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Precision-Engineered Traction for BMW M Platform: OS Giken Super Lock LSD BM237-HA
The OS Giken BM237-HA Super Lock LSD brings Japan's most refined limited slip differential technology to the BMW E36 Euro M3, E38, E39 M5, E46 M3, E60 M5/6, E8X M, and E9X M3. Built around OS Giken's patented pressure ring design with a spline-through-side-gear architecture, the OSGBM237-HA accommodates up to twice the friction plates of competing designs, delivering smooth, progressive 100% locking capability with a stock-like street character and full track-ready response. Every component is chemically heat treated, raw-forged, or precision machined from high-grade steel to meet the demands of high-horsepower S54 and S65 applications. When you replace an open differential with the OS Giken BM237-HA, you eliminate the most common limiting factor in putting BMW M power to the pavement.
Key Features
- Patented pressure ring design: spline-through-side-gear architecture allows up to 2x the friction plate count of competing LSDs for more progressive and consistent locking
- Chemical heat treatment on all components: maximum durability under sustained track-level thermal loading
- High-grade steel alloy construction throughout: superior material specification versus cast iron alternatives
- Raw-forged gears: maximum strength and fatigue resistance versus machined-from-billet gear sets
- Precision-machined clutch discs: both sides machined simultaneously to extremely tight tolerances, resulting in minimal warpage and consistent engagement
- Single-billet machined LSD case: no weld joints, uniform geometry, maximally consistent clutch engagement across all plates
- Progressive 100% lock capability: starts with low preload and locks completely under power for predictable, neutral handling
- Quiet operation: street-friendly character with full progressive lock under high load conditions
- Tunable preload and ramp angles: initial torque, lock progression timing, and ramp angles are all adjustable in-house for power and driver preference
- 210mm / 215mm housing compatibility: fits BMW's M-platform 210 and 215mm differentials as found in E36 Euro M3, E39 M5, and E46 M3
Fitment
| Year Range | Make | Model | Trim |
|---|---|---|---|
| 1994-1999 | BMW | M3 | E36 (Euro 3.2L S54 only) |
| 1996-2001 | BMW | 740i / 750iL | E38 |
| 1999-2003 | BMW | M5 | E39 |
| 2001-2006 | BMW | M3 | E46 |
| 2006-2010 | BMW | M5 / M6 | E60 / E63 |
| 2008-2013 | BMW | 1 Series M | E82 / E88 |
| 2008-2013 | BMW | M3 | E90 / E92 / E93 |
Specifications
| Detail | Value |
|---|---|
| Part Number (MPN) | BM237-HA |
| Brand | OS Giken |
| Type | Super Lock LSD (Clutch Type) |
| Ramps | 25/35 (1.5-way) |
| Lock Timing | 336 |
| Total Plates | 20 |
| Preload | 10S |
| Housing Size | 210mm / 215mm |
| Material | High-Grade Steel Alloy |
| Country of Manufacture | Japan |
| UPC | N/A |
What's Included
- OS Giken BM237-HA Super Lock LSD unit
- All internal friction discs, pressure rings, and hardware as assembled
About OS Giken
OS Giken is a Japanese precision manufacturer with decades of motorsport heritage in LSD, engine, and drivetrain development. The OSGBM237-HA represents OS Giken's commitment to producing limited slip differentials that perform equally well on the street and on circuit. Every OS Giken LSD is built to exacting tolerances in Japan and designed for direct fitment with no modification to the OEM differential housing.
Frequently Asked Questions
Does the OS Giken BM237-HA fit the E46 M3?Yes. The OSGBM237-HA is specifically designed for the 210mm and 215mm differential housing found in the BMW E46 M3. It is a direct replacement for the factory open or Motorsport differential and requires no modification to the housing or carrier.
Does the OS Giken BM237-HA fit the E9X M3 with the S65 V8?Yes. The OSGBM237-HA fits the E90, E92, and E93 M3 equipped with the S65 V8 engine. It is tuned at the 25/35 ramp angle with 20 total plates and a 10S preload configuration for M platform power levels.
What is the difference between the OS Giken Super Lock LSD and a standard helical or Torsen LSD?The OS Giken BM237-HA uses a clutch-type pressure ring design that locks progressively from low preload to full 100% lock under high load conditions. Helical and Torsen units are torque-sensitive but cannot reach 100% lock and degrade under power oversteer conditions. The OS Giken design provides both street smoothness and full motorsport locking capability in one unit.
Can the OSGBM237-HA be tuned for more aggressive locking on track?Yes. OS Giken offers in-house tuning services for the BM237-HA. Initial torque can be adjusted with thicker or thinner cone springs. Lock progression timing can be modified with stiffer or weaker pressure ring springs. Ramp angles can be changed by swapping the pressure ring and iron cross for more aggressive configurations. TCD spec discs can also be installed for increased oil cooling and smoother operation.
Does the OS Giken BM237-HA work with the E39 M5?Yes. The OSGBM237-HA is listed for the E39 M5 which uses the 210mm differential housing. It is a direct fitment replacement for the factory open or LSD differential in the E39 M5 and delivers the same progressive lock performance as in the E46 M3 application.
What oil should be used with the OS Giken BM237-HA?OS Giken recommends consulting the OEM service manual for your specific BMW application for differential fluid specification. Gear oil compatible with clutch-type limited slip differentials is required. Do not use limited slip additives that are formulated to reduce chatter in conventional clutch-pack units without confirming compatibility with OS Giken's pressure ring design.
Is the OS Giken BM237-HA a bolt-in installation?The OSGBM237-HA is designed for direct fitment into the OEM differential housing on compatible BMW M platform vehicles. OS Giken recommends referring to the OEM service manual for installation procedures. Professional installation by a qualified differential specialist is strongly recommended to ensure correct bearing preload, backlash settings, and torque specs.
Does the BM237-HA fit the E60 M5 and E63 M6?Yes. The OSGBM237-HA is listed for the E60 M5 and E60/E63 M6, which use the 215mm rear differential housing. The same 25/35 ramp, 20-plate, 10S preload spec applies across all listed BMW M platform fitments in the 210/215mm housing family.
Installation Notes
- Refer to the OEM BMW service manual for your specific chassis and differential removal procedure
- Drain and remove the differential from the vehicle following BMW-specified torque sequences
- Disassemble the differential housing and extract the open or existing LSD unit
- Install the OS Giken BM237-HA into the housing, following OS Giken's assembly specs for shim selection and bearing preload
- Verify ring gear backlash to OEM specification
- Fill with appropriate gear oil rated for clutch-type limited slip differentials
- Reinstall the differential into the vehicle and torque all fasteners to BMW specification
- Allow a short break-in period at varied load before sustained track use
WARNING: This product can expose you to chemicals including lead and phthalates, which are known to the State of California to cause cancer and reproductive harm. For more information go to www.P65Warnings.ca.gov.
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