and hammer.
Replace the yoke on the pinion shaft, lining up the marks so the splines will match.
Replace the nut and tighten it to its original position with the breaker bar and socket, using the paint marks as a reference.
Reconnect the driveshaft to the yoke, using the paint mark on the u-joint as a reference. Replace the u-bolts or straps and bolts, and tighten.
Repeat steps two through twelve for the front differential.
