the rear calipers are cable operated which actuates a cam & threaded rod shaft against the piston inside.
first disconnect both LH/RH handbrake cables & check they're lubed and sliding smoothly.
make sure the handbrake swing arms on both rear calipers are springing back after manually swinging em On with some pliers. must not remain sticking or seized on.
refit the cables, adjust the cable end nut under handbrake lever till there's no slack when fully down,
make sure the petruding pin on the inner pads are aligned with one of the 4 sided notches on the rear caliper pistons (use needle pliers to adjust piston angle),
bleed the fluid,
apply foot brake afew times to hydraulically push the piston snug against the pads and also slide the piston along the threaded handbrake self-adjuster shaft inside.
now apply handbrake and it should be on within 7 clicks.
so using the hydraulics 1st will automatically adjusts the handbrake mech while the cable system uses that final adjustment to nudge/engage the piston.
the main handbrake cable splits off into the 2 LH/RH cable via equaliser bar underneath, which has a limited amount of travel/give if there's an unequal balance.
this basically means that if one of the cables/swing arms was seized, the equaliser bar can still swing only afew degrees to pull on the other cable.
but once the bar can't swing any further and the old seized cable is stuck solid, the other unstuck cable can't be pulled any further to ensure the working caliper is fully engaged, hence why u should check for sticking mechanisms.
