Turner Custom Limited Slip Differentials - E39 540i/M5

A custom differential is one of the best upgrades to have done to your BMW. Not only can you get more performance but you can also get rid of the open diff in non M BMWs or 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.
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E39 540i Differential Upgrade - Custom Options
Diffs by Turner - Corporate Logo
T#:340169
Part#: TMS20538
Direct Ship, Expected Ship Date: Jun 29, 2021
Starting at $1,799.00
Free Shipping
Starting at $1,799.00
Free Shipping
Changing the rear gearing on your 540i is one of the best performance upgrades you can make. The shorter gearing will help accelerate the car quicker by placing the engine in a stronger part of the power band for any given speed. Being in that 'meatier' part of the power band means more torque is available at the wheels. And there is almost no downside!

The stock 540i has either a 2.81 or 3.15 final drive ratio. Both are relatively tall (numerically low) because of the 540's torque output and 6-speed transmission. But using a shorter gear (numerically higher) will take advantage of that torque output even more and give dramatically better acceleration. We rebuild the stock BMW diff with the new gear ratio, new bearings, and new seals. So not only do you get a performance improvement but also a rebuild of a potentially troublesome component. We can also add a limited-slip unit to get better traction.

By changing the gearing, you are changing the speed in relation to engine RPM. The 540i begins to make most of its torque at 2,700 RPM. With the original gear ratio, 25 MPH is 2nd gear at 2,500 RPM. With shorter 3.46 gearing at 25 MPH in 2nd you're now at 3,000 RPM - much deeper into the power band! At 70 MPH in 6th you are right at the start of the torque curve, which means you get much more thrust and maybe no need to downshift! Here are more examples of the gearing and speed differences -

2002 E39 540i, 6-speed manual, 255/40-17" rear tires
(click to expand)
Gear RatioGearSpeedRPM
40 MPH in 4th
2.814th38 MPH1,750 RPM
3.154th38 MPH2,000 RPM
3.464th39 MPH2,250 RPM
3.624th38 MPH2,250 RPM
70 MPH Cruise
2.816th72 MPH2,250 RPM
3.156th71 MPH2,500 RPM
3.466th71 MPH2,750 RPM
3.626th68 MPH2,750 RPM
5th Gear Speed at Redline
2.815th159 MPH6,000 RPM
3.155th142 MPH6,000 RPM
3.465th129 MPH6,000 RPM
3.625th123 MPH6,000 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 540 will top out at.

Limited Slip Options The 540i did not come from BMW with a limited-slip differential (posi-traction). Instead, they relied on the throttle electronics and/or brake application to limit wheelspin. The problem with this system is that as soon as it detects wheelspin the electronics cut engine power first. On later models with DSC the brakes will also be applied to the spinning wheel. And without limited-slip (an 'open' diff) it means that power is really only being directed to one wheel (not both rear wheels) - the infamous 'One Tire Fire'. Lifting the inside wheel in a corner can result in useless wheel spin, then engine power cutoff, which is futile when trying accelerate out of a corner. Instead, a limited slip differential (LSD) will transfer power from the inside to the outside wheel that has a lot more traction. We can also vary how much torque is transferred (the 'lock-up') so that you can still transfer torque and get some wheelspin at the same time (great for drifting/autocross!).

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:
1997-2003 E39 BMW 540i
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E39 M5 Differential Upgrade - Custom Options
Diffs by Turner - Corporate Logo
T#:340170
Part#: TMS20537
Direct Ship, Expected Ship Date: Jun 29, 2021
Starting at $3,599.00
Free Shipping
Starting at $3,599.00
Free Shipping

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

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Powerflex Polyurethane Rear Differential Front Mount Bushings - E39 non-M
Powerflex - Corporate Logo
T#:378989
Part#: PFR5-525
Direct Ship, Expected Ship Date: Jun 24, 2021
$41.99
$41.99

Differential bushings are responsible for keeping the differential in solid alignment while dampening drivetrain vibration. While OE rubber bushings are fine when they are new from the factory, aged and worn out rubber bushings create a multitude of issues that can range from annoying to dangerous. As a factory bushing ages, it begins to harden and become brittle. When this happens the bushing will actually shrink and allow for movement at the differential mounting point. At this point, the differential is free to shift under load causing a noticeable clunking noise under acceleration and deceleration and massively increasing the stress on the driveshaft and axles. Manual transmissions suffer the worst from this as it can make shifting difficult since the differential will shift when the clutch is engaged and disengaged.

By replacing these bushings with full polyurethane, the movement is eliminated since the mounting point is supported by a much stiffer material that will not harden or shrink over time. This means less stress on the driveshaft and axles and greater longevity of supporting components. 

Engineered to perform, Powerflex performance polyurethane differential bushings offer a supreme level of control, while still providing enough comfort for the street, with advanced polyurethane that reduces NVH that often accompanies lesser bushings. Expect improved acceleration response, more direct shifting feel and overall improved drivetrain composure with Powerflex performance polyurethane bushings.

