In Reply to: Is LSD on 540iA Sport via ABD or conventional posted by Kirk S on August 11, 1999 at 15:17:43:
: Anyone happen to know which technology BMW utilizes to achieve LSD (limited slip differential) on the MY'00 540iA Sport (with Steptronic)?
: Is it via conventional clutching inside the rear end differential unit or is it via ABD (automatic brake differential) which essentially uses the ABS controls sort of in reverse mode to quell wheel spin on whichever rear wheel breaks loose?
On the "Pulse" section of the www.bmw.com site, there used to be a huge section on the E39, probably put up back when that model was relatively new. If you can find your way there, you may find the answer. I seem to remember that the site explained the AST, but since the site was written back when in Europe there were two options (i.e. ASC or ASC+T), it explains the difference.
From what I remember, they described the differential braking function of ASC as also effectively acting as a limited-slip differential. (The "+T" option, added to ASC as an extra cost option, adds the ability to reduce engine torque. AFAIK, in the US, only the complete ASC+T was available, so it was simply called AST for the US market.)