National 5203 Automatic Transmission Extension Housing Seal Kit

Automatic Transmission Extension Housing Seal Kit

National 5203 is an automatic transmission extension housing seal kit built for Ford and Lincoln applications that use the 4R100, E4OD, C6, or FMX transmission families. It combines a nitrile oil seal with a matching bushing and uses a counter-clockwise spiral lip design for the specified shaft and housing dimensions.

Key Features

• National 5203 extension housing seal kit for automatic transmission service
• Contains 7300S seal and RP661 bushing
• Nitrile construction with Redi-Coat applied
• Counter-clockwise spiral lip design
• Housing bore: 2.500 in. / 63.500 mm
• Shaft size: 1.685 in. / 42.800 mm
• Outside diameter: 2.506 in. / 63.650 mm
• Flanged outside diameter: 2.850 in. / 72.390 mm
• Overall width with side lip: 1.250 in. / 31.750 mm

Detailed Description

National has supplied sealing solutions for more than 75 years, and part number 5203 reflects that focus with an oil seal kit engineered around the listed transmission and shaft dimensions. The nitrile seal material is paired with a bushing to support extension housing service on a wide range of Ford truck, van, and SUV applications, including Ford F-150, Ford F-250 Super Duty, Ford E-350 Super Duty, and Lincoln Navigator models listed in the fitment data. This part cross-references Quality-Built 16727 for the same application.

What It Is Used For

• Replacing a worn extension housing seal on automatic transmissions
• Addressing fluid leakage at the transmission tail housing
• Restoring sealing performance where the shaft and bushing interface has wear
• Servicing Ford E-150, F-150, and related truck or van drivetrains with the listed transmission types
• Supporting repair work on older Ford, Lincoln, and Mercury applications with C6, E4OD, FMX, or 4R100 transmissions

Installation Notes and Tips

Verify the transmission family, shaft diameter, housing bore, and seal orientation before installation. This kit is listed for applications with a 1.6850 in. shaft and includes bushings; notes in the fitment data specify use without boot on the 4R100 and E4OD applications. Clean the housing bore and shaft surface thoroughly, and confirm the counter-clockwise spiral lip design is oriented correctly during assembly.

Quality Assurance

National builds sealing products with long-term industry experience and ongoing design support for current and legacy vehicles. Part number 5203 is manufactured as a precision-fit oil seal kit for the specified dimensions and transmission applications.