National 470774 Automatic Transmission Extension Housing Seal

Automatic Transmission Extension Housing Seal for Buick and Cadillac

National 470774 is an automatic transmission extension housing seal built for select Buick and Cadillac applications with GMC DynaFlow and GMC Flight-Pitch transmissions. It uses nitrile construction with Redi-Coat treatment to support a reliable seal at the transmission tail housing, helping maintain fluid control in older driveline assemblies.

• Automatic transmission extension housing seal for transmission tail housing service
• Nitrile material for sealing performance in transmission fluid environments
• Redi-Coat finish for improved sealing surface preparation
• Inside diameter: 1.375 in. / 34.930 mm
• Outside diameter: 2.066 in. / 52.480 mm
• Housing bore: 2.062 in. / 52.370 mm
• Thickness/width: 0.375 in. / 9.530 mm
• Zero duplication part in the National 470000 series

Detailed Application Coverage

National 470774 is an oil seal for transmission extension housing service on classic Buick and Cadillac models. It is listed for 1950-1958 Buick Roadmaster with GMC DynaFlow Transmission, 1954-1958 Buick Century with GMC DynaFlow Transmission, 1958 Buick Century with GMC Flight-Pitch Transmission, 1957-1958 Buick Roadmaster with GMC Flight-Pitch Transmission, 1954 Buick Skylark with GMC DynaFlow Transmission, 1959-1960 Buick LeSabre with GMC DynaFlow Transmission, and 1953 Cadillac DeVille with GMC DynaFlow Transmission; 3 Speed. This part cross-references Dorman - HELP 13585 and FEL-PRO 60451 for the same application. National 470774 is a direct-fit service seal for these transmission configurations when the housing bore and shaft dimensions match the listed specifications.

What This Seal Helps Address

• Transmission fluid seepage at the extension housing
• Leakage around the output shaft area
• Seal wear from age, heat, and fluid exposure
• Service replacement for deteriorated tail housing seals
• Fitment-specific repair on Buick Roadmaster, Buick Century, Buick LeSabre, Buick Skylark, and Cadillac DeVille applications

Installation Notes and Tips

Verify the housing bore, shaft diameter, and seal width before installation. Clean the extension housing bore thoroughly and inspect the shaft surface for scoring or wear that could affect sealing. Use proper seal installation tools to keep the seal square in the bore and avoid damaging the nitrile lip during assembly.

Quality Assurance

National has supplied sealing solutions for more than 75 years and continues to develop parts for older and current vehicle platforms. Part number 470774 is built to the listed dimensional specifications for service use in the confirmed Buick and Cadillac transmission applications.