There's a little ratchet device in the calliper piston,
And it operates via the calliper quadrent lever.
Idea is every time the H/brake lever is pulled on/off this ratchet moves the piston out a little to compensate for pad wear.
This calliper lever HAS to return to the off position when the H/brake is off.
What I usually find is some monkey has tightened up the cable which will give you a hand brake for this years MOT but will result in the little lever siezing in a part on position.
Next year it's new callipers time.
I couldn't tell you how many rear brake mot failures I fixed because of this miss adjustment of the hand brake cable free play.
the pistons have to move out!
That's also why a wind back tool is needed to fit new pads,
The piston has to be set to "zero".
Correctly set up and adjusted ALL rear callipers will pass an MOT.
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