The Stovebolt Site Forums The Shop Area Driveline Shattered Yoke Question, Driveshaft Problem.

Once the u-joint yoke failed it may have taken out the okie bushing since the driveshaft was flopping around inside the torque tube. The gentlemen that drove your truck may have popped the clutch unless something locked in the rear end causing the yoke to snap like that. Carefully inspect all rotating parts. Jack up rear end and rotate tires while listening for any telltale noises and inspect U-joint for slop since you have to remove it to replace the yolk anyway. As for the drift pin I have a similar looking slotted plug on the pass side of my 4 spd and that pin is flush with the case although I do not know how long the pin is or it's purpose