Greetings Car Talk people! I am trying to isolate a vibration that has developed when I reach 40-45 mph and dies out after 50-55. New carrier bearing seems to have helped, but not entirely. The torque converter was recently changed as it was cracked and leaking tranny fluid. The vibration existed before and after the swap, so the torque converter is likely not the source. The torque converter locks up on this model at 40 mph, but I’m thinking it must not be locked when cruising in neutral above 40mph, else the engine would continue at high rpm rather than slow to idle speed, so any torque spinning the driveshaft when cruising at highway speed in neutral would have to come from the differential. This is where my knowledge is deficient. Can anyone shed some light on this for me? At 45mph, say, does the driveshaft continue to spin at the same speed when the tranny is shifted to neutral and the vehicle maintains the 45 mph, say like on a slight downslope, or does it slow appreciatively? Knowing which behavior takes place would allow me to rule the driveshaft in or out as a source of the vibration, as the the vibration continues when shifting into neutral at 45mph. As in the past, looking forward to the benefit of the collective wisdom of the Car Talk community.
87 Dakota V6 auto trans