My buddy just picked up a 2004 f150 fx4 5.4l. The only issue we are having is a shudder from what i think is the rear end upon turning either direction from a dead stop. With the wheel point straight it is smooth. Rolling while turning it is smooth also.

What could this be?

 

Probably has the Trac-Loc rear end (limited slip) and needs some friction modifier.

 

Added modifer and also opened pumpkin still does it. everything looked ok inside.

what gives?

 

How long did you run the modifer?

It can take 75 or 100 miles before it does it's thing.

 

does she have a limited slip rear end? because its probably your clutch packs in the limited slip. ive had mine replaced twice with exactly this same problem. ive also seen it with some other forum users.

 

sorry, i didnt see that it was an fx4 which will have a limited slip diff. im pretty sure that its your clutch packs. i had this exact problem with my 06 fx4.