InMotion WS8181NA Differential Pinion Seal - Rear or Rear Outer

InMotion WS8181NA Differential Pinion Seal

The InMotion WS8181NA differential pinion seal is built with nitrile material to create a secure barrier at the pinion area and help keep contaminants out of the differential. It is a direct-fit sealing component for select Ford and Mercury rear axle applications, including Mustang, Cougar, Pinto, Bobcat, Monarch, Montego, Capri, and Villager models.

Key Features

• Nitrile construction for dependable sealing performance
• Inside diameter: 1.812 in.
• Outside diameter: 2.627 in.
• Thickness: 0.455 in.
• Shaft diameter: 1.812 in.
• Housing bore: 2.623 in.
• Fits rear and rear outer differential pinion applications
• Part number: WS8181NA

Fitment Details

• Fits 1975-1978 Ford Pinto, rear, with 8in ring gear.
• Fits 1971-1974 Ford Pinto, rear outer, with 6.75in ring gear.
• Fits 1964-1973 Ford Mustang, rear, with 8in ring gear.
• Fits 1967-1972 Mercury Cougar, rear, with 8in ring gear.
• Fits 1975-1978 Mercury Bobcat, rear, with 8in ring gear.
• Fits 1975-1978 Mercury Monarch, rear, with 8in ring gear.
• Fits 1974 Mercury Montego, rear, with 8in ring gear.
• Fits 1971 Mercury Montego, rear, with 8in ring gear.
• Fits 1972-1973 Mercury Montego, rear, with Ford axle.
• Fits 1968-1970 Mercury Montego, rear, with Ford axle.
• Fits 1967 Mercury Capri, rear, with 8in ring gear.
• Fits 1966-1967 Mercury Villager, rear, with Ford axle.
• Fits 1966 Mercury Capri, rear, with Ford axle.
• Fits 1962-1965 Mercury Villager, rear outer, with 7.25in ring gear.

Detailed Description

WS8181NA is a differential pinion seal engineered for select Ford and Mercury rear axle assemblies. Its nitrile sealing material helps maintain a tight interface at the pinion opening, reducing the chance of gear oil leakage while limiting the entry of dirt and moisture into the differential. This makes it a practical replacement for service work on classic Mustang, Cougar, Pinto, and Mercury rear axle setups where correct seal dimensions matter.

This part cross-references Monroe Shocks & Struts (e.g., 172286, 182286) for the same application. For buyers searching by application, this seal is a strong match for Ford Mustang rear differential pinion seal replacement, Mercury Cougar rear pinion seal service, and Ford Pinto rear outer seal applications with the listed ring gear and axle configurations. The part number WS8181NA is also useful when verifying the correct seal against existing service records or removed components.

Common Issues This Seal Can Address

• Gear oil seepage at the differential pinion area
• Contamination entering the differential housing
• Wear-related sealing loss on older rear axle assemblies
• Moisture intrusion around the pinion opening
• Service replacement for deteriorated or hardened original seals

Installation Notes and Tips

Confirm the axle configuration, ring gear size, and pinion seal dimensions before installation. Clean the housing bore and shaft area thoroughly, and inspect the pinion surface for wear or scoring that could affect sealing. Proper alignment during installation is important to avoid damaging the nitrile sealing lip and to help the seal seat evenly in the housing.

Quality Assurance

InMotion manufactures this seal with precision-focused construction and high-quality materials to support reliable differential sealing performance. The WS8181NA is specified for the listed Ford and Mercury applications and is built to help maintain a secure seal in rear axle service.