Limited Slip Differential

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Limited Slip Differential From E30 Zone Wiki Revision as of 17:14, 26 July 2009 by 91.149.179.60 (Talk) (diff) ←Older revision | Current revision (diff) | Newer revision→ (diff) Jump to: navigation, search

For a general description of Limited Slip Differentials, and how they work please see the External Links below.

Generally Limited Slip Differentials are referred to as a Slipper or as an LSD. This contrasts to the normal differential fitted that is known as an Open Dif.

E30s with LSD as standard

   * 325i Sport
   * M3 

All other E30s has an LSD as an option.

LSD was *not* standard fit on the 318iS

E30 LSDs are clutch plate type and require special oil - see below.

Case sizes

E30s had two differential case sizes, they are interchangeable and the same width but will require adjustment of the prop length. Please see Fitting an E30 Differential.

E30s used either a Small Case or Medium Case differential. Other models used a Large Case which is not directly interchangeable but the internals can be swapped.

E30 LSD Ratios

Below is a list of ratio and cars in which they can be found.

   * 3.15 - M3
   * 3.64 - prefacelft 325i
   * 3.73 - facelift 325i
   * 3.91 - facelift 325i touring, cabrio, 325i with getrag 260 sport
   * 4.10 - found optionally on UK spec 318i/318iS 2/4dr in Small Case, and on all US M3 models in Medium Case.
   * 4.27 -
   * 4.44 - 

Please update the list of ratios and what cars they are found on and common case sizings.

What these numbers mean

Higher number == shortened gearing (quicker acceleration, more gear changes). Lower number == longer gearing (slower acceleration, longer time spent in each gear)

How to identify and test an LSD

To identify and LSD one can first check for the presence of the tag on the rear casing. The ratio on this will be prefixed with an S for LSDs.

Alternatively one can jack up one rear wheel, ensure the car is out of gear and hand-brake is off then turn the raised wheel. Resistance on that wheel would usually indicate an LSD. An alternative method is to try to leave skid-marks pulling away on good tarmac, two tyre marks for more than a few inches would indicate a properly "locking" LSD. This won't work so well on grass or gravel as on loose surfaces both wheels can slip easier even for non-limited slip differential types.

What oil to use for your LSD

The BMW recommended oil is Castrol SAF-XJ

You can find supplies from <please update>

Durability, Rebuilds and Upgrades

<please update with details of rebuilders in various locations, recommended rebuild intervals etc>

External Links

   * Wikipedia's Limited Slip Differential Entry
   * How Stuff Works - Differentials
   * Video of open and LSD rotation