National 4638N Manual Transmission Input Shaft Seal

Manual Transmission Input Shaft Seal for NP4500

National 4638N is a manual transmission input shaft seal built for applications using New Process 4500 and 4500HD transmissions. It is specified with a polyacrylate sealing material, Redicoat protection, and OE-style dimensions for a precise housing and shaft fit.

Use this seal when servicing manual transmission leaks on Chevrolet Silverado, GMC Sierra, and Dodge Ram trucks with the listed transmission configurations. The National 4638N is engineered for consistent sealing performance in high-mileage drivetrains.

Key Features

• Manual transmission input shaft seal for New Process 4500 and 4500HD applications
• Polyacrylate sealing material for transmission fluid resistance
• Redicoat finish for added sealing surface protection
• Inside diameter: 1.375 in. / 34.930 mm
• Outside diameter: 1.989 in. / 50.520 mm
• Thickness: 0.192 in. / 4.880 mm
• Housing bore: 1.982 in. / 50.340 mm
• National 4638N part number for catalog and service lookup

Detailed Description

National 4638N is an oil seal designed for manual transmission input shaft service in vehicles equipped with the New Process 4500 and 4500HD transmissions. Its 1.375-inch shaft size, 1.989-inch outside diameter, and 0.192-inch width support accurate fitment in the transmission housing. National has supplied sealing solutions for more than 75 years, and this seal reflects that focus on dimensional accuracy and material selection. This part cross-references BBB Industries 13608 for the same application.

Common Repair Uses

• Transmission fluid leaking from the input shaft area
• Wet bellhousing or clutch contamination from seal seepage
• Seal wear from high-mileage manual transmission operation
• Service replacement during clutch or transmission maintenance
• Restoring proper sealing on NP4500 and NP4500HD units

Installation Notes and Tips

Confirm the transmission model before installation, since this seal is listed for New Process 4500 and 4500HD applications. Inspect the shaft surface and housing bore for wear, scoring, or contamination before pressing in the new seal. Clean the sealing area thoroughly and verify the seal orientation matches the transmission design.

Fits 1994-2005 Dodge Ram 2500, with New Process 4500HD Transmission. Fits 1994-2005 Dodge Ram 3500, with New Process 4500HD Transmission. Fits 1996-1998 Chevrolet C1500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 1996-1998 Chevrolet K1500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 1996-2000 Chevrolet C2500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 1996-2000 Chevrolet C3500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 1996-2000 Chevrolet C3500, with New Process 4500HD Transmission. Fits 1996-2000 Chevrolet K2500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 1996-2000 Chevrolet K3500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 1996-2000 Chevrolet K3500, with New Process 4500HD Transmission. Fits 1999-2004 Chevrolet Silverado 2500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 2002-2006 Chevrolet Silverado 1500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 2001-2006 Chevrolet Silverado 2500 HD, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 2001-2006 Chevrolet Silverado 2500 HD, with New Process 4500HD Transmission. Fits 2001-2006 Chevrolet Silverado 3500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 2001-2006 Chevrolet Silverado 3500, with New Process 4500HD Transmission. Fits 2007 Chevrolet Silverado 2500 HD Classic, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 2007 Chevrolet Silverado 2500 HD Classic, with New Process 4500HD Transmission. Fits 2007 Chevrolet Silverado 3500 Classic, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 2007 Chevrolet Silverado 3500 Classic, with New Process 4500HD Transmission. Fits 1996-1998 GMC C1500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 1996-2000 GMC C2500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 1996-2000 GMC C3500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 1996-2000 GMC C3500, with New Process 4500HD Transmission. Fits 1996-2000 GMC K1500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 1996-2000 GMC K2500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 1996-2000 GMC K3500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 1996-2000 GMC K3500, with New Process 4500HD Transmission. Fits 1996-1999 GMC P3500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 1999-2004 GMC Sierra 2500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 2002-2006 GMC Sierra 1500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 2001-2006 GMC Sierra 2500 HD, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 2001-2006 GMC Sierra 2500 HD, with New Process 4500HD Transmission. Fits 2001-2006 GMC Sierra 3500, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 2001-2006 GMC Sierra 3500, with New Process 4500HD Transmission. Fits 2007 GMC Sierra 2500 HD Classic, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 2007 GMC Sierra 2500 HD Classic, with New Process 4500HD Transmission. Fits 2007 GMC Sierra 3500 Classic, Manual Transmission Output Shaft Bearing compatible with New Process 4500 Transmission. Fits 2007 GMC Sierra 3500 Classic, with New Process 4500HD Transmission.

Quality Assurance

National has focused on premium sealing solutions for more than 75 years, with product development aligned to current vehicle service needs. National 4638N is built to OE-style dimensional standards for transmission sealing service.