I've found out what was the problem.
As demuire said, the calipers are sliding calipers and it's not only the piston that should be pushed back.
Also where the two bolts (on the caliper) go should be possible to push back when putting back the caliper. They should slide back easily.
So I have to take them apart, clean and put on some copperpaste.
I went to a toyota center today and asked about it and they were helpful.
Thanks to all you here on rollaclub for helping out.
robe.