Caliper Rebuild, why 20°?

[emcon5]

I rebuilt the calipers on my 82 SC yesterday.

I set the pistons at the required 20° angle, as specified in the instructions, as pictured below:



What I don't understand is why. What is the purpose of the relief on the pistons, and what is the significance of 20°?

No other car I ever owned had anything like this.

Thanks,

Tom

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82 911SC Coupe

[Don in Redondo]

To aid in the release and retraction of the piston without vibration. Many other auto designers use heavy return springs and beefier piston caliper setups, that are cumbersome and require more parts to effect the same outcome.

Downside is that P. brakes are more prone to pad drag and pedal slop when things go wrong.

[movin]

I recall the same thing being accomplished by other manufactures by placing a Squeal Shim configured in similar fashion between the piston and the pad. Looks like Porsche wanted to do it the hard way again.

[orbmedia]

I thought the angle was for uniform pressure application across the pad surface and even wear.

[Roland Kunz]

Hello

The reason is that the disc has different speeds from the inner to the outher circle so this will generate a spin impulse to the pistons on the long run.

Grüsse