IMHO Ford doesn't want to invest the time, resources, and capital to resolve. This issue has been complained about at nauseum for years on the 6.5' bed configuration trucks.
I have a 2 piece rear driveline. In all my research and trial lead me to a few possible suspect areas. Some are easier to address than others.
#1 Yoke phasing
#2 Driveshaft and U-joint operating angles
#3 Transmission mount
#4 Less than "best" configuration (carrier bearing/slip yoke)
I sorted through industry known best practices from Spicer and other sources on proper driveline operating angles and configurations.
The yokes should either be in phase, or 90 degrees out of phase depending on configuration. My best assessment was my config was suppose to be in phase, found the factory had a 16 degree disparity. I separated mine and clocked it at 1.6 degrees which is within the 3 degree specification. This helped some. Documented the video before and after evidence (non-scientific).
The OEM driveshaft run-out acceptable specification seems to be less than optimum.
Using a Spicer white paper. Found that my configuration didn't match any of the suggested angle ranges of operation. The Spicer specification calls for the jackshaft (shaft directly connected to transmission or transfer case) to be at the same angle as the pinion. I added pinion shims, to bring the pinion nose up, dropped the carrier bearing 1/4" and finally rigged the leaf spring isolators to engage the above leaf sooner in the travel range. This has helped immensely. Need more miles on it to validate. Haven't tried this setup with any real payload in the bed yet.
The stiffness of the transmission mount seems woefully inadequate to quell most all motion induced to the driveline, which allows any movement of the components to pick up a repeated oscillation, felt as a vibration. There are numerous videos on youtube that document this issue. Most prevalent from a dead stop, gets worse when load is applied, doesn't aid, quell or prevent the oscillating vibration at speed.
The "better" configuration driveline for those with a two piece rear shaft design is a fixed carrier bearing, double cardan joint and a slip joint build into the rear most shaft. This setup is around $600 to $750. Last resort for me. This would resolve the slip/bump/clunk compliant and having to lube the carrier bearing slip yoke on intervals. The double cardan joint would also totally resolve any phase induced vibration.
Youtube is loaded with best practice information, education and demonstration videos on proper driveshaft setup, phasing, angles of operation. The physics involved is amazing for what appears to be a simple component.
In summary on my truck there appear to be many small suspect areas that contribute to the larger experienced issue.
'13 F150 4x4 EB MaxTow
Last edited by joedotmac; 05-21-2015 at 11:42 AM.