National 340847 Automatic Transmission Manual Shaft Seal

Overview of National 340847 Automatic Transmission Manual Shaft Seal

The National 340847 automatic transmission manual shaft seal is engineered for reliable sealing performance in heavy-duty vehicles. Designed specifically for Chevrolet, GMC, and Hummer models, this oil seal helps maintain transmission integrity by preventing fluid leaks around the manual shaft.

• Inside diameter: 0.500 inch (12.7 mm)
• Outside diameter: 0.756 inch (19.2 mm)
• Thickness/width: 0.125 inch (3.18 mm)
• Sealing material: durable nitrile rubber
• Housing bore size: 0.750 inch (19.05 mm)
• Part number: 340847

Technical Details and Material Specifications

This National 340847 seal is constructed from nitrile, a material known for its resistance to oil, heat, and wear, making it suitable for transmission applications. The seal’s precise dimensions—0.500 inch inside diameter and 0.756 inch outside diameter—ensure a tight fit on the manual shaft and housing bore, minimizing the risk of leaks. With a thickness of 0.125 inch, the seal provides a robust barrier against contaminants while maintaining flexibility for shaft movement.

Compatible Vehicles and Applications

This automatic transmission manual shaft seal is compatible with a range of Chevrolet, GMC, and Hummer models, including:

• Chevrolet Silverado 2500 HD, 2500 HD Classic, 3500, 3500 Classic, and 3500 HD
• GMC Sierra 2500 HD, 2500 HD Classic, 3500, 3500 Classic, and 3500 HD
• Hummer H1

It is designed to replace worn or damaged seals in these vehicles’ automatic transmissions, helping to maintain proper fluid retention and transmission performance.

Common Issues Addressed by the National 340847 Seal

• Prevents transmission fluid leaks around the manual shaft
• Reduces contamination ingress that can damage transmission components
• Maintains proper hydraulic pressure within the transmission system
• Minimizes premature wear of transmission shafts and bearings
• Helps avoid costly transmission repairs due to seal failure

Installation Notes and Tips

• Ensure the shaft and housing bore are clean and free of debris before installation
• Lubricate the seal lip with transmission fluid or compatible lubricant to ease installation
• Use proper tools to press the seal evenly into the housing bore without distortion
• Verify correct orientation of the seal to ensure optimal sealing performance
• Inspect the shaft for wear or damage before installing the new seal

Quality Assurance and Warranty Information

National transmission seals are manufactured to meet industry standards for durability and performance. The 340847 seal undergoes rigorous quality control to ensure dimensional accuracy and material integrity. While specific warranty terms may vary, National typically offers coverage against manufacturing defects to provide confidence in the product’s reliability.