My 99 screw with a v10 runs great, but clunks as I pull away from stop signs or lights. He harder I hit the gas, the harder thit "hit". Opposite if I eas into it. I've climbed underneat it and watched the driveline as my wife worked the truck back and forth. Everything looks tight, and the shafts don't move when the truck is in park or neutral. I'm kinda thinking engine or tranny mounts?? It doesn't clunk or anything if it's in gear and I stab the gas after coasting a bit. It's been my experience with ford ambulances that the u joints are shot when it clunks then. Any ideas?

 

Have a look at this. I think this is your problem. Slip joint regreasing

 

Ditto on the Slip joint re-greasing thread!

Major reminder! Remember to block your wheels before removing the shaft!

 

That seems like a simple place to start. I wanted to ad that the clunk was a very deap sounding, almost a thud, that jolts the entire rig.

 

Give this a try. It does feel that way when the splines are dry.

 

Cool. I'm excited that the first relply wasn't something dumb that I have to pull the frame off.

 

Naaa, you just need to pull the engine and trans for this.

 

F that. I'll trade it in on a diesel before I try all that in the driveway. Haha. Hopefully the driveshaft comes off easily enough. It's got 218k on it, but runs like new.

 

Mine did the same...I pulled the driveshaft and found the splines dry...re-greased and all is well.

Rob

 

 

Ditto...on the wheel chock reminder..!!!! Don't ask how I know...but a driveshaft across the bridge of the nose, feels like a Louisville slugger. ALWAYS block the wheels

 

Haha. Well noted.

 

I know that feeling all too well. Wife came running out of the house because she heard a thud, then saw all my tools come flying out from under the truck with words that would make a Sailor blush.

 

Might want to read this.

https://www.ford-trucks.com/forums/s....php?t=1091580

 

This has been a running TSB thru Ford Motor Co for almost 20 years. Use a silicone grease and it should take care of the noise.
And look elsewhere on this site for the TSB. Ford describes the condition as a "slip-stick" condition.