Directionality: Brake pistons and rotors?

[Ianvwsb73]

Do the pistons in the calipers have a direction that the raised portion should be pointing? I'm rebuilding the rear calipers and want to be sure I have them goin the right way, but I'm not sure how that is.

Are the vented rotors directional? How can I tell which way they should be going?

Thanks in advance. -Ian

[Ianvwsb73]

This is what I found through searching, but can anyone clarify?

Some calipers utilize pistons with a notched or recessed surface that presses on the brake pad. The purpose of the notch is to attempt to even out the pressure applied to the pad, since the leading edge of the pad would otherwise do more work than the trailing edge. When installing these type of pistons, orient the notched portion such that it faces the leading edge of the pad. This would generally be facing upward if your caliper mounts on the leading side of the rotor, or facing downward if your caliper mounts on the trailing side of the rotor. To be more technically correct, there is a Porsche alignment tool to set the orientation, but the above guideline will get you pretty close.


I'm looking for up/down front/back. Directional, I'm not sure I know which is the trailing edge etc.

Any help is appreciated. Thanks.

[Porsche944]

Ivan:

You are correct, the "notch" in the piston should be facing into rotor rotation (car moving forward). This does in fact shift braking pressure towards the trailing edge of the pad, which reduces leading edge wear and "pad skip."

Porsche has a "special tool" P84 for setting the piston angle.