The pinion seal on the 2002 Ford F150 is the main seal that prevents the gear oil from leaking our of the rear end. The pinion seal is seated inside the front of the rear end. The yoke that is inside of the pinion seal is attached to the rear end. The rear end yoke is also attached to the back side of the drive shaft. The pinion seal is designed to prevent any oil from leaking around the seal while the driveshaft is turning the rear end yoke. Replace the pinion seal immediately at the first sign of leakage.
Park the 2002 Ford F150 on a level surface and set the parking brake. Turn the engine off. Position the wheel chocks in the front of the rear wheels and behind the rear wheels.
Slide under the rear of the truck and locate the yoke on the front of the rear end that is attached to the yoke on the back side of the drive shaft. Mark the top of the rear end yoke and the top of the drive shaft yoke with a piece of chalk. This is so you can reinstall the drive shaft in the same direction that it came out.
Loosen and remove the U-joint strap bolts from the straps that connect the two yokes together with a ratchet and a socket. Place the bolts and straps in a safe area. Pull back on the drive shaft until there is enough room to lower the back side of the drive shaft to the ground. Use the rubber mallet if needed to tap the end of the drive shaft out of the rear end yoke. Place a rag or plastic bag around the U-joint caps and tape it with masking tape to prevent the caps from getting dirty or falling off of the U-joint.
Loosen the large nut that secures the rear end yoke to the rear end with an air impact ratchet and an air impact wrench socket. Turn the nut counterclockwise with the air ratchet until the nut loosens enough to unscrew it from the yoke shaft. Remove the nut and pull the rear end yoke out of the rear end. Use the rubber mallet if necessary to tap the yoke out of the rear end. Place the yoke on the ground.
Slide the flat tip of the flathead screwdriver between the pinion seal and the rear end housing. Use the rubber mallet if necessary to tap the screwdriver between the seal and the housing. Pry the seal outward in different locations around the housing until it comes out of the rear end. Discard the old seal.
Wipe away any oil, dirt or debris from around the pinion seal seat with a clean rag. Place the new pinion seal into the front of the rear end. Make sure that the entire seal is inside of the pinion seal seat. Place the pinion seal driver squarely over the front of the pinion seal. Make sure that the front of the driver is flush all the way around the front of the seal. Hold the pinion seal driver level with one hand. Tap the end of the driver with the rubber mallet with the other hand until the seal is flush with the rear end facing.
Inspect the new pinion seal to ensure that it is completely flush with the rear end facing all the way around the seal. Push the rear end yoke back onto the rear end shaft and through the center of the new pinion seal. Screw the large nut onto the threads of the shaft and tighten the nut down until it stops tuning with the air ratchet and socket.
Reattach the back side of the drive shaft yoke to the rear end yoke with the straps and the strap bolts. Make sure to install both yokes together with the chalk marks lining up with each other. Tighten the strap bolts with the ratchet and a socket. Torque the strap bolts to 25 to 30 foot-pounds with a torque wrench and a socket.
Loosen and remove the differential gear oil fill plug with the square drive of a 3/8-inch ratchet. The fill plug is the plug near the center of the rear end. Turn the fill plug counterclockwise to remove.
Insert the hose on the fluid pump into the fill plug hole. Pump the 75/90 synthetic gear oil into the fill plug hole until the fluid begins to drip out of the fill hole. Once the fluid begins the drip out, the rear end will be filled.
Remove the hose and screw the fill plug back into the rear end.
Drive the 2002 Ford F-150 around for about 10 minutes. Park the truck and recheck the pinion seal and the fill plug for any leaks.
