Chrysler has offered a special tool to remove the bushing with trans in car for years. Check out the FSM and if not in there it is in the Miller Special Tool catalog. A bushing installer is also shown.

Both removal and installation can be done with the extension housing bolted to the trans.

^^^ Sounds like a plan. when the time comes be sure & post the outcome.

went out and put a piece of wood on top of my floor jack and put it under the transmission and raised it up a little to see if it changed anything..same ole thing..seemed like it might have not been QUITE as bad but still there, i think it wasnt quite as bad because i had the trans picked up so it wasnt transmitting it quite as much through the trans mount..Oh well, wishful thinking i guess..I will try to do more this weekend..I dont have a lot of time between work and mowing the property and everything else..I wish one of you guys lived closer and could come by and check it out..
I guess this weekend i will try and remove the yoke from the driveshaft and put the yoke in the trans and see what happens..Then pull the pan and also see if i can see anything going on at the flexplate area..

so, has the "C" clips situation been addressed? all 8 installed on shaft joints?

You mean have they fallen off?

Installed they usually do not fall off, but some installers have failed to install them.

Seriously? wonder why? you would think they wouldnt get far before it all fell apart without the clips..

At some point, the factory started adding a big weight to the back of the tail shaft. I think there was one on an 82 Cordoba I used to own. I always assumed the weight was to eliminate some unwanted harmonics. It would be interesting to see what would happen if you bolted one of those onto the tail shaft.

I just cant figure out why its been fine the last 20 something years and all the sudden its got this vibration out of no where..

on 70s

I have one of those ready to be installed on my car. There are two kinds of those thought

Can you describe how it felt?

worse around 50 mph and up. it made pulsating vibration. i found it when I pulled the trans and noticed the cracked flex plate.

did it do it in neutral also? Did it rumble the whole car when it did it?

Today i pulled the driveshaft back out and fired it up on the jackstands and ran it again..It did NOT do the pulsating/phasing vibration with the driveshaft removed! I checked the shaft and u-joints over again and reinstalled it. I also decided to change the transmission mount. The old one fell out in 4 pieces when i removed the cross bar..Put it all back together and no luck, still does the vibration.. Unfortunately i am going to have to take a break from the car. I have spent the last 7 weekends working on it from sun up to late afternoon doing the front end rebuild and disk brake swap and now trying to figure this problem out. My body hurts and i have so many jobs around the house that im behind on now, This really sucks because when i got the front end and disk swap done, i was ready to do some driving with this car..now im stumped..

Well, this may not be as bad as i thought..as i said, i changed the trans mount and with it set up on jack stands, it still did it. ok, i decided to take it out for a ride and the first thing i noticed is that unless im REALLY looking for it, i didnt notice it..After driving around for an hour, im starting to think it has always been like this, but i didnt really notice it until the trans mount let go and then it was REALLY noticeable! Now, with the new mount, i really cant hear it like i was and can feel it just a little but really have to be looking for it.. I still need to figure it out but im not as worried as i was because i do believe its back to normal.

The vibration could made the mount failure! So it could be not fixed but absorved

so, if it DIDN'T pulsate without the shaft, the question comes up in my feeble mind, who balanced it, and was the shaft high speed balanced ? [higher than the normal truck shaft builder]
if you mentioned before this answer, i apologize for not remembering.
glad you discovered the broken mount.

& on that note I remember a somewhat prior post that alot of shops dont balance for high RPM (which is something I did not know), I had assumed if it was "balanced" that it was balanced (& all good).

We have a big driveshaft shop in nashville thats been around for YEARS and they are the ones that cut down the driveshaft and installed the u-joints and balanced it.. They are well known and used by lots of people so i just assumed it was done right, but i dont know..Why do most NOT high speed balance the shafts being that they DO indeed spin quite fast? Seems as though there is a lot of vibrations running around if thats the case..My next question is, could it still be a problem in the transmission and it doesnt show untill the driveshaft is installed?

Is there a high speed and low speed balance procedure for crankshafts?