Candidate for Bodsy's Brake Bible.
I think if you have not yet, then now is the time to download and read what is called Bodsy's Brake Bible. It is a free 36 page pdf that tells you about all you have to know about fixing the brakes on a 3.
The odds are your problem is inside the dual rear parking brake drums, (yes drums), and if so, it will be a show stopper sooner rather than later.
Link on disco3 to Bodsy’s Brake Bible
http://www.**************/gallery/thumbnails.php?album=4184
Replace the **** with
disco3 co uk and insert a period between each of the two spaces. Blocking you know.
Download the latest version; v1.6a as of when I typed this.
Bodsy keeps updating it as he tunes the pdf up.
The best part is probably towards the end re the electronic parking brake.
It is black art stuff, (well leading edge); also the set and unset procedure applies when doing just a normal rear pad change.
If you ignore the set unset procedure, then a few miles down the road, the squealing will start.
The fronts are more normal, but the rears, not!
You actually have three pair of brake assemblies to deal with, the front pair of rotors, and pads, the rear pair of rotors and pads, and then the parking brake pair of drums and shoes – yes, drums and shoes. That is why you can use the parking brake as a “dynamic” system to safely slow the vehicle from highway speeds. The owner’s handbook explains the procedure.