National 2457 Automatic Transmission Extension Housing Seal

Automatic Transmission Extension Housing Seal

National 2457 is an automatic transmission extension housing seal built for heavy-duty GM applications that need a precise sealing surface at the transmission tail housing. It uses a polyacrylate sealing material with a counter-clockwise spiral lip design and Redicoat treatment to support consistent sealing performance in demanding driveline environments.

Use this seal when servicing GM trucks, vans, and SUVs such as Chevrolet Silverado 2500 HD, GMC Sierra 2500 HD, and Chevrolet Express 3500. National 2457 is sized for a 2.125-inch shaft and a 2.880-inch housing bore, with a 0.550-inch width for proper extension housing fitment.

Key Features

• Part number: 2457
• Automatic transmission extension housing seal / oil seal
• Polyacrylate construction for sealing durability
• Counter-clockwise spiral lip design
• Redicoat surface treatment
• Inside diameter: 2.125 in. (53.980 mm)
• Outside diameter: 2.885 in. (73.280 mm)
• Housing bore: 2.880 in. (73.150 mm)
• Width: 0.550 in. (13.970 mm)
• Flanged outside diameter: 3.150 in. (80.010 mm)

Detailed Description

National has supplied sealing solutions for more than 75 years, and this extension housing seal reflects that focus on dimensional accuracy and drivetrain sealing. The 2457 is a Type 74 oil seal in the 2000 series, engineered for automatic transmission extension housing service where the shaft and bore dimensions must match closely to control fluid retention and reduce leakage at the tail housing.

This part cross-references Febi-Bilstein 21111 and Gates 21236 for the same application. It is listed across a wide range of GM fitments, including 1991-2009 Chevrolet and GMC trucks, vans, and SUVs with over 15,000 lb GVW and without boot, plus 4L80-E transmission applications where noted. Search terms such as Chevrolet Express 2500 transmission extension housing seal, GMC Savana 3500 automatic transmission seal, and GMC Sierra 2500 HD extension housing seal all align with this part family.

What It Helps Address

• Transmission fluid seepage at the extension housing
• Worn or hardened tail housing seal material
• Leakage around the output shaft area
• Service replacement during transmission maintenance
• Seal wear on high-load GM truck and van applications

Installation Notes and Tips

Verify shaft diameter, housing bore, and seal width before installation. Clean the extension housing bore and inspect the shaft surface for scoring or wear before pressing in the new seal. Confirm the vehicle uses the listed over-15,000 lb GVW or 4L80-E configuration where required, since fitment varies by application notes. For best results, match the seal orientation to the transmission service procedure and avoid damaging the lip during installation.

Quality Assurance

National is recognized for premium sealing products and long-running OE-style sealing expertise. Part number 2457 is built to the listed dimensional specifications and material design for transmission service on covered Chevrolet and GMC applications.