National 3404 Automatic Transmission Oil Pump Seal - Front

Automatic Transmission Oil Pump Seal for Ford Applications

National 3404 is an automatic transmission oil pump seal built for Ford front-position applications that call for a precise sealing fit. It uses silicone sealing material and a clockwise-spiral lip design to help maintain sealing performance in demanding transmission service.

With dimensions of 1.996 in. inside diameter, 2.751 in. outside diameter, and 0.325 in. width, this seal is sized for the specified housing bore and shaft measurements. National’s 3000 series sealing design reflects the brand’s long history in premium sealing solutions for transmission repair.

Key Features

• Part number: 3404
• Automatic transmission oil pump seal
• Silicone sealing material
• Clockwise-spiral lip design
• Inside diameter: 1.996 in. / 50.700 mm
• Outside diameter: 2.751 in. / 69.880 mm
• Width: 0.325 in. / 8.260 mm
• Flanged outside diameter: 3.020 in. / 76.710 mm
• Series 3000, Type 75

Detailed Description

National 3404 is an oil seal for the transmission pump area, engineered around the listed shaft and housing bore dimensions for a proper service replacement. The silicone sealing material is paired with a spiral lip profile to support consistent contact at the sealing surface. This part cross-references ATP FO-191 and LO-29 for the same application.

It is a direct-fit service part for many Ford, Lincoln, and Mercury rear-wheel-drive and truck-based platforms, including Ford F-150, Ford E-150, and Ford Crown Victoria applications with the specified transmissions. National has supplied sealing products for more than 75 years and continues to update its designs for modern vehicle service needs.

What It Helps Address

• Transmission fluid leakage at the oil pump seal area
• Sealing wear from age, heat, and fluid exposure
• Poor sealing after transmission service or rebuild
• Fluid loss that can affect transmission operation
• Fitment issues when replacing a worn pump seal on Ford 4R70E, 4R75E, 4R100, E4OD, or AOD-E family transmissions

Installation Notes and Tips

Verify the shaft diameter, housing bore, and transmission family before installation. Clean the pump bore and sealing surface thoroughly, and inspect the shaft for scoring or wear that could shorten seal life. Confirm the front-position application and match the seal to the exact transmission listed for your vehicle, such as Ford F-150, Ford E-150, or Lincoln Town Car service.

For best results, install the seal squarely to avoid lip distortion and check that the sealing edge is fully seated before reassembly.

Quality Assurance

National is known for premium sealing solutions and has supported the automotive aftermarket for more than 75 years. Part 3404 is built to the brand’s established sealing standards for transmission service.