I found that jumping up and down on the bumper doesn't give enough travel movement to purge out enough extra grease to do any good. The best way to get out the maximum amount of extra grease and leave a large air pocket is to remove the zerk, unbolt the drive shaft at the transmission flange and collapse it to it's fully collapsed position. It'll take a lot of pushing, prying and swearing, but that grease will get forced out. It's about a 2 to 3 inch travel as best as I can remember. You'll have to support the shaft with a jack stand while doing this.
Then with the zerk still out, pull it back into engagement with the transmission flange, which will suck air back in through the zerk's empty hole, bolt it back up and re-torque the 4 nuts to 65 ft/lbs and reinstall the zerk. This is similar to the way I greased my drive shaft. But what I did was all the the above, but I actually forced in the grease into the yoke while the shaft was still unbolted and fully compressed and supported by a jack stand, with a block of wood jammed between the 2 flanges to keep the grease from re-expanding the slip joint. Once grease was oozing through the seal, which took a lot of force by the way, I stopped, re-expanded the slip yoke, bolted it back up and reinstalled the zerk. That was the only way I could force grease into the spline area and still leave that nice large air pocket in the slip yoke. It was a pain, but the "thunk" went away and hasn't returned since. Since these slip yoke joints are so tight, I might have to do the same thing to the front driveshaft to ensure the splines are full of grease there too.:bigthumb:
