Subaru OEM 3.9 Rear Ring & Pinion Subaru STI 2004-2005 | 38104AA260

Overview

The Genuine Subaru OEM 3.9 Rear Ring & Pinion (Part #38104AA260) is a factory-original differential gear set designed specifically for the 2004–2005 Subaru Impreza WRX STI. Engineered to Subaru's exacting tolerances, this ring and pinion delivers the precise 3.909 final drive ratio that defines the STI's legendary rear differential performance. Whether you're rebuilding a worn rear differential or restoring factory drivetrain specifications, this OEM gear set ensures an exact fit with zero compromise.

Key Features & Benefits

• Genuine Subaru OEM Quality – Manufactured to factory specifications, ensuring the same precision fit and long-term durability as the original components that came in your STI from the factory.
• Exact 3.909 Final Drive Ratio – Maintains the factory-correct rear gear ratio for optimal power delivery, throttle response, and AWD system balance specific to the 2004–2005 STI drivetrain.
• Precision-Machined Gear Teeth – Factory gear-cutting and heat-treatment processes provide smooth engagement, minimal noise, and resistance to wear under high-performance driving conditions.
• Perfect OEM Fitment – Designed as a direct replacement with no modifications required; eliminates the guesswork and risk associated with aftermarket or incorrect-ratio gear sets.
• Backed by Subaru's Parts Warranty – Genuine Subaru parts are supported by the Subaru OEM parts warranty for added peace of mind.
• Preserves AWD System Integrity – Using the correct OEM ring and pinion ensures the front-to-rear torque split and DCCD system operate as engineered by Subaru.

What's Included

• 1x Genuine Subaru OEM Rear Ring Gear
• 1x Genuine Subaru OEM Rear Pinion Gear

Specifications

Fitment & Compatibility

This ring and pinion is a direct OEM replacement for the following vehicles:

Always verify your Subaru part number against your vehicle's VIN and current differential ratio before ordering. Cross-reference part number 38104AA260 to confirm compatibility with your specific build.

Installation

Ring and pinion replacement requires professional-level mechanical skill and specialized tools including a bearing press, dial indicator, and pattern compound for proper gear mesh and backlash setup. This is not a bolt-on installation — professional installation by a qualified Subaru technician or experienced drivetrain specialist is strongly recommended to ensure correct preload settings and long-term reliability.