SKF 25661 Automatic Transmission Seal - Rear

Automatic Transmission Seal for Allison Applications

SKF 25661 is an automatic transmission seal built for rear-position service in a range of heavy-duty truck and utility applications. With a polyacrylate sealing surface and precise dimensions, it is suited for transmission sealing where fluid retention and contamination control matter.

Compatible With Chevrolet Silverado 2500 HD, Silverado 3500, Silverado 3500 HD, GMC Sierra 2500 HD, Sierra 3500, Sierra 3500 HD, Hummer H1, and select Ford F-250 and F-350 Transmatic transmission applications. SKF 25661 is also a direct cross-reference for Monroe Shocks & Struts 172286 and 182286 for the same application.

Key Features

• Automatic transmission seal for rear installation
• Polyacrylate sealing surface type for transmission sealing service
• Outside diameter: 3.628 in.
• Shaft diameter: 2.563 in.
• Width: 0.469 in.
• SKF part number 25661

Detailed Description

SKF 25661 is engineered as a transmission seal for applications that require accurate fit and dependable sealing performance. SKF has a long history in seal design, and this part reflects that experience through application-specific dimensions and material selection. The polyacrylate sealing surface is used to help maintain a stable seal in transmission environments where heat, fluid exposure, and contamination are common concerns.

This seal is listed for rear-position use on 2001-2006 Chevrolet Silverado 2500 HD and Silverado 3500, 2001-2006 GMC Sierra 2500 HD and Sierra 3500, 2006 Hummer H1, 2007 Chevrolet Silverado 2500 HD Classic and Silverado 3500 Classic, 2007 GMC Sierra 2500 HD Classic and Sierra 3500 Classic, and 2007-2017 Chevrolet Silverado 3500 HD and GMC Sierra 3500 HD. It also fits 1957-1963 Ford F-250 and F-350 with Transmatic transmission applications.

What This Seal Helps Address

• Transmission fluid seepage at the rear seal area
• Contamination entering the transmission through a worn seal
• Leak-related fluid loss during normal operation
• Seal wear from age, heat, and fluid exposure
• Service replacement needs on Allison-equipped heavy-duty trucks

Installation Notes and Tips

Verify shaft diameter, outside diameter, and width before installation to confirm the seal matches the transmission case and shaft dimensions. Inspect the sealing surface and surrounding components for wear, scoring, or contamination before assembly. Clean the sealing area thoroughly and follow the transmission service procedure for the specific vehicle and transmission model.

For fitment-specific service, confirm the rear transmission application on Chevrolet Silverado 2500 HD, Silverado 3500 HD, GMC Sierra 2500 HD, and Sierra 3500 HD models before installation. The same verification applies to Ford F-250 and F-350 Transmatic applications listed for this part.

Quality Assurance

SKF manufactures seals to specific designs using premium materials and controlled production standards. The brand’s seal engineering background and long-term OE-style sealing focus support consistent fit and service life in demanding transmission applications.