new edge rearend swap IRS/ stick axle

[blacksheep-1]

OK, I just finished this project. I found a guy in the "for sale" section named Mat that owns a Cobra that he wants to drag race. I, on the other hand own a 99 GT that I autocross and may occaisionally use for open track days. The deal is, he needs a stick axle due to the wheel hop accompanying the IRS and I need to go around corners, we decided to swap out. He has an IRS with under 50K miles on it, I had a stick axle with a rebuilt posi, 3.55 gears and new axles. My rear also had a set of Granatelli adjustable trailing arms and a Hotchkiss sway bar.
This is actually a very straightfoward swap since the IRS was designed to simply slide under the stock Mustang. The IRS also weighs an extra 80 pounds, this may not be so bad, even though it sucks for drag racing, in the road racer it will add weight to the rear of the car and help offset the nose weight that makes the car "push".
It would be nice to have had the cars side by side, that way if we found a problem we could simply use the part off of the other car. Mat lives about 1-1/2 hours away, and in fact we did need to make an extra trip for the IRS brackets that replace the quad shock mounts.


As you can see this is what the IRS looks like under the car.(this particular car has coil over springs) Raise the car up and securely support the chassis, chock the front tires and remove the rear wheels.
1.Unbolt the exhaust from the foward pipes at the rear of the transmission. Once you seperate them from each other you can slide them off of the other brackets and out from under the car.
2.Remove the 4 bolts on the drive shaft, the IRS shaft is a DIFFERENT LENGTH than the stick axle
3. Support the rearend on a floor jack or preferably, a transmission jack.
4.Unbolt the following:
A: The shock absorbers from inside the car under the trunk matting. THE SHOCKS ARE DIFFERENT SO KEEP THEM WITH THE IRS.
B: The forward mounting point of the subframe (located where the stick axle control arms bolt in) KEEP THE BOLTS WITH THE IRS
C: The rear mounting point of the subframe (located where the quad shocks mount) the brackets for the quad shocks ARE DIFFERENT .
D: Unbolt the brackets as well and keep them with the IRS.
E: Unbolt the hydraulic brake lines from the bulkhead connection located ON THE CHASSIS and keep them with the IRS do not unbolt them from the calipers!.
F: Remove the brake cables from the CHASSIS, and keep them with the IRS.
5. Take out the rear seats and remove the vehicle anti lock tubing from insdie the vehicle and slide it out through the hole in the floorboard.
6. Once all of that is done. carefully remove the IRS with the jack, do this slowly, in case you missed something.


7. As you lower the rear, the springs should fall out from under the car. the SPRINGS ARE ALSO NOT INTERCHANGEABLE so keep them with the IRS.
8. At this point, unless you screwed up really bad, the assembly should look something like this.



I cannot express how important it is to keep all of the related parts with the IRS, a lot of bolts are stepped, or different diameters. The shocks APPEAR to the same THEY'RE NOT! the stick axle shocks will not interchange with the IRS (the shocks can be bolted up from the IRS to the stick axle, but not visa versa, and the internal valving is different. The brake lines can be changed at the calipers, BUT, they are not really interchangeable, the brake lines can come loose because the banjo fitting is different even though the IRS brake lines can physically be bolted to the stick axle) the bottom line KEEP THE IRS PARTS WITH THE IRS, AND THE STICK AXLE PARTS WITH THE STICK AXLE!!

By now, any self respecting hot rodder should know how to pull out a stick axle, but here's some pointers.
1. Don't unbolt things seperately, there's no reason to make extra work for yourself, as an example do not unbolt the lower control arms from the axle, they're just going to be reattached later, instead unbolt them from the chassis only, same with the upper control arms.
2. Once you remove the quad shocks, take the brackets (and the bolts) with you, you will need them on the other car.
3. Now is a good time to replace any worn parts, especially on the IRS, since it is a major PITA to fix it once it is in the car.

That's really about it, just reverse the procadure for each vehicle for the reinstall. It's all only held in by about 10 bolts, 2 nuts and a couple of clips.

[KAILUAZ]

Nice write up! Now where can I find one for my coupe?!

[MiDiablo]

+1 for awesome write up!

[Frankie Figs]

Great write up but I have a question. Do you need to use the Cobra catback with the IRS? I would assume so because they're designed differently but I thought I'd ask.

[blacksheep-1]

Yes, you'll need to swap everything from the cat-backs. The IRS exhausts run under the rearend similar to a Corvette and there's no room over the top for a standard exhaust system.

[vertigyn]

Good write up - I didn't do anything like this when I did my swap! =)

Now go order Bruce's bushing kit over on SVTPerformance.com - great upgrade to get rid of all the rubber in th IRS to make it plant and handle better!

[3dglasses]

Nice writeup, now fix that body roll!!! That looks like a clean IRS...

[blacksheep-1]

That pic is back when I ran NASA class"D", which was basically a stock class.