Alpina Bavarian Motorsport Differential Rebuilding

If you have a limited slip differential, we can also refurbish the limited slip carrier while rebuilding your differential (additional charges apply). As BMW limited slip units wear, the percentage of lock (25%, 40%, etc.) gradually drops off. We can restore your limited slip assembly to original lock, or increase it to 75% for Race Track performance applications . The reduction in slippage will lower your differential lubricant and bearing temperatures as well as your lap times!

Differentials with normal wear do not usually require replacement of the ring and pinion gears. Our standard rebuilding includes complete disassembly, thorough cleaning, close inspection of all parts, replacement of all bearings, seals, gaskets, crush sleeve, and lock ring. Our rebuilding includes meticulous attention to correct gear lash, gear contact patterns, precise pre-load of bearings and exact torque specifications. We provide a 1 year/10000 kilometre warranty with our rebuilds, but expect them to last well over 100,000 kilometres.

If you want to change your differential gearing or add a Quaife unit, combining these operations with a rebuild saves you both time and money.

Alpina Bavarian Motorsport Differential Gear Ratio Changes

Changing to a quicker diff ratio provides faster acceleration in all gears at all rpm's. It does not affect engine emissions or idle speed and can make up for changes in tyre diameter. Some BMW models were originally geared very long for increased fuel economy. These cars benefit the most from quicker ratios.

Generally, longer ratios yield better fuel economy and shorter ratios offer more acceleration and higher fuel consumption. In practice, the fuel difference is often slight. If you have such a long ratio you must frequently downshift to pass or accelerate quickly, then in reality you do not get the theoretically higher fuel economy that the longer ratio would have you expect. And, if you switch to a shorter ratio for more acceleration, you may not burn much more gas than before, as you are now able to upshift more quickly into the higher gears.

In a similar way, you would expect that changing to a shorter ratio for more acceleration will reduce your top end speed as you would run out of revs in high gear. However, few cars have enough top end torque to pull full revs in high gear nor do Australian road rules allow for such speeds anyway.

Drag, rolling resistance, tyre characteristics, spoiler packages and engine modifications all affect acceleration and achievable top end speed. And don't forget road conditions, speed limits, and Australian road rules. It is usually more practical to gear for greater acceleration than higher top end speed. You can enjoy it more often with fewer penalties.

We recommend a +/- 10% gear ratio change for most street driven cars. To obtain a percentage change, divide your original gear set ratio by your proposed new gear set. The resulting percentage also equals your RPM change at a given speed.