The extension housing seal (located in the tail section of the transmission assembly) controls oil leakage around the driveshaft. Continued failure of this seal usually indicates a worn output shaft bushing. If so, there will be signs of the same wear on the driveshaft, at the point where it contacts the seal and bushing. The seal is a fairly simple component to install, but it requires the proper driver tool to assure proper installation and prevent the danger of component damage.
- Raise and support the rear of the truck safely using jackstands. If the rear of the vehicle is supported sufficiently, transmission oil loss will be minimized during the procedure. Keep a drain pan handy though, just to be sure.
- Matchmark and remove the driveshaft from the truck. Refer to the procedure later in this section for details.
- Pry the seal out of the transmission extension housing. Be careful not to score and damage the housing sealing surface when removing the seal.
- Coat the outside of the replacement seal using a suitable locking compound.
- Fill between the seal lips with chassis grease and drive the seal into position using J-21426, or an equivalent seal installation tool.
- Align and install the driveshaft.
- Lower the rear of the truck or raise and support the front as well so the vehicle is level, then check the transmission fluid and add, as necessary. Remove the jackstands and carefully lower the vehicle.