I'm aware that you must receive thousands of individual truck problem questions, but I really need your help on this one. I have a Dodge Ram 1500 WS with a 3.9-liter V6. It has an annoying vibration between 45 and 55 MPH. Symptoms are a lot like bad U-joints, but the U-joints are fine and the truck only has 4000 miles on it. I've had the drive shaft rebalanced and that helped a little, but the vibration is still there.
I'm having difficulty with the dealer, and even the district representative stated that "yours is better than most". I'm hoping that you can shed some light on this problem. It just shouldn't be doing this.
If this is a significant vibration, and both you and the dealer are certain the problem is originating from the driveline, it's time to check the drive shaft angles.
But first, here's some stuff that you might want to try yourself. Unbolt the drive shaft from the rear axle, rotate it 180 degrees and then reinstall it on the rear axle flange. Sometimes this is a quick fix that will synchronize the shaft and axle balance.
While you're there, check the drive shaft "phasing". In other words, when one yoke is straight up and down, the one on the other end should be pointing in exactly the same direction. If not, this would indicate a "torque twist" of the drive shaft tube which will require replacement of the driveshaft.
Also, a drive shaft may balance correctly, but still cause problems due to excessive "run out". This also would require replacement.
Next, venture back to your dealer's service department and politely suggest the inspection of the vehicle ride height, and drive shaft vertical and horizontal angles. They should have the tools and specifications to do this procedure correctly. Any needed adjustments are obtained by the replacement of leaf springs, or the repositioning of the rear axle with the use of selected shims. Excessive improper angles (with correct ride height) which cannot be corrected through adjustment would strongly indicate frame, suspension or crossmember damage.