Just rejoined this Ford gang after years absence. Used to own "The Muny Pit", a '79 F-150 4WD monster with a '69 429... constantly breaking something. Anyway, back in search of ideas where to look on my '08 F-150 XLT 4WD with a 5.4, 83,000 miles. Searched the search bar for my title and found a post on an '00 Expedition describing similar issue than mine... for about 6 months now when I accelerate either from stop or a crawl; forward or reverse; more so when turning, but does do it wheels straight - upon inital acceleration I have this horendous rumble / shudder in the truck, like the grinding metal bearing sound/feeling felt when the pinion bearing went out on my '79 (only felt it seconds before the 9" rear pumpkin exploded). Once rolling it stops. I have checked all wheel bearings.. I have check all the suspension joints... everything looks fine, no obvious issues. The only suspension mod I've done is a 1.5" leveling kit when brand new. On the Expedition two replys suggested changing the transmission/transfer case fluids claiming it cured thier vehicles, but no response as to if the guy tried this and/or if this worked for the initial poster. Any ideas?

 

I had a shudder from the rear end, particularly from a stop and when turning. It turned out to be a clutch pack in the rear differential. My warranty covered it.
BTW, it's a 5.4L 4x4 with 3.73 limited slip diff.

 

Sounds like it could be a ring gear issue or a limited slip clutch pack issue. That's whereas I would start at least.

 

Definatly rear end clutch bearings, assuming you has a limited slip rear axel, if you arent covered under warrenty still i highly recommend you try draining your rear axel fluid, and refilling with two bottles of motorcraft friction modifier in addition to the rear end fluid as opposed to just one, this fixed the problem in mine and i havent had a problem since (limited slip still functions correctly), this is a much cheaper solution than having the clutch packs replaced.

 

ditto on the rear clutch pack!

Previous owner may have had it changed and did not add the friction modifier which is a must.