BMW Differential and Gearing Upgrades

Servicing your rear differential at regular intervals is important to ensure you maintain both performance and a long lifespan. Over time, the differential fluid can break down, lose its lubricating properties, and become contaminated with metal shavings and debris. Regularly replacing the fluid ensures that the gears and limited slip differential clutch packs are adequately lubricated, reducing wear and tear. Regular maintenance also helps identify potential issues before they become major problems.

This kit includes Genuine BMW differential fluid designed specifically for your M Sport differential and a brand new fill plug. The factory plugs include a rubberized seal that compresses over time and may not seal properly when reused.

One unique aspect of performing this service is the removal of the lower differential temperature sensor. Unlike many typical BMW differentials, this differential does not use a traditional drain plug and instead uses the temperature sensor as a drain plug. This sensor is removed to drain the differential fluid and is replaced before refilling. If you'd like to replace this sensor as well (not included in this kit), please see our recommended items or search BMW part number 33107847469.

NOTE: This kit includes 3 500ml bottles of diff fluid. BMW claims that only 1 Liter of fluid is necessary, but we found that 2 500ml bottles were insufficient. The third bottle included also allows for a minor flush of the old differential fluid before refilling.

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

Ensure your vehicle's differential stays in top condition with Authentic BMW components!

Over time, the differential fluid in your vehicle can accumulate contaminants, affecting its performance and lifespan. Regularly changing this fluid is essential, and BMW offers a comprehensive kit with all the necessary parts.

The kit includes:

Genuine BMW fill bolt (Quantity: 2) 500mL Genuine BMW 75W-85 G2 Hypoid Differential Oil (Quantity: 2)