Automatic transmissions have two important seals, one in the back to seal the driveshaft yoke and one in the front that seals the torque converter. Manual transmissions also use a driveshaft seal. Although the driveshaft seal is the easier of the two seals to replace, the procedure requires you to remove the driveshaft. The front seal, located behind the torque converter, requires you to remove the transmission -- a more complicated process. Always replace the front seal when replacing the transmission.
Spot two wheel blocks, one on the front side of each front tire, with the vehicle parked on a solid level surface. Do not apply the emergency brake.
Place a jack under the rear differential, and lift the rear of the vehicle off the ground. Insert two jack stands, one under each axle tube as close to the wheel as possible.
Turn the key just far enough to unlock the ignition, and place the gearshift in neutral. Do not crank the engine over.
Use a wrench to loosen and remove the U-bolts or universal clips that hold the rear of the driveshaft to the differential. Use a large screwdriver to pry the driveshaft forward and free it. Wrap duct tape around the universal caps to prevent them from falling off the driveshaft.
Place adrain pan under the tail of the transmission, and carefully slide the driveshaft out of the tail of the transmission.
Tap a small thin-blade straight screwdriver into the flat tin cover of the rear seal with a hammer, and pry it out of the transmission tail. Wipe the transmission tail shaft clean of oil with a rag.
Place the new seal, with the flat tin surface facing the rear of the vehicle, into the transmission tail shaft. Place a small block of wood flat over the seal, and tap the wood block with your hammer to start the seal into the transmission tail shaft. Check to ensure the seal fits squarely into the transmission. Again, place the flat side of the wood block against the seal and continue tapping the block until the transmission seal seats tightly against the transmission tail shaft.
Slide the driveshaft nose back into the transmission seal. Take care not to damage the new seal when sliding the driveshaft back in.
Replace the U-bolts or universal clips that attach the rear of the driveshaft to the rear differential, and tighten them.
Use the jack to raise the rear of the vehicle from the jack stands, remove the jack stands and place the vehicle back on the ground.
