Welding My BMW’s Differential for Maximum Drift
Fire up the welder
Aftermarket limited-slip differentials are expensive, especially for BMWs. Unfortunate, but fortunately, the solution is simple. Since drifters prefer having an aggressively locked differential, the solution is to make the differential 100% locked, all the time. To that end, I need to first fire up the Harbor Freight welder.
By opening the differential casing and welding the gears together, an open differential is transformed into a 100% locked-at-all-times welded differential. This is a cheap and easy trick that drifters have been using for years to get slideways.
Welding a differential is a straight-forward process, but some care must be taken, at the same time. The gears inside the diff have to be very clean, or there is a risk of the welds being contaminated and failing. Differential oil is very slick, and is a pain to clean up. After a few cans of brakekleen and a roll of paper towels the diff is ready for welding. The gears inside the differential are large, and, being gears, are oddly shaped, so welding them together can be a bit tricky. Some people take small square plates of steel and stick them in between the gears for an easier target to weld. This is referred to as plate welding the diff. See the left-side image above.
After the differential gears are welded together allow a few hours of cool-off time and then refill the diff with oil and reseal the differential cover. Job done.
My freshly-welded differential
So, I have my ready to rock welded differential, now let’s talk gear ratios. My E46 is a manual transmission-equipped early model 328i. These cars have the laziest rear end gearing of any E46 ever sold. This 2.93 diff makes for excellent freeway cruising as the engine RPMs are quite low, however, it also makes the car’s gearing very long. By my math, second gear goes to over 70 MPH. I will have to do a few events and see how the car drives with this long gearing. It may be fine, it may prove too long-legged for this stock engine, 190 horsepower family sedan to get handily sideways.
Fortunately, BMW sold many variants of the E46 3-series, with many different rear end gear ratios. If this 2.93 diff proves not aggressive enough on the track, I can easily source another differential. There are 3.07, 3.15, 3.23 and 3.46 differentials readily available in the junkyard that should be plug-and-play.
So, there it is. I have a welded differential, and a nearly-ready rear suspension set to go back into the car. Follow along with Project BMW E46 as I continue the repairs and upgrades to get it drift-ready.
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