Ok I want to start out by saying that I know there is another thread that shows how to do this. But that one has a bunch of false information and it is lacking measurements and a few shortcuts. Now secondly. If their is another thread with this information I'm sorry I haven't seen it before. now let's begin! One last thing make sure you remove your trunk carpet before anything. You will see why later.

Parts list:
N-body-
sub frame
sway bar
All 6 trading arms
Parking brake cable
 Rear struts
And knuckles with all brake components.

To start you will need to remove all of your old suspension components and dispose of them. Then cut the exhaust back far enough to get out of your way Once that is done begin by lifting the subframe up to the frame rails and get an idea of what part of the spare tire well will need to be "adjusted" once you figure it out  just beat the amount you need to allow the subframe to sit of on the frame rails. It's not much at all and once the subframe is installed you can beat the spare tire well back out and utilize it.

Some people cut theirs completely out and if you have no use for it than that works too!

Now that that is taken car of remove the subframe and get your tape measure out, you will now mark where the holes need to be in the frame rail to mount the subframe.

You will be measure from this point, Which is the cross brace between the two frame rails. Measure from the very from of it.

So your first hole on the passenger side will need to be at 6 1/8".

 

Now go to the passenger side, measuring from the same point on the opposite side of the car your front hole on this side will be at 6 3/8".

 
Now that you have your holes marked use the appropriate size drill bit and drill those two holes.

Get a drill bit long enough to go through the frame rails and through the bottom of the trunk. You'll see why in a bit. Now that you have those two holes drilled through the frame rail and the bottom of the trunk, lift the sub frame up and line the two holes up according. Now mark the position of the other two holes.

(remember to always use a punch in the center of your mark to keep the bit from moving around) now drill those two holes. Again through the frame rail and floor of the trunk.

Once they are drilled go to the trunk and cut a square out around the holes on one side and repeat that on the other, and it should look like this when your done.

 
There are two reasons for doing this one is it simply makes it easier to put the nuts on the bolts instead of fishing them through a hole in the frame rail, and you will need to make a place for these two pieces of reed steele after you make them.

The reason for making these is to increase the clamping strength of the subframe so it's grabbing more than just the thin frame rail.

its easy to make these, on the drivers side just cut a piece to a length that will fit in the hole you cut, lay it in the hole and go from underneath and mark where your holes need to be on the piece of steele. Drill the holes and your done with that side.

Now on the passenger side it's the same process except you will have to cut a notch in it to clear the bolt that comes through for the gas filler neck. Now the frame rails have a bit of an arch in them so once you tighten the subframe down these will bend to the shape of the rails. That's fine!

 

So now that the steele is in the hole and everything has been drilled put the subframe back up and line up all the holes, run the bolts through the bottom and screw the nuts on the trunk side ( this keeps.the threads from being exposed to the outside for easy removal if need be) you'll most likely need some help with this part.

Now that your subframe is installed put the new e-brake cable in and all the rest of the suspension components all bolt right up.

mount the brake line bracket here: (3 1/2" on both sides)

 
And use stock grand am GT rear brake lines, now your done!

If you would like you can weld the pieces of the trunk back it. But you'll never know the holes are their once you put the carpet back in.

 

Now doing this swap will cause you to have two different bill patters so I would recommend doing the N-body front swap as well and here is the link to that:
http://www.j-body.org/forums/read.php?f=3&i=99830&t=99830
 
I'm currently working on a coil over setup for the nbody suspension on the jbody so I will keep you posted!

Hope this helps!

nice write up! maybe one day ill do this but as of right now, its not a priority.

in your opinion... how much weight does the IRS add vs the stock beam?



RIP silver car. You will be missed.

Thanks!
And I would say it adds almost none, the knuckles and calipers weigh absolutely nothing. They only thing that is remotely heaheavy is the subframe. But the handling is way to good to pass it up!

Do you think I could do this to my 1993?
I HATE the rear end on this thing! Has anybody seen it? There's a sway bar, but it doesn't even bolt to the body! It just runs along the bottom of the beam. Kinda dumb if you ask me, but I suppose they had their reasons...

No, this will not work on a 2nd gen without major fab work, the dimensions are too far off.

A trailing beam axle is a big sway bar itself. Adding a sway bar to the bottom (just like pretty much every other trailing beam axle out there) is the best way for the factory to do it.