I have an 87 Dakota with a two-piece driveshaft, bought it new. A couple months ago at 140,000 miles there came a chirping noise from the rear at acceleration from a stop. I changed the u-joints with new Moogs and had a new center support bearing pressed on at a driveline shop. Reinalled driveshaft same as it cam out. The u-joint at the diff was shot, the other two not far behind. The chirping vanished as expected, but was replaced with a slight vibration felt in the seat starting at 50-55 mph. I dropped the truck off at the driveline shop to get the driveshaft balanced. They put it on the balancer and called to say they couldn’t balance it, the indicator kept jumping around and wouldn’t stabilize. I asked them to reinstall it and came to pick get the truck. The guy who worked on it said that this was usually a u-joint problem. I asked what brand they used and pulled he out a Neapco u-joint box and said they use them exclusively and have never had any problems. I ordered Neapcos from RockAuto. Will replace the Moogs and see what happens. After they reinstalled the shaft I drove in the freeway and it acted exactly the same.
I was very careful when pressing out the old joints not to stress any of the yokes, applying pressure to the u-joint members at right angles to the cap being pressed out and not to the cap 180 degrees opposite. When installing the new joints, after inserting the clips (interior) I pressed all clips snug against the yoke. The joints all moved freely in all directions. Again, the shaft was replaced exactly as it came out.
Does anyone have any insight into what exactly would cause the indicator on a balancing machine not to stabilize?