BMW Differential Types

BMW Differential Guide

BMW Differential Types

There are a wide variety of BMW differentials and mostly the components are not interchangeable between generations. Generally early differentials are fitted with taper bearings, and most post-2006 units are fitted with ball bearings. Both can use 75W140 oil, though ball bearings are supposed to use the thinner 75W90 for increased fuel economy. Most bearings are not interchangeable between pre- and post-2006 units. We stock all bearings prior to F-series and can service all of these differentials, and perform factory blueprinting.

We recommend OS Giken Superlocks for these differentials. For further requirements we have other LSD offerings.

215LW Spline Type

215LW Spline Type differential
  • Found in 135i, 235i, 335i, 140i, 240i, 550i etc.
  • Fitted to all DCTs, automatics and manuals after 2008
  • Uses all ball bearings
  • No side covers
  • Symmetrical output shafts
  • Often has a welded ring gear
  • Generally all open differentials
  • Requires cutting and drilling for LSD fitment

Size: 210mm / 215mm

188K differential
  • Found in E36 M3 3.2L, E39 M5 and E46 M3.
  • Uses all taper bearings
  • 8-bolt side covers
  • Symmetrical in E36 and asymmetrical from E46 onwards
  • Fitted with a 2-clutch LSD or M-Variable Viscolok LSD
  • Takes 210mm or 215mm ring and pinion sets

Type: 188K

188mm differential
  • Found in E39, E53 and E46 6-cylinder vehicles.
  • Uses all taper bearings
  • No side covers
  • Updated 'K' style output shafts
  • Takes 188K ring and pinion sets only
  • Accepts all 188K and 188LW style LSDs
  • Never fitted with a LSD from factory

Type: 188mm

168mm E30/E36 differential
  • Found in E28, E32, E34, E36.
  • Uses all taper bearings
  • 6-bolt side covers
  • 8-bolt rear cover
  • Uses 188mm style LSDs
  • Uses 188mm style ring and pinion sets
  • Standard offset 3.15 to 4.88
  • High offset is 2.79 to 3.07, and 5.00 to 5.44

Type: 168mm (E30 / E36)

168mm E21/2002 differential
  • Found in E30 and E36 318i and 320i.
  • Uses all taper bearings
  • 4-bolt side covers
  • 6-bolt rear cover
  • Uses 168mm type LSDs
  • Uses 168mm style ring and pinion sets
  • Two different carrier offsets depending on ring and pinion offset

Type: 168mm (E21 / 2002)

168mm E21/2002 case differential
  • Found in E21 and 2002.
  • Uses all taper bearings
  • 4-bolt or 6-bolt side covers
  • Uses 168mm type LSDs, though three offsets exist
  • Uses 168mm ring and pinion sets
  • Two different case widths exist
  • Three different carriers exist

BMW LSD Types

2-Clutch LSDs

For cost and simplicity reasons, most vehicles had a simple 2-clutch LSD unit fitted. They feel smooth and remain quiet and tight for a long time because they have two disc springs installed at each end. One large pair compresses the clutch plates, and keeps them under compression even with considerable internal wear. The second set of disc springs compresses the floating differential assembly (splined gears, spider gears, thrust bars). They typically have 45-degree angles cut into the thrust plates.

2-clutch LSD lockup graph

This graph demonstrates the lockup curve by plotting the thrust angles versus the lockup percentage. It can be used to roughly work out what angle to cut to achieve a desired lockup for a 2-clutch unit. For example: 30 degrees ≈ 40% lockup, 35 degrees ≈ 35% lockup, 40 degrees ≈ 28% lockup.

There is really only one angle worth grinding to, and that is 30 degrees — lockup increases only slowly as the angle approaches 30. Considering all of the surface grinder work, lathe work, heat treating and blasting involved, the 30-degree angle is the only choice that represents value for money. This machining work raises the lockup by 15 percentage points, and turns the 2-clutch LSD into a good performer for only a small investment. Rebuilds are inexpensive, as there are only two clutch plates and two steel plates to replace. This configuration is very popular.

4-Clutch LSDs

For improved performance, some BMWs had a 4-clutch LSD installed as OEM equipment. These were a rare fitment, and had comparable lockup to a 2-clutch unit at just 40% on drive. Unlike the OEM 2-clutch units, these did not have the large disc springs to compress the clutch plates. Due to their \"unsprung\" design they had little to no preload, and may show close to zero ft/lbs breakaway torque. For some drivers the improved turn-in is advantageous, though the low breakaway torque makes it more difficult to ascend uneven driveways and other uneven surfaces where one wheel may lift. The unsprung configuration reacts quickly and feels direct, and most drivers would prefer this — though the lack of springs means that if the LSD is custom built with, for example, 60 ft/lbs of breakaway torque, it will degrade down to zero ft/lbs over time. For race vehicles, this is the price paid for the unsprung build. The use of one spring instead of two gives something in between, depending on how much the spring is compressed. Measurements need to be taken very carefully in this case, because the entire stack is being pushed in one direction, which could put pressure on the splined gears — which should be floating, and never touching a thrust plate.

There are a few different custom 4-clutch options, which all have relatively high lockup starting at 45%. The graph below plots the angles in degrees versus the lockup as a percentage.

4-clutch LSD lockup graph

Using this graph, it is possible to determine custom lockup angles for any amount of lockup required.