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Old 09-05-2022, 06:43 PM   #1
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Join Date: Jan 2004
Location: Burke,VA
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IRS Swap explained in detail?

I've begun combing through several IRS threads but was hoping to find a 'Complete Guide to IRS Swap' sticky...

Basically I want to research and read all about what an IRS swap entails.

Can anyone provide helpful links that explain it in detail?

Then out the gate I have a very elementary 101 question...
Does an IRS swap require a willing Cobra donor (trade for SRA)?
If it's not possible to find a swap, can the IRS be purchased or built?

Appreciate any help or info!
2004 Black Mach 1
297.77 RWHP & 320.27 RWTQ

1/4 mile: 13.230 @ 106.43, 1.979 60'
1/8 mile: 8.568 @ 84.54, 1.979 60'

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Old 09-20-2022, 04:10 PM   #2
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Re: IRS Swap explained in detail?

How timely. I was literally coming here to ask if anyone wanted me to post up my IRS swap that I'll be starting on in the next 60-90 days. (This is subject to change and the completion of a few other projects first so it will probably be more like 180 days in reality).

There is no requirement to swap your live axle with an IRS from a Cobra donor. It is sometimes easier to do that however simply due to supply. The IRS units used to be quite plentiful as a TON of Cobra owners were swapping them out for a solid axle setups but that has cooled off. Many of the parts are obsolete from Ford so you can't simply buy the whole unit new from Ford (which would have been super expensive anyways).

My advice is to buy yourself a complete IRS unit, preferably from an 03-04 as those are the best units from the factory for a few reasons. If you end up with an earlier IRS, you can upgrade them as needed. If your car is stock and you end up with an earlier IRS, there are a few things you should probably do to it as the earlier IRS units just couldn't handle the power and usually ended up having issues/breaking. The 03/04 units had 31 spline axles and a factory diff brace. I believe the upper arms were also different but I'm not sure if they matter at all or if it was just a design revision?

If you have a complete IRS assembly with the brake lines and ABS sensors then it is a complete bolt in upgrade except for 1 thing. You either need to change the pinion flange on the IRS carrier (I would leave it since it is a beefier unit) or upgrade the flange at the end of your drive shaft to the larger Cobra unit (this is what I'd do/did). Other than that, total bolt in if you have a full assembly.
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