and reduce the load on the transmission and differential bearings. Because U-joints are not constant velocity, they can induce vibrations when the angles are out of limits. In a one piece driveshaft, the ideal set up is to have the down angle at the transmission equal to the up angle at the differential. In this way the changes in velocity at the transmission are canceled at the differential and no vibrations occur. Minor variations are acceptable. In a two piece driveshaft with 3 u-joints the same rule applies and the angle at the center joint should be as close to zero as possible. In the Z32, the center bearing is mounted is rubber which is affected by the heat of the cats will sag causing a change in the angles and vibration. In Apr 93, Nissan issued a TSB which specified a new center bearing with improved rubber support as a fix to this problem. Note that any sag in the tranmission support could also change the angles and cause vibration. The best solution appears to be the lightweight one piece carbon fibre driveshaft.
