As with all disc handbrake systems, the pads and sliders are very prone to filling up with road dirt ans seizing them. Basically the pads nead to come out for cleaning, together with the calipers - which don't need to be disconnected from the car. The pistons will need to be rotated to wind them back in. When the job is done, ensure that the cable pull levers are right back before adjusting the cable if you need to.
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