OS Giken BM237-HA Super Lock LSD for BMW E46/E9X M3, E34/E39 M5, Z4 M

Vehicle Fitment

• 1991-1995 BMW M5 (E34) Sedan
• 1999-2003 BMW M5 (E39) Sedan
• 2001-2006 BMW M3 (E46) Coupe and Convertible
• 2006-2008 BMW Z4 M (E85) Roadster and M Coupe
• 2008-2013 BMW M3 (E90/E92/E93) Sedan, Coupe, and Convertible

Fitment Notes

• Fits the shared differential housing used across these BMW M models - verify your specific differential type/ratio before ordering
• Professional installation is strongly recommended
• Applicable engines include S38 (E34 M5), S62 (E39 M5), and S54 (E46 M3, Z4 M); E9X M3 (S65) uses the same differential housing despite the different engine

Features

• Patented pressure ring design for smooth, progressive, and quiet locking behavior
• Spline-through-side-gear design allowing fitment of up to 28 friction plates - up to 2x more than competing designs
• True 100% progressive lock capability for consistent power delivery under load
• Standard spec allows low preload while retaining full progressive lock - feels close to an open differential at low speed, locks fully under load
• LSD case machined from a single billet piece for consistent uniformity
• Relief cut-out in the LSD case for the cone spring, reducing spring degradation and improving long-term durability
• Adjustable lock progression timing via optional stiffer/weaker pressure ring springs
• Customizable ramp angles by swapping the pressure ring and iron cross
• No break-in period or rebuild required due to precision manufacturing and high-grade materials

Specifications

• Differential type: Clutch-type limited slip, Super Lock design
• Friction plate capacity: Up to 28 plates
• Lock capability: 100% progressive lock
• Case construction: Single-piece billet
• Break-in required: None

Included Components

• 1x OS Giken Super Lock LSD Unit (BM237-HA)

Product Description

The OS Giken BM237-HA Super Lock LSD is a clutch-type limited slip differential built around the shared differential housing used across several of BMW's most iconic M models - the E34 M5, E39 M5, E46 M3, Z4 M, and E9X M3. Developed over more than four years, OS Giken's Super Lock design uses a spline-through-side-gear architecture that allows for up to 28 friction plates, roughly double the capacity of many competing LSDs, enabling genuine 100% progressive lock without the harshness that often comes with fully locking differentials.

A patented pressure ring design delivers smooth, quiet locking behavior that feels nearly like an open differential during low-speed driving, while still transmitting maximum power to the drive wheels under load. The single-piece billet case construction ensures consistent uniformity, and a relief cut-out for the cone spring reduces spring degradation over time. Lock progression timing can be further tuned using stiffer or weaker pressure ring springs, and ramp angles can be customized by swapping the pressure ring and iron cross - giving owners real flexibility to match the differential's behavior to their driving style.

This LSD is a significant upgrade over the factory M Dynamic limited slip system, which OS Giken and several tuning shops note is designed primarily as a street differential rather than one built for racing. It suits owners of the covered BMW M models who want genuine, race-proven traction - from club racers running E46 or E9X M3s to owners of classic E34 or E39 M5s looking to modernize their drivetrain. No break-in period or rebuild is required thanks to the precision manufacturing and material quality, and professional installation is recommended given the complexity of differential work.