Going to make this as to the point as possible. I have had an issue with my super duty for the last 30,000 miles. I have replaced many parts to resolve this but none have remedied the problem. The symptoms are as follows. When decelerating, the truck shudders, shakes, and makes a horrible grinding vibration that rattles the entire truck. It is at its worse at 5mph. It doesn't happen above 20mph. It does happen when accelerating from a stop but is more noticeable when slowing. It is consistent in that it always does it. 4wd on or off, hubs locked or unlocked, throw it neutral, nothing makes a difference. This is not a wheel out of balance or anything to do with tires. It is a mechanical grind, like a failed bearing. Below is a list of all the parts I have changed. Both front hub bearings, front axle u joints, ball joints, sway bar links,all rotors, all pads, tires, lockout hubs, rear driveshaft u joint, front diff race bearings, shocks. Any thoughts would be very appreciated. It is getting worse. I'm leaning in the direction of rear wheel bearing, pinion bearing or pinion preload, driveshaft out of balance. Let me know what you all think. Thanks

 

Time to remove the rear diff cover and take a look see !

 

Any noise pitch changes when turning at speed or during chassis weight transfer in a turning bank? Or, does it change with the application/release of the throttle? At cruise speeds, any pitch change tipping In/out of the throttle slightly?

 

I'm having the grinding when I turn a corner and accelerate, it goes away for a while but returns. It has to be the rear diff. I'll remove the cover and take a look too. Not sure what I'll be looking for other than metal shavings but what the hell.
Mine is a 2009 F250 Super Duty 4X4.

 

Might be a good idea to get a tube of "RTV sealant(gasket maker) made for use with synthetic lube" , lt purple color tube. If you find metal specs in the lube when you drain and remove the cover, keep in mind all the bearings in the differential and the wheel bearings could be affected,depending on how much and the source. Lets hope it was just low on lubricant. Lube spec should be in owner's manual.