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post #1 of 24 Old March 28th, 2017, 02:49 PM Thread Starter
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Considering IRS swap

I know there are hundreds of threads all over the internet detailing pros and cons, and step-by-step guides, but this thread isn't that. I have a couple questions that I haven't been able to find the answers too.

I know for the most part it's a direct swap but there are a couple additional pieces needed.

1. My GT would need different exhaust to accommodate the IRS. Could I swap the GT exhaust for the Cobra exhaust if I were to find someone wanting a SRA swap?
2. The drive shaft needs a special adapter to connect the GT driveshaft to the Cobra dif. What is that part? Link? Part number?
3. I have read the Cobra rear brakes would have to stay with the Cobra and I would have to keep my GT brakes. Why is that? If I got SS brake lines would I be able to keep the Cobra brakes?
4. I currently have lowering springs. Would I be able to keep them or would have to use the Cobra's springs?
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post #2 of 24 Old March 28th, 2017, 03:54 PM
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I'll answer that I can
1. The catbacks should swap over just fine, I have an IRS catback behind my parents house, that is just sitting, as I was planning an IRS style exhaust on my 03 SRA but never got around to it
2. The lengths are a bit different, look up cobra 4R70W conversions and you should be able to find out the length needed. The only difference in length between going 4R70W(auto) to T-56 vs. GT 5-speed to T-56 not accounted for here, is the yoke, but that swaps right over and does not need to be accounted for as far as I know. Basically you need to know the difference in length
3. Not really sure here, people put cobra rears on the SRA all the time, so no idea why they wouldn't swap. More than likely it is an issue of the person with the IRS not wanting to lose the nicer rears.
4. You will need new lowering springs that match the IRS in the rear, and also most likely will need different shocks, IIRC the mounts are bigger for IRS, and the bolt hole is larger due to this. You also will want to look into a FTBR bushing kit for the IRS.

Hope this helped!

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post #3 of 24 Old March 28th, 2017, 04:06 PM
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A Moog 448 U-joint is what you need to connect your driveshaft to the IRS flange.
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post #4 of 24 Old March 29th, 2017, 11:02 AM
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I've done an IRS swap and couldn't be happier, if the funds are there I would highly recommend a FTBR kit before you put it in and swap out your fuel filter.

1. My GT would need different exhaust to accommodate the IRS. Could I swap the GT exhaust for the Cobra exhaust if I were to find someone wanting a SRA swap? Yes it bolts right to where the Gts come off
2. The drive shaft needs a special adapter to connect the GT driveshaft to the Cobra dif. What is that part? Link? Part number? No it doesn't if you swap the pinion flange from the cobra with the one that was in your GT it will work without an issue, that's what I did fits perfectly
3. I have read the Cobra rear brakes would have to stay with the Cobra and I would have to keep my GT brakes. Why is that? If I got SS brake lines would I be able to keep the Cobra brakes? Doesn't matter the cobra has the exact same rear calipers you do its just positioned higher up to accommodate the larger rotors
4. I currently have lowering springs. Would I be able to keep them or would have to use the Cobra's springs? Your going to need IRS springs

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post #5 of 24 Old March 29th, 2017, 11:48 AM Thread Starter
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Thanks for all the info! This is something I really want to do, but I don't know if I would be able to afford the bushing kit right off the bat. I think the best option would be to find someone who wants a SRA and do the swap in a weekend. It's a DD and my only car so I couldn't leave the IRS off of the car while I wait for funds to do the bushing kit.

I could buy an IRS and wait till I can get the bushing kit, install it into my car, then sell my SRA, but, even though SRA's are highly sought after, they don't command as much as IRS's. Even though I know I could sell it quick. I have a friend who has a 99 Thunderbird and he wants my rear end. No pun intended!
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post #6 of 24 Old March 29th, 2017, 12:07 PM
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Originally Posted by dexdiman View Post
Thanks for all the info! This is something I really want to do, but I don't know if I would be able to afford the bushing kit right off the bat. I think the best option would be to find someone who wants a SRA and do the swap in a weekend. It's a DD and my only car so I couldn't leave the IRS off of the car while I wait for funds to do the bushing kit.

I could buy an IRS and wait till I can get the bushing kit, install it into my car, then sell my SRA, but, even though SRA's are highly sought after, they don't command as much as IRS's. Even though I know I could sell it quick. I have a friend who has a 99 Thunderbird and he wants my rear end. No pun intended!
Thats exactly what I did, I lucked out i found a guy with a termi so I hopped on that 31 spline axel deal, I even got a spare axel on the side. I drove on my IRS for a couple of years then I finally bit down and bought the kit, very worth it.

When swapping dont forget to remove the pinion snubber the SRA set up needs that and the IRS wont go in if its there. Other than its actually really straight forward.

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post #7 of 24 Old March 29th, 2017, 12:34 PM Thread Starter
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Thats exactly what I did, I lucked out i found a guy with a termi so I hopped on that 31 spline axel deal, I even got a spare axel on the side. I drove on my IRS for a couple of years then I finally bit down and bought the kit, very worth it.

