La razon? es mas facil conseguir pastillas y pastillas de competición (tipo Ferodo etc), para colocar en las mordazas de E30, ademas que el funcionamiento general es mejor.
Transfiero el brico en ingles, y si hay alguna duda la voy respondiendo por acá.
www.bmwe21.net escribió:Upgrade to E30 rear brakes for 323i.
It is easy to replace the 323i's rear calipers with E30 examples. They work better and there are still some performance pads available like Ferodo DS2500 that I chose.
Required mods:
1. brackets need to be made slightly thinner where they bolt on to the trailing arm to get it centered around the disc, to abt 14.3mm thickness. Use the original E21 bolts.
2. thread of those holes needs to go (drill to 10mm)
3. notch between these holes needs to be removed.
Required brake hoses: E30 examples instead of E21. Stock size fits, slightly shorter looks better but stock hoses fit ok already.
Discs can remain stock E21 323i.