audifirst

do dealers use shims between the piston and brake pad to adjust them properly...
I believe the problem I have with squealing is there is not enough pressure on the rotor, and it touches and maybe that's why it squeaks...
I have found that my driver side pads were little bit thicker then on passanger side..
it could be that the I would need to caliper..
but I would think that this is easy fix... anybody knows...

WClark

The OEM pads have a rubber-like backing that helps keep the pad back and caliper piston from vibrating together which is a common place for brake squealing to occur. Lacking that, it is advisable to apply one of the anti-squeal compounds between the pad backing and the piston (on the inside pad) and the pad backing and bracket (on the outside pad). Most auto parts stores carry the compounds.

Other causes of squeal include improper seating of the pads (failure to surface the rotor when new pads are installed is common) and repeated light brake usage - leading to a buildup of degenerated former brake pad material on the pad. The latter can usually be addressed with a couple firm stops if squealing is heard.

The caliper piston is the self compensating element for pad thickness as is the floating half of the caliper. This is needed to avoid repeated brake adjustments. Thus a shim as you describe is pointless.