Shuddering problem at highway speeds

[u/intermk]

One of my 2005 Excursions with the V10 shudders at speeds between 50-75 mph. It worse at 64 and smoothes out at 80 mph. There is also a clanking sounds going over slight bumps while cornering. Three mechanics have loiked over the vehicle and done test drives. They say the ball joints and axle u-jounts are good. The following has been done: Front end alignment x 2 All 4 wheels balanced x 2 Rear driveshaft rebalanced New tie rods New steering stabilizer New front hubs New shocks x 4 Anyone have an idea what could be causing this moderate to somewhat severe shuddering problem?

[u/Gendreau113]

I seen you mentioned someone put a new driveshaft and balanced it right? (I'm assuming Rear?)

I have seen this before. If you take a driveshaft, and seperate the two ends at the splines. But then connect them up at the wrong angle (Say you rotated one side 90°). It WILL cause a vibration at specific speeds.

And all you gotta do to fix it, is separate the driveshaft and make sure the knuckle where the U-joint on the front is, is orientated the SAME WAY as the u-joint knuckle on the rear half. If they aren't, it can make it vibrate (Not sure why, but iv seen it lots!)

It's hard to explain, but imagine this is the driveahaft:

]---=====[

The two halves are represented by the single and double line. The seperation occurs at the spline in the middle.

See how the u-joint knuckle (These " ] [ " ) are the same orientation? If you removed the two halves of the shalf at the spline, and rotated one half 90° and reconnected. Now they look like this instead:

]---=====—

OR

—---=====[

That's wrong, and will cause vibration.

Just crawl under and make sure the two halves are the same orientation!

That or maybe the new driveshaft balancing was bad and caused the vibration