I just had my shaft centre bearing replaced due to the rubber dust boot splitting. They said they balanced the shaft but I now have a severe vibration at 100km/h +. It's an SS ute so the shaft has vibration couplings at each end and the centre bearing in a rubber mounted frame. Before I take it back to them I thought I would ask if anyone has any ideas about what they might have stuffed up. Thanks Steve
Check the bolts are tight on the diff pinion flange. Also make sure that all bolts are the same length and have the same amount of washers as each other. Other than that it could be that the shaft was not balanced properly or that it could have a bend in it. Good luck!