Maybe he meant the rotor broke I have been working on volvo's for about 8yrs. and in that time I have seen some crazy things due mostly to negelect. I did get to witness on a 89 240 the rear rotor was actually worn down to the point where it split and only a ring was left. The brakes still worked on three wheels and on the split one the pads came out and just locked together. There really is no way for the wheel to brake or come off unless the axel came out of the rear and that will never happen. The studs for the wheel lugs and the bolts which hold the rear axel in are case hardened probabley equal to a grade 8.