Ok Dudes, I have an update on this whole Slip Yoke Binding phenomena. I got rid of the rear end clunk, bump, thump, however you want to describe it but it came back.
To maintain the slip yoke lubrication, I went back to injecting grease into the zerk fitting every so often and I think this was a big mistake. In my opinion, greasing the slip yoke via the zerk fitting is a waste of time and can cause you problems. When you inject grease to the slip yoke, the grease doesn't really get everywhere you need it to be. It's only lubricating the lower part of the splines and the grease never makes it up to the upper part of the splines.
Now, where it becomes a problem is if you pack too much grease in there. If the bottom of the slip yoke is full of grease, it somehow causes the slip yoke to to give you that rear end thump also. I realized this yesterday when I pulled off my slip yoke once again to investigate why my rear end thump has returned. The splines looked to be lubricated sufficiently because I pulled it apart not too long ago and re-greased it, but the lower part of the slip yoke was full of grease. So, I just took a long screwdriver and scooped up grease on the bottom of the yoke and redistributed it up along the female splines. I put the yoke back onto the driveshaft with the zerk fitting removed. I pushed the female yoke onto the male splines and bottomed it out to make sure the yoke could achieve full travel. The reason to remove the zerk fitting is you're giving the pressure somewhere to go as you slide the female yoke onto the male splines of the driveshaft.
So, what I'm trying to impart to you guys is I've found the clunk can be caused by a couple things. One, the yoke isn't sufficiently lubricated and it's binding and unbinding causing the rear end clunk. Two, additional pressure created by having too much grease in the yoke can also cause the rear end clunk.
I know it's widely accepted that people just give a few squirts of grease into the sip yoke and call it good but I know from having the slip yoke apart many times that a few squirts of grease in there is not going to properly lubricate the splines. Then, there's some that just pack a shit ton of grease into the yoke, drive it around for a while and then remove the zerk fitting and jump up and down on the rear bumper to expel excess grease. I tried the jumping up and down method but I believe you still can end up with too much grease in the yoke which I've learned first hand isn't good.
If you actually read all that, I'm impressed. I vomited out quite a bit there. Moral of the story is lubricate the slip yoke by taking it apart and using the special Ford grease and not to over-grease the yoke. The zerk fitting's purpose now is just to act as a plug to keep water and dirt out.
