How to Change a Transmission Sealby Don Bowman
The transmission seal that is most commonly replaced to prevent leakage is the tail shaft seal. This seals the driveshaft where it attaches to the output shaft of the transmission. It is attached at this point with the use of splines. As the vehicle moves, the driveshaft moves in and out as bumps are encountered. The seal keeps the fluid in the transmission when the driveshaft moves in and out.
Raise and support the vehicle on jack stands. Place the vehicle in neutral.
Unbolt and remove the driveshaft universal c-clamps at the pinion.
Place a container under the tail shaft to catch lost fluid. Pull the driveshaft out of the transmission.
Remove the seal with the use of the seal remover. If you do not have a seal remover, you can use a common screwdriver to pry the seal out. Take care not to scratch the surface of the transmission where the seal rides, else you will have a leak that cannot be fixed without replacing the tail shaft.
Press the new tail housing seal in as far as possible, making sure it is perfectly straight. To get it the rest of the way in, tap it around the edges with the hammer. Push the driveshaft into the tail housing, then hold the other end of the driveshaft up with the the c-clamps at the pinion, and tighten the clamps.