BMW Differential and Gearing Upgrades for BMW E46 M3 S54 (1999-2005)

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. 

Ensure the longevity of your BMW's drivetrain with ECS Tuning's Magnetic Plugs. These plugs are meticulously engineered in-house to provide a perfect fit and feature a permanent magnet attached to the plug body. The magnet effectively attracts and captures tiny abrasive and ferrous metal particles, preventing their circulation through lubrication systems. Metal particles can accumulate due to various conditions such as normal wear, machining operations, casting flaws, and stress usage, leading to excessive wear of vital components. ECS Tuning's Magnetic Plugs help alleviate this concern by trapping these particles, thus safeguarding the internal components of your drivetrain. With a convenient 17mm hex head design, these plugs eliminate the need for special tools required for OEM plugs.

Key Benefits:

• Removes abrasive metal particles from drivetrain fluid
• Prevents excessive wear to internal components
• Meticulously engineered for a perfect fit
• Features a permanent magnet for efficient particle capture
• Convenient 17mm hex head design for easy installation

Hands down - one of the best performance upgrades you can make to an E46 M3, E60 M5 or E63/E64 M6! With almost no downside you can make your BMW much quicker by swapping in a new ring & pinion gear set. The gearing used to be overlooked when planning modifications but the 3.85, 3.91, and 4.10 gears are now one of our biggest selling upgrades for the E46 M3! With a rear end gear upgrade you get the effects of adding horsepower but without adding any more stress to the engine or drivetrain. It's one of the best areas to get return from your modification spending. Using a shorter (numerically higher) gear ratio will give you better acceleration. The R&P acts as a torque multiplier, putting the engine into the power band sooner for each gear. There is an 6% increase in torque at the wheels with the shorter R&P. Want to make your car faster off the line or out of corners? Or avoid a downshift to pass on the highway? This is what you need.

The R&P can be installed on its own but for cars that have more than 60,000 miles it would be a better idea to rebuild the whole diff. The factory viscous limited slip units have a typical lifespan of 50-70,000 miles. We offer diff rebuilding with 3.85 or other gear options and you get a fully-rebuilt and serviced limited slip unit at the same time. Click here for our diff rebuild options.

3.85 Gearing Example: 2004 M3, 6-speed manual, 275/35-19" rear tires

Gear RatioGearSpeedRPM

40 MPH in 4th
3.62 4th 40mph 2,250rpm
3.85 4th 40mph 2,350rpm

70 MPH Cruise
3.62 6th 70mph 2,650rpm
3.85 6th 70mph 2,800rpm

5th Gear Speed at Redline
3.62 5th 175mph 8,000rpm
3.85 5th 165mph 8,000rpm

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 M3 will top out at.

This item is the genuine BMW part and the ring & pinion set only. You will need to have this professionally installed into your existing differential. BMW does not supply differential rebuild parts (bearings, shims, plates, etc.) so only a qualified shop that is experienced in BMW diff rebuilding should perform this installation. We also offer built differentials and exchanges, click here.

This item fits the following BMWs:
2001-2006 E46 BMW M3
2004-2010 E60 BMW M5
2004-2011 E63 BMW M6

OEM part number 33108311351

This kit includes Turner Motorsport solid aluminum differential race mounts pre installed in the differential cover for a quick install. These mounts where developed by Turner Motorsport for their Grand-Am Cup E46 M3 race cars, the advantages of solid aluminum mounts is increased suspension & drivetrain response, less drivetrain loss resulting in more wheel horsepower, and longevity - they effectively last forever. These CNC-machined mounts are a direct replacement for the stock rubber pieces, and have been lightened to remove excess weight.