Additionally I read that the 4 wheel drive E9x models use a Bosch ABS system instead of the Teves, but I couldn't find any other information on that (yet). But I suppose that would make it difficult to retrofit the MK60 ABS to a 4x4 car, if it's only used on 2wd. I'm not sure why the ABS system actually needs to be different for 4x4 vs 2wd, but I know that it is on the Cosworth. Although I don't know what is actually different.