As we know at BMW rear wheels are driven. BMW chose to use LSD friction type produced by ZF. All BMW models until E36, E34, E32 could be produced with the option “LSD”. Over the years, they were installed and other types as Visco LSD, locking type (EH Differential), Torsen… but this was as an exception.
Here I will explain what is the difference between open differential and LSD. Differential character is determined by planetary gear. This mechanism is designed to differential case. Here is an example of open case type and limited slip case.
The main problem of the open diff is the loss of traction. When one drive wheel is in the air or on ice or road surface with different grip, the car loses it mobility and power. Rotates only the wheel which has no traction. Americans call this effect (or defect) “one wheel peel”. Anyone who has driven a car has experienced this defect, even if he did not know that’s is happening. I personally find it very unpleasant. But I’m not impartial. Limited slip differential (LSD) can transmit a certain torque to the wheel that got traction.
This can be done by using friction discs (#9 in the picture), installed in LSD case:
- limited slip case
- cover bolt
- stop disc
- stop disc
- little diaphragm spring
- diaphragm spring
- dog ear disc
- friction disc
- planetary gear
- bevel gear
- Bevel mate shaft
There is a lot of practical advantages when we talk about LSD. At first, the limited slip differential is very useful in poor road conditions such as snow, mud… LSD makes possible different road performances, donuts and having a lot of fun . The fun is guaranteed if you decide to take a turn sideways. As a man who enjoys sports driving and track racing LSD is necessary, and when it comes to motor sports is MUCH needed. This applies not only to drift, but for all track and rally disciplines. In drag racing, for example, the presence of LSD makes the start much better. The things can be almost perfect…
It is possible to make LSD with an higher percentage lock and a different gear ratio, according to the field of application.
The most amazing thing about LSD is the fact that it works completely automatically. Don’t need any human intervention, pressing buttons, etc. As someone says: self-blocking differential. However it requires a little more attention to service. If in the open diff not fundamentally change the oil (Long life), the limited slip differential requires a special oil, which must be changed frequently, depending on how you use the car and what is the main purpose.