I replaced the front and rear pads on my 850 turbo with a respectable after-market brand. Its the second set of pads on the rotors and they were all within the thickness tolerance. I reused the shims at the rear and greased on assembly. After a careful "bedding in" period the brakes work well in all but one instance, when braking going down hill there's often a disconcerting vibration which I'm convinced is from the rear as there is no feedback through the steering. The attitude of the car when the vibration occurs is such that most of vehicles weight would have been transferred to the front leaving the rear brakes with little to do.

I will be very pleased if someone could help me on this one.

There is a known service problem that causes the rear brakes to vibrate. A new spec rear brake rotor is available that solves the problem. I had these fitted - no more vibes.

If cost is excessive in NZ try having rear discs ground (instead of machined) to enhance beddding in period and even wear.