You disconnect the motor from the calliper, just two bolts. You can then, with the aid of a socket, wind the mechanism back, away from the rear of the calliper piston. Once this is done you can then push the piston back like any other calliper piston. You need to do this because the new pads will be thicker than the old ones. Here's a picture of my calliper and piston which should show what I mean.
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Excellent! Thanks! Presumably, when you put it all back together, the car just adjusts automatically to the new pd thickness and takes up whatever slack it needs to? (I think they just tend to run the motors unti lthey stall, but I'm not sure. Sometimes on the company car, I manually apply the EPB and can year the motors running for a second or so, but when I turn the ignition on, they run again, very briefly. I therefore wonder if they only artially apply themselves most of the time the car is on reasonably level ground, and then just run until they stall when you turn the ignition off, or pull and hold the switch?