does the rear calliper piston squeezes?

It probably winds in with a special caliper winding tool.

Hi, Welcome to the FF.

You don't need a special tool, Spider, and all early Fiat, rear calliper pistons will wind in with a large screwdriver.

First release the handbrake cable from below the car. (nut #6 in the handbrake diagram).

Then use a large screwdriver in the wide slot in the middle of both pistons to wind them in clockwise. When the pistons are fully wound in, the wide slot should be horizontal and the narrow groove in the pistons ("A" in the calliper diagram) should be at the top. When everything is reassembled, adjust the handbrake cable.
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hi sir davren. I'm new here and i've register because of this thread since i have the same concern. I've seen this bertone repair question,what did the guy meant when he said that "maybe the master cylinder piston was binding"?

I've no idea why he mentioned "thought maybe the master cylinder piston was binding". The master cylinder is nothing to do with retracting the calliper pistons.