3.55 Ratio 8.75in Mopar 489 Case

The 3.55 Ratio 8.75in Mopar 489 Case by Richmond represents a purpose-built differential assembly for Mopar enthusiasts and performance-oriented mechanics seeking superior gear ratio tuning on classic and modern Chrysler platforms. This complete carrier case assembly allows builders to dial in precise final drive characteristics without sourcing multiple component parts individually. Whether you're restoring a muscle car, upgrading a daily driver, or building a street-strip hybrid, this 3.55 ratio configuration delivers the ideal balance between acceleration response and highway cruising capability for mid-range performance applications.

The Richmond 489 case is engineered to OEM specifications and accepts standard Mopar ring-and-pinion sets, ensuring bolt-in compatibility with existing driveshaft assemblies and brake components. The 3.55 gear ratio sits at a practical sweet spot—lower than stock 2.76 or 3.23 ratios for improved acceleration off the line, yet taller than aggressive 3.73 or 4.10 ratios that compromise fuel economy and highway manners. The compact 8.75-inch diameter case design fits original equipment locations while maintaining structural integrity under sustained load; weighing just 15.8 lbs, this assembly integrates seamlessly into weight-sensitive restorations and performance builds. All bearing surfaces and casting quality meet Richmond's manufacturing standards, backed by decades of differential expertise.

Installation suits DIY builders with intermediate suspension knowledge and professional shops performing comprehensive drivetrain service or upgrades on B-body, E-body, and A-body Mopar platforms. This case pairs flawlessly with OEM-spec pinion bearings, carrier bearings, and axle shafts—no fabrication or modification required. Mechanics upgrading from factory 8.75-inch rear axles benefit from the straightforward bolt-in design and the proven 3.55 ratio's responsiveness on street applications, weekend cruise events, and light drag strip duty. Verify your vehicle's original case identification and axle width before ordering to ensure correct fitment.