2000 zf6 noise

[Patoka]

I have a zf6 with an aftermarket clutch. Letting off and on the throttle I have a weird clunk in the driveline. Everything is tight that I've noticed. It's really annoying, and quite tricky to drive at times. Anyone have these issues? What's the cause?

 

[TheBigRig]

This could be your splines on the 2 piece drive shaft. Ive heard that they can clunk pretty bad if theyre dry. Theres some special grease to get that you put in the splines and it stops it from clunking. Poke around for some information on it. I believe I found it on the powerstroke.org forum.