needing advice. i have a 78 terra 196 4speed whe i drive it a few miles in 2wd all of a sudden it sounds like the tcase has exploded and shakes violently i can stop and shift it into 4wd and its fine.... or come almost to a stop and pull into 4wd and the noise and vibration goes away... anybody have this issue or know whats going on??? thanks in advance.