1999 Ranger, 2 wheel, auto with 3.0L and 175000. Original owner. When I take off from a stop I feel a brief 1-2 second vibration from somewhere in the rear of the truck. It feels like running over a washboard.

It is very brief and is gone after about 5-10 feet of movement. "Shotgun" start is worst, if you "turtle" start its not there. Straight vs turning doesn't seem to matter. As mentioned very brief and only at start from dead stop. Acceleration after truck is rolling is all good and smooth.

It has been really nice here lately so I rolled the window down and I can hear absolutely no noise from anywhere. I only feel it.

Im going to change out the rear diff fluid and add the friction modifier since this seems like a possible cause but any other ideas / solutions are very welcome. TIA.

 

Inspect your rear leaf spring shackles to make sure they have not rusted or worked loose from the frame or springs.

 

This is a common problem... It can be transmission shudder, driveline/ ujoint, or spring wrap/axle hop.

What condition are your rear shocks in?

 

I bet you'll find the driveshaft slip joint needs greasin'.
Let us know what ya find.