I have slight rear end chatter when accelerating and turning from a stop. I am going to change fluid and friction modifer and see if that helps. 03FX4 4.6L
On my girlfriends truck 08 6.4 PS. Hers will chatter from take off. We just put a new mid bearing in. Her's obviously lays down way more torque than mine.

Any chance universals are also playing part in this shutter? Now non of ours are beat or broken, don't know if there is a tight one or not.

Thanks.

 

You can relatively easily drop the driveshaft and see if any of the U-joints are loose or frozen, but if you're getting chatter on turns, then it's likely one of two things:

1) fluid and friction modifier has broken down, replacing will help (may take many miles of driving to take effect)

2) clutch packs are worn out. no way around it, but gives you a good excuse to change the axle seals/rear bearings at the same time.

 

I have the same issue in my 03 FX4 4x4 with 5.4 engine (67,000 miles). Changed rear fluid and added Ford brand friction modifier.
Solved it!!!!
Chatter gone with a few days. U joints also checked and were fine.

 

^^^ This... use the Motorcraft Friction Modifier ONLY. Doesn't matter what the bottle says about not needing it (Valvoline gear oil claims this). You NEED it.

 

YUP
What he said