you can access the adjustment without taking the disc off
to tighten you turn clockwise- but because of where the access 'window' is, you have to turn it differently on each side,
the hole to access adjustment has rubber grommet over it
the adjusting wheel has lumpy bits (like castellations)
you push the wheel with a screw driver- either levering toward you or pushing away - as wheel is perpendicular to disc (horizontal)
get a torch and try to see what is going on it there..
im not sure but i think i jacked both rear wheels off the ground, put vehicle in neutral, handbrake off, turn one of the adjustment screws a bit / then test- you want the brake to come on by 4th click apparently
btw - im definitely not a mechanic (any only tried this on AU wagon - disc brakes no
IRS)
if you dont get any joy you can take disc off then you will see what is going on...........