I've got the clunking too. Usually from a dead stop, but i also have a different clunk. When idling a little higher on a cold start, if i put it in reverse, it make this horrible clunk that sounds more like a pop, as if something is slipping or under stress.

 

Just wanted to thank the OP for this thread and all the contributions it has received, I have had this problem since I bought the truck(at 88k miles, now at 92.5)and I figured it was normal, but after wanting to blame this obnoxious clunk and jerk it caused also I believe it blew my rear pinion seal.

So after replacing the seal, and then settling with the clunk till I was bored one day and decided to search on this problem, low and behold I find this thread(as well as multiple others also). I couldn't find Teflon grease anywhere(one guy at Advance auto said that all major corporations stopped selling it cause its been known to cause cancer, and the Ford dealership had no clue what I was talking about when I asked.) so I had to settle on some Mag 1 White Lithium Grease(seems to be working thus far, we'll see if I might have to make a trip to the bike shop which is apparently the only place around that sells Teflon grease still.)

Once again saying thanks for the great help this forum has always provided, great people here.

 

05 F150 FX4 78K miles.

Mine did it new, maybe 2,000 miles.
Dealership took a peek and lubed it, went away until.

Now (78K miles), Dealership took a look, lubed it and said there were some metal shavings but not that bad. They said I'd probably need a new Drive Shaft in a couple years. They said there wouldn't be a catastrophic failure but just more consistent clunking down the road.

I'm kinda pissed, this should not have happened at 2K miles or
78k miles. I would think that major part should last much
longer than that.

 

You are welcome! Makes me happy knowing it might of helped someone else

You would think that huh?

Awhile after this thread was made I blew my transmission. I rebuilt it with a lot of aftermarket parts and the help of Horgan's Transmission Shop. One thing I was surprised with, was the transmission internals, and what junk they are. The clutch discs are TINY for such a big truck. I have seen larger in small passenger cars. The quality of the sun gear was less then what maybe should be. The pump is made to flow the least amount of fluid to keep the thing alive. Towing and large tires can quickly overwork them and eat up clutches it seems. This is almost 2 years old (the thread) and my new transmission is getting close to a year old. Works GREAT! With plenty of line pressure, hard efficient shifts, all new internals, and no dang clunk! Wish I could have found out what actually caused it, but replacing to a well built aftermarket unit seemed to make a world of a difference. And I did not replace my drive shaft.

I still worry about that little slush box though