[alfa] That step on the brake caliper pistons

["Jay Mackro" <jmackro@xxxxxxxxxxxx>]

The question was posed:

I'll throw in a question I've always wondered about regarding the brake
calipers. The Alfa manual shows a 30 degree angle for alignment of the
calipers. Does any one know what the purpose of this alignment is (brake
squeal or pad wear)?

My guess is that the step on the inside of the caliper pistons is to provide
a "self energizing" effect to the pads as they bite into the disks.  By
having the surface the pushes the brake pad NOT be parallel to the
surface of the disk, the pad is entrapped in a triangular space, and its
friction against the disk serves to wedge it more tightly against the disk.

The analogy is the leading shoes on a drum brake setup.  Drum brakes
inherently require lower pedal pressure than disks - one reason for
this is that the geometry of drum brakes allows some of the energy
dissipated from the spinning drum to pull the leading shoe into the
drum - positive feedback if you will.  The "triple leading shoe" set-up
used on the 101 Guilias was a state of the art design in its day.

If a set of stepped pistons was assembled in random order (like the
race car mentioned), if one side has the piston steps aligned to wedge
the pads between the piston and rotor as the brakes are applied,
while the other side has the step in the opposite orientation so there
is no positive feedback, then yea, the car would pull toward the
side that was braking more efficiently.

Does this make sense to anyone?

Jay Mackro
San Juan Capistrano, Ca.
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