IRS Swap

http://www.stangpro.com/html/articles/irs.htm

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Johnny,
Many have said that the difference between the IRS and a fully built solid rear are minimal.

You've already got most of the components done for the built solid rear, so why not just continue?

Stang|ess said:

I have an 04 GT, and want to swap in an 01 Cobra IRS, but have a few questions. Is this a direct swap? I know that with the 03/04 IRS setups, you need to do something with the driveshaft yolks, but isn't an issue with the 99-01 setups.

I read from bennybell? that you need to drill new holes, and weld new nuts? Can someone elaborate more on that please. What's needed besides the shocks, and springs. I wont have tailpipes so a new catback isn't an issue. Thanks!

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The only time you will need to drill holes in your frame rails is if you have a 94-98 SN95, or a Fox or other vintage stang; then it's just four holes per rail.

99-01 IRS's have inferior components (shocks/spring rates, bushings, tie rod ends, etc etc) - don't be tempted by the cheaper price, get an 03/04 unit!

As far as drive shaft mating goes on an 03/04 you can either A) swap the pinion flange from the rear ends, or B) swap the driveshaft pinion centering yoke off the driveshafts (the thing on the very end with for holes).

Exhaust wise - the mounting spots for the mufflers are different, so you WILL need some custom work to get dumps to work, plus I really wouldn't want to run dumps as the differential gets quite hot to begin with, having more heat down there would just make you burn up your clutch backs a lot faster.

Shocks and springs should come with whatever IRS you buy, and if they don't - go with Bilstein shocks, and whatever springs you have in the front to match in the back.

Stang|ess said:

$500 for a complete 01 setup save for the shocks and springs (I can get oem ones from my friend till I can buy aftermarket ones) and brakes is too good to pass up. if I do manage to find an 03/04 setup, shipping would kill me.

I'm going with roush side exhaust so would I still have to move my mufflers? didn't think the IRS reaches that far back into the car.

sanford, I have stuff (MM lcas, eaton posi, moser 31 spline axles) but its not installed yet. I called henry last november but forgot to call him back . its still nothing compared to your setup, and nothing compared to a "crappy" 01 irs setup.


so an 01 would be a direct bolt on?

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If you do that roush setup make sure you buy the one for cobra with IRS, because GT side exhaust will not work. Also, keep that eaton Posi and put it in the IRS, upgrade diff is always good AND if you do go with 99-01 IRS, pickup a set of used 03/04 halfshafts (they are 31 spline, and can handle 600whp pretty easily).

Stang|ess said:

I'm actually going to modify my current exhaust to mate up with the roush tips .

99 cobra has 28 spline half shafts and the 01+ has 31 spline. would a gt posi work okay with cobra half shafts?

I was thinking about upgrading some bushings before putting it on, just not sure which to buy.

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Yes, the diffs are the same - as long as the spline count is the same. For bushings look at Maximum Motorsports and no where else! Get subframe bushings, diff bushings (urethane or aluminum), and if you have the cash control arm bushings.