The housing contains the output shaft, and most often, the vehicle speed sensor. The extension housing bushing is press-fit into the housing. Then the extension housing seal is installed to contain the transmission's fluid. The extension housing is sometimes called the tail housing.

Oil seals are used to protect shafts and bearings from ingress of dirt and foreign matter and egress of oil or grease. An oil seal generally consists of an outer circular metal part and an inner flexible member that does the actual sealing and is bonded to the metal part by chemical adhesive agents.