e9 Rear caliper "piston" question

[Rod Cole]

After seeing how bad the front calipers were, I knew the rear needed to be gone thru. I did a search and couldn't answer my question.
Can someone tell me why they milled away a portion of the surface of the piston that bears on the pad. I did a search on the web and found rebuilt calipers and saw the same "cut-out" on all the ones I looked at, so, there must be a good reason. A second question might be, what direction must the cutout face, but I think it would move in time, so I don't think it's a matter of how it faces - but why is it there

????

 

[Belgiumbarry]

i recently had the same question.... this link was given by the forum .

http://e9-driven.com/Public/Library/BMW-E9-Manual/pages/en/34212720.html#refertoc

 

[Rod Cole]

Thank you very much for that, now to see how difficult it is to find new bolts~

 

[Ohmess]

Owners Workshop Manual states that the cutout must be in the correct position else "brake judder, squealing or excessive pad wear may result."

 

[mbmw]

ATE made a gauge to set the position of the pistons.

 

[aearch]

cut out is to keep caliper from "freezing" to pad

 

[Cornishman]

I looked into this and was told that the cutaway was added to the race cars and fitted to all cars for a while.
It was to do with the piston getting stuck by "cocking" in the bore. I don't know if this is correct.

 

[aearch]

ALL IS GOOD ive has solid round ones burn to the pad

 

[inovermyhead]

May be wrong, but I thought those pistons were for the rear calliper only and had to do with how the pistons engage with the back of the pad, I understood that the rear of the pad engages with disc fractionally before the front and reduces the initial bite and therefore noise and vibration.

John

 

[E9madada]

I agree with John, I have read the same some time back.