Vibration issue 85 300 SD
 

I also have a bad vibration issue at above 50mph under load coasting or in neutral pretty much disappears from all searchs I did on this subject and under car inspection when I lift up on driveshaft right at rear of trans I have at least 1/4" of up and down movement my flex joints look good front and back car has 265 to 300,000 on it I am thinking it is either the u joint or the center driveshaft carrier which I do not see either? Is the center carrier under the heat shield midway from front to back? I am hoping that is what is causing the vibration and is a fairly simple fix. I find this site very helpful with keeping this 30 yr. Old car on the road.

1/4" up - down sounds excessive... I'd pull ds and inspect the yoke nut...

When I had vibration at that speed, it was the centre bearing. On one of my cars, I "inspected" it by poking my small camera through an opening just behind the front flex disk and taking a few pics.

I am sure vstech is right - doubt there should be any movement there. Get it checked out properly. A failure can be disastrous.

https://dl.dropboxusercontent.com/u/...%20bearing.jpg

I solved my very bad vibration issue after having driveshaft off 2 times. I put new center bearing and holder on, new flex discs, one center bushing, a used driveshaft with a new u-joint installed by me which I tack welded in to keep in place. Total cost

1.center bearing + holder $14
2.flex discs $100
3.u-joint. $14
4.used driveshaft with vibration damper $40
5.center bushing $11
Total cost approx. $180 not counting at least 12 hrs. Of my labor it was a real learning experience like anything you could do it quicker 2nd time around. I think if did it over again I would not worry about the u-joint if it has a notched feeling in it as they are held fairly straight and I do not think that would give you vibration issues. It was a pita to put the u-joint in. Anyway now at 85 mph. my gear shift selector is quiet and I can hear the radio ounce more. It is an important fix as you do not want that shaft ripping lose at 80mph which is what this 85 300 SD likes to cruise at.