I have an out of balance problem in my HG, it starts to vibrate at 120km/h. I have just swapped wheels with my Brougham today to check that it wasn't a wheel balance issue but the vibration remains. I guess this means a tail shaft problem. I had a quick look tonight and it appears that the spline is pushed all the way into the gearbox with the car sitting unloaded. Maybe the shaft is to long? How much room to move should I have with the car sitting on its wheels?