Poweflex is a leading manufacturer of aftermarket suspension bushings. Using state of the art design and manufacturing, all replacement bushings are engineered to out-perform and out-last the ones that came in the car. Each line of bushings is meticulously tested and then re-tested to ensure perfect fitment and enduring quality through the life of the vehicle. A full lifetime warranty backs every one of their products and demonstrates the level of confidence and commitment Powerflex has to their customers. 

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Race Polyurethane Differential Bushing Set, Front - E39
Powerflex Black Series - Corporate Logo
T#:379941
Part#: PFR5-524B
Direct Ship, Expected Ship Date: Jun 24, 2021
$45.99
$45.99

Differential bushings are responsible for keeping the differential in solid alignment while dampening drivetrain vibration. While OE rubber bushings are fine when they are new from the factory, aged and worn out rubber bushings create a multitude of issues that can range from annoying to dangerous. As a factory bushing ages, it begins to harden and become brittle. When this happens the bushing will actually shrink and allow for movement at the differential mounting point. At this point, the differential is free to shift under load causing a noticeable clunking noise under acceleration and deceleration and massively increasing the stress on the driveshaft and axles. Manual transmissions suffer the worst from this as it can make shifting difficult since the differential will shift when the clutch is engaged and disengaged.

By replacing these bushings with full polyurethane, the movement is eliminated since the mounting point is supported by a much stiffer material that will not harden or shrink over time. This means less stress on the driveshaft and axles and greater longevity of supporting components. 

Powerflex Black Series bushings are the ultimate in track and race bushings. Featuring 95A durometer polyurethane, Black Series bushings are 25% stiffer than street bushings. Engineered to perform, Powerflex performance polyurethane control arm bushings offer a supreme level of control, while still providing enough comfort for the street, with advanced polyurethane that reduces NVH that often accompanies lesser bushings. Expect improved acceleration response, more direct shifting feel and overall improved drivetrain composure with Powerflex performance polyurethane bushings.

Poweflex is a leading manufacturer of aftermarket suspension bushings. Using state of the art design and manufacturing, all replacement bushings are engineered to out-perform and out-last the ones that came in the car. Each line of bushings is meticulously tested and then re-tested to ensure perfect fitment and enduring quality through the life of the vehicle. A full lifetime warranty backs every one of their products and demonstrates the level of confidence and commitment Powerflex has to their customers. 

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Race Polyurethane Rear Differential Bushings, Rear Mount - E39
Powerflex Black Series - Corporate Logo
T#:379320
Part#: PFR5-526BX2
Direct Ship, Expected Ship Date: Jul 27, 2021
$94.99
$94.99

Differential bushings are responsible for keeping the differential in solid alignment while dampening drivetrain vibration. While OE rubber bushings are fine when they are new from the factory, aged and worn out rubber bushings create a multitude of issues that can range from annoying to dangerous. As a factory bushing ages, it begins to harden and become brittle. When this happens the bushing will actually shrink and allow for movement at the differential mounting point. At this point, the differential is free to shift under load causing a noticeable clunking noise under acceleration and deceleration and massively increasing the stress on the driveshaft and axles. Manual transmissions suffer the worst from this as it can make shifting difficult since the differential will shift when the clutch is engaged and disengaged.

By replacing these bushings with full polyurethane, the movement is eliminated since the mounting point is supported by a much stiffer material that will not harden or shrink over time. This means less stress on the driveshaft and axles and greater longevity of supporting components. 

Powerflex Black Series bushings are the ultimate in track and race bushings. Featuring 95A durometer polyurethane, Black Series bushings are 25% stiffer than street bushings. Engineered to perform, Powerflex performance polyurethane control arm bushings offer a supreme level of control, while still providing enough comfort for the street, with advanced polyurethane that reduces NVH that often accompanies lesser bushings. Expect improved acceleration response, more direct shifting feel and overall improved drivetrain composure with Powerflex performance polyurethane bushings.

Poweflex is a leading manufacturer of aftermarket suspension bushings. Using state of the art design and manufacturing, all replacement bushings are engineered to out-perform and out-last the ones that came in the car. Each line of bushings is meticulously tested and then re-tested to ensure perfect fitment and enduring quality through the life of the vehicle. A full lifetime warranty backs every one of their products and demonstrates the level of confidence and commitment Powerflex has to their customers. 

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ECS Magnetic Differential Oil Drain Plug - Most BMW & Mini Models
ECS - Corporate Logo
T#:366828
Part#: 009314ECS01A
In Stock
Sale - Save 15% $34.95
$29.71
Free Shipping on orders $49 and up
Sale - Save 15% $34.95
$29.71
Free Shipping on orders $49 and up
You use a magnetic drain plug for your engine oil, right? Why not apply the same proactive thinking to the differential too? This is a direct replacement magnetic differential drain plug for your BMW. It will catch and retain fine and larger metal particles in your diff oil. If you're proactive in your diff oil servicing, you will catch a minor issue long before it becomes a headache. Diff drain plug includes one sealing o-ring. Direct replacement for Genuine BMW part number(s): 33117525064, 33110308370, 33110152626
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