...or maybe not so weird, given my inexperience with these things. (In the past year, I have acquired 2 junky old Volvos for the price of scrap metal, and now I'm trying to make them roadworthy.)

This is a 1989 745. It makes a grinding noise on takeoff and a thumping noise at speed. It also whines a little at speed, but not a high-pitched whine like a wheel bearing. I have attributed those problems to the driveshaft, which has some play in it when shaken. When I depress the brake pedal, it makes a clicking noise. I haven't investigated that yet. It also pulls to the right. Haven't really thought much about why that is either.

Earlier today the brakes failed. The failure was accompanied by a click, but not by any other untoward noise or smell. During this event, the car pulled hard to the right. Afterward, everything returned to "normal." There was no noticeable loss of brake fluid.

Rotors look smooth to me. I think this might be problem with the brake booster and associated vacuum parts. Not sure how to attack that problem. Maybe I could replace the booster. Do 740s have a booster check valve?

Or might the problem be at the caliper or cylinder?

I should note that while the brakes failed, it didn't seem like some of them worked and some of them didn't--there was just no stopping.