Mazda RX7 FD (FD3S) Rebuilt Rear Diff – Rare 3.9 Spirit R Ratio
Description
Mazda RX7 FD (FD3S) Rebuilt Rear Diff – Rare 3.9 Spirit R Ratio
Suits: Mazda RX7 FD (FD3S) Ratio: 3.9 (Rare Spirit R Factory Ratio) Carrier Type: Factory Helical / Torsen Style LSD Upgrade: Solid Pinion Bearing Spacer Upgrade
Upgrade your FD RX7 with this fully rebuilt rear differential featuring the rare 3.9 ratio from the Spirit R model. This ratio offers an excellent balance between acceleration and highway drivability, making it highly sought after among rotary enthusiasts.
This unit retains the factory helical (Torsen-style) LSD, providing smooth, progressive torque transfer without the harsh engagement of clutch-type LSDs.
Key Features:
Complete Rebuild: Fully stripped, inspected, and rebuilt using all new high-quality bearings and genuine Mazda seals.
Rare 3.9 Spirit R Ratio: Hard-to-find factory gearing offering good acceleration while maintaining comfortable cruising RPM.
Factory Helical / Torsen LSD: Smooth torque biasing differential for predictable handling and excellent street performance.
Solid Pinion Bearing Spacer Upgrade: Replaces the factory crush sleeve for improved strength, durability, and consistent preload under high load.
Refinished Housing: Comes with vapour blasted rear cover and gold zinc plated bolts for a clean OEM+ finish.
This is the ideal option for:
Spirit R style builds
Street-driven FD RX7s
Mild to high power 13B turbo setups
Drivers wanting smooth LSD operation without clutch chatter
Professionally assembled and ready to install.