Hey All,
'07 FX4, 5.4 w/3:73s and ltd slip. The truck has 122k and is a daily driver w/zero off roading. I live in the rust belt but don't plow. I've been changing fluids every 50k w/synthetic and just switched to Amsoil for the diffs and xfercase. Having a local tranny shop drop the pan every 30k and using what ford calls for for fluid. That only changes about 5-6 qts though.
I'm feeling a vibration when I've got weight in the bed and taking a turn either direction (maybe 3-400 lbs and I'm starting from a stop, taking a turn). Nothing on the highway, just from a stop. I grabbed the drive shaft and it is rock solid at the diff but at the xfercase, the shaft and xfer case move up and down maybe 1/8-1/4". Has anyone heard of a mount wearing out?

 

That sounds more like limited slip diff chatter. Did you add FORD friction modifier when you changed the rear fluid?

 

Thanks GLC.
No, I did not.
I asked Amsoil if the had a friction modifier in the fluid and they said yes.
I just spoke to the machine shop who just replaced my u-joints and balanced the shaft and they said they would add the ford friction modifier.
Do you agree with their opinion?
I have only noticed this vibration about 3 weeks ago and my fluid was changed in the fall.

 

I'm going to install the shaft later today and see if the vibration is still there.
If it is still there, how much of that 4oz tube would you put in?

 

Put the whole tube in.

 

Thanks,
So I put the shaft back in and took it to the place where I felt the vibration and I didn't feel anything.
If it was a friction modifier issue wouldn't I feel it every time I took a 90 degree turn from a stop?
I still have to see how it reacts with weight in the bed.