last week I found this rectangular piece of rubber sitting under the rear of my 96 Deville and so I jacked up the rear and found that there are bushings between the body and rear end and that the metal parts of the bushings is completely shot. So I called the dealer and they stated that they are called insulator bushings, 4 total, 2 upper and 2 lower.
Does this sound familiar to anyone and does anyone have any clue as to how to change them. All I see is a 15mm bolt dead center but There has to be more to it.
These seem like something very common but easily unnoticed as the car still rides excellent lol

 

Ok just to renew this, These are called rear insulator bushings, 2 upper, and 2 lower.
These bushings are located near the coilspring on the drive side and the passenger side.
The lower bushings are held in place by 1 single 4.25" 15mm bolt that goes up from underneath.
Total labor is about 1.5Hrs max
Part numbers. OEM Ac-Delco
Upper isulator 3538757
Lower insulator 25678602
Here is how to change these bushings. jack up the rear of the car by the factory jack points, support with jackstands.
Starting with 1 side remove the bolt in the center of the bushing and the lower bushing will come off. Then pull down between the body and the rear suspension, (You will most likely have to disconnect the abs plug from the back of the bearing, and pop the wire out of the wire holder so it will not get pinched or pulled).
When you pry down you will be able to pick up the upper bushing which sets into the upper suspension under the body. Pick up the upper bushing and pull it out through the rear between the body and the rear suspension.
To install the upper it is the opposite of the removal.
Now once the new bushing is in place you can release the pry tool.
Next you will have to take a jack and jack up the rear suspension towards the body enough to get the bolt started.
Put the bolt through the center of the lower bushing and then thread the bolt in about 5 threads but do not tighten the bolt yet, as it will help to make the other side easier.
Repeat the same procedure on the other side but once the bolt is threaded you can now tighten the bolts down to 18-22ft lbs.
Voila the ride quality improves and no more noise or sway in the rear over bumps.
I will post pics tomorrow of overall job.
Hope maybe this might help someone else who needed it like I did.
Dont know If this can be a sticky

 

HI I'm doing the insulators on my 92 Eldorado and following your useful notes.
However after I remove the 115mm bolts the lower insulators come away ok, but I cannot pull down between the body and the rear suspension, it will not move at all and let me slide out the insulators. I've removed the bolts on both sides, but I cannot get the suspension to separate from the body. I've tried pushing up on the body but it just pulls the suspension up with it and lifts the whloe car off the stands,
Are there any other bolts I'm missing?