98 F-150 4.6.... I have read several different posts concerning this issue. I have had an elusive vibration that I feel during acceleration and deceleration, usually up between 60-70 MPH but not limited to that speed. Occurs usually with light throttle, that's when its most noticeable.

It started when I had to replace the rear end. Went from an 8.8 to 9.75 with rear disc. First issue was the drive shaft was too long. Several drive shafts later we have a completely new custom drive shaft installed. First one was cut down too short and that was told to be first vibration. Second one was too long and was also said to be causing vibration. Third was verified by the drive line shop to be correct in length as well as having enough pinion angle (which I am still skeptical about). The trans tail cone was completely replaced with new bushing and forced lubrication mod. There is no noise from the rear end as far as turning under power. I have driven in a circle in an abandoned parking lot. Problem still exists. Just to add to the process of elimination I was also going to have the wheels and tires checked out. Any thoughts would help.

 

I would have tire balanced. Was the drive shaft balanced when it was cutdown or made?

 

Bent axle(s)... This rear end was purchased from a local salvage yard. Most likely came out of a roll over truck (no warranty). $200 will get me 2 new axles. I will post when it is complete to verify it was in fact the issue...

 

So even though the axles were in fact out of round there still is a vibration. Feeling it light in acceleration from a stop. Feeling it more so up at speed (60-70 mph) with light pedal, and when coasting deceleration somewhere about when the torque converter/transmission disengages or shifts. Transsmission issue..? I will have to set away some time to open this thing up... Any thoughts, I'm almost at my wits end with this thing...