I tried to search the net some more, and found a post stating this. So it's just improperly used/designed/fitted pad? True? Or not quite?
http://forums.bimmerforums.com/forum...8&postcount=35
Quote:
Yes, it was improperly-used/designed/fitted pad backing plates that caused the ceramic caps on top of the pistons to crack.
You have to make sure the pad backing plates sit flush with those ceramic caps, so they distribute pressure equally. The OP used cut-up Porsche pads not designed for the 135i that caused the caps to crack. He then mistook the caps for the actual pistons, which they are not. They are ceramic caps designed to reduce heat transfer from the pad to the brake fluid.
Berk did the pads on their 135i properly and they have had no issues after several hard track days (see my sig)
So, to recap:
1) The cracking was caused by improperly-fitting brake pad backing plates. Basically the holes on the plate where the pistons are supposed to set into it did not line up with the BMW pistons, because the pads were modified from a 6-piston Porsche pad.
2) The fix? Use pads specifically designed for the 135i!
3) It is not the pistons that crack. It's the ceramic caps on top of them.
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