I have spent hours researching this problem. I have changed the motor mounts, three times, trans mounts, three times . I have replaced all of drive train and differential bushings.. i have bought bell housing and transmission exhaust brackets. No good. My 1984 760 turbo Diesel runs smoother than my 1990 780.Here is the answer. the trans. mount is improperly designed When a new mount from Volvo, is bolted to the trans bracket the mount squashes down,slightly, but enough for the trans, bracket to touch the metal sides of the mount... Its hard to see but if you have this problem check it out.We shimmed the trans. cross member down and the trans up. to avoid the trans hitting the floor pan. fixed the problem.