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E39 M5 Differential Upgrade - Custom Options

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A custom differential is one of the best, and smartest, upgrades to have done to your E39 M5. Not only can you get more performance but you can also address the weak points in the M Variable limited slip diff. It's easy to forget about the rear axle when you're considering performance upgrades but changing the gearing is in the top 3 things to do to make the car faster. A custom diff is also a rebuilt unit with new seals, bearings, and limited slip unit.

Gearing The E39 M5 diff comes with a 3.15 gear ratio and relies on the torque of the motor for acceleration. But if you would like to get up into the torque curve sooner, this is your best bet. Which ratio you choose depends mainly on what your priorities are. If you use the car mostly for highway cruising the shorter ratios will result in higher RPM and worse fuel mileage. But the shorter ratios are better for around town driving where you want to be up into the torque curve more. Use the chart below for examples of the differences.

2002 E39 M5, 275/35-18" rear tires

(click to expand)

Gear RatioGearSpeedRPM

40 MPH in 4th

3.154th39 MPH2,000 RPM

3.454th40 MPH2,250 RPM

3.734th41 MPH2,500 RPM

70 MPH Cruise

3.156th70 MPH2,400 RPM

3.456th70 MPH2,650 RPM

3.736th70 MPH2,875 RPM

5th Gear Speed at Redline

3.155th169 MPH7,000 RPM

3.455th154 MPH7,000 RPM

3.735th143 MPH7,000 RPM

Why 5th? Because 6th does not have the mechanical advantage to get past wind resistance at these speeds - it is more of a cruise/overdrive gear. Using 5th for comparison purposes is much more relevant than having to take into account wind direction, resistance, grade, elevation, tire sizing, etc. These numbers are for comparisons among gear ratios only, not to determine what your M5 will top out at.

Limited Slip Options We can rebuild the internals and bring it back to a perfectly-functioning unit. Or you may choose to lose the variable lock in favor of a traditional clutch-type or helical diff with a set locking. We also build diffs with Quiafe, Kaaz, and OS Giken (favorite of the Turner racing team) limited slip units.

Core Charge. If we are building a diff from our own stock a refundable core charge will apply until we get your original diff back. You have a maximum of 30 days from the time you receive the diff to send it back us for a refund. Click here for more detail and explanation of the core charge.

FAQ: For a full FAQ on the custom diff process, click here.

This item fits the following BMWs:
1999-2003 E39 BMW M5

Loading Kit Configurator

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Kit Configurator

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Add REM bearing polish?

Add REM ring & pinion polish?

Core Charge

Select a diff ratio:

Select a limited slip type:

Base Differential

This Part Fits the Following BMWs

Make Model Submodel Engine
BMW E39 M5 S62 5.0L
*The above product applications have been written by Turner Motorsport. All warranties, product application, fitment, and performance are the responsibility of Turner Motorsport. For additional information see the terms of use.
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