20 degrees ?????
 

I just completed rebuilding all of my brake calipers. What is so magical about ATE's direction of having the pistons oriented at 20 degrees?

prevents squeeeellll.

it's easy to make a tool yourself with a protractor and some cardboard or sheet metal or thin plywood.

Or use MS Paint. If you do a search using my name, you will find instructions on how to make the tool if you don't have a protractor.

I made one using my "angle finder!" I was asking because my faulty logic tells me that the 'notch' should point down to release accumulation of water when it rains. I guess after 20+ years, even stainless would be 'stainless-no-more.'

To answer the question...the rotation is important because the pucks are not "square" to the rotor...it's kinda lopsided to provide more ( or less?) force on the leading edge vs trailing edge of the pad. Doing this evens-out the wear of the pad. If the orientation is incorrect, then the natural tendency to get uneven wear will be made even worse. Both Porsche and Mercedes sell a little tool for this for about $10.
---Wil Ferch

Well, IN MY car there is a tire covering the brakes. ;-)

Don't worry about any accumulation of water. The only time water could theoretically be trapped is when the brakes are applied. Otherwise there is a small gap between the brake piston and the disk.