When swapping dont forget to remove the pinion snubber the SRA set up needs that and the IRS wont go in if its there. Other than its actually really straight forward.
Sweet. I'm going to finish up my front end then seriously start looking into this. I don't want to put any more money into my back end since I am going this route. Hopefully I can do it this summer.
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post #8 of 24 Old March 29th, 2017, 01:47 PM
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Sweet. I'm going to finish up my front end then seriously start looking into this. I don't want to put any more money into my back end since I am going this route. Hopefully I can do it this summer.
what are you running upfront?

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post #9 of 24 Old March 29th, 2017, 02:34 PM
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All this talk of IRS swaps has me itching to do it on my car. But I would insist that every single item FTBR has to offer be installed. And a Torsen T2R as well. And MM coilovers. But before all that I want to do a T56 Magnum swap.

Anybody want to loan me some money? About $7000 ought to do it.
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post #10 of 24 Old March 29th, 2017, 03:12 PM
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Originally Posted by MG2V View Post
All this talk of IRS swaps has me itching to do it on my car. But I would insist that every single item FTBR has to offer be installed. And a Torsen T2R as well. And MM coilovers. But before all that I want to do a T56 Magnum swap.

Anybody want to loan me some money? About $7000 ought to do it.
I looked into the T56 only problem I have with that tranny is 5th and 6th are overdrive, you can get pretty stout tr3650 with a taller 1st and shorter 5th for around the same price of making a t56 fit and work and the t56.

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post #11 of 24 Old March 29th, 2017, 03:43 PM
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I agree, a TR3650 is all I would need. But a T56 is what I want. And the wide ratio version (2.97 1st, .50 6th) has nice gearing for an N/A 2v with 4.10's or 4.30's. Good performance in 1st through 4th, and decent fuel economy in 6th.

But I digress. This isn't my hypothetical build thread
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post #12 of 24 Old March 29th, 2017, 03:54 PM
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I agree, a TR3650 is all I would need. But a T56 is what I want. And the wide ratio version (2.97 1st, .50 6th) has nice gearing for an N/A 2v with 4.10's or 4.30's. Good performance in 1st through 4th, and decent fuel economy in 6th.

But I digress. This isn't my hypothetical build thread
Pro-Force Pro-X - 700 ft/lbs - estimated 1000 hp - $3,125.00
- This is an "updated" TR3650 with a CUSTOM GEAR SET
- The ratios are: 2.90, 1.91, 1.37. 1.00 and fifth gear will be either 0.53 or 0.58
- Custom fifth gear ratios are: (0.63 discontinued) and 0.69
- The input shaft with this gear set has 26 splines and requires a 26 spline clutch
- Billet Bronze fork pads for gears 1-4
- Cryogen Tempered 3-4 Shift Fork
- "Gorilla" 1-2 Shift Fork

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post #13 of 24 Old March 29th, 2017, 04:13 PM
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I really wanted to do the swap, until I realized I wouldnt be happy without the bushing kit, and thats a lot of money
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post #14 of 24 Old March 29th, 2017, 04:32 PM
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I really wanted to do the swap, until I realized I wouldnt be happy without the bushing kit, and thats a lot of money
Wasn't that bad without it. Wheel hop was cured with some r888s

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post #15 of 24 Old March 29th, 2017, 05:00 PM
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Quote:
Originally Posted by MineralGreyGT View Post
Pro-Force Pro-X - 700 ft/lbs - estimated 1000 hp - $3,125.00
- This is an "updated" TR3650 with a CUSTOM GEAR SET
- The ratios are: 2.90, 1.91, 1.37. 1.00 and fifth gear will be either 0.53 or 0.58
- Custom fifth gear ratios are: (0.63 discontinued) and 0.69
- The input shaft with this gear set has 26 splines and requires a 26 spline clutch
- Billet Bronze fork pads for gears 1-4
- Cryogen Tempered 3-4 Shift Fork
- "Gorilla" 1-2 Shift Fork

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That's a nice transmission, I'm sure, but I'm still sold on the Magnum. Especially since the prices are practically identical.
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post #16 of 24 Old March 29th, 2017, 05:13 PM Thread Starter
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Quote:
Originally Posted by MineralGreyGT View Post
what are you running upfront?
When I bought the car all it had suspension wise was Eibach Sportline springs. Since then I have installed:
03 Cobra steering rack with aluminum bushings
MM solid steering shaft
Bilstein HD struts
Moog tie rods
All new bushings

All I need to is bring the roll center back into spec and she will handle like a sports car.

Here's the build thread if you or anyone might have any input on that - https://www.moddedmustangs.com/forums...t-project.html.

Quote:
Originally Posted by MG2V View Post
All this talk of IRS swaps has me itching to do it on my car. But I would insist that every single item FTBR has to offer be installed. And a Torsen T2R as well. And MM coilovers. But before all that I want to do a T56 Magnum swap.

Anybody want to loan me some money? About $7000 ought to do it.
I will be doing the FTBR bushing kit, just not at the time of the swap. Going from an SRA to an IRS will be a big improvement then adding on the bushing kit will make it even better.

---------- Post added at 01:13 PM ---------- Previous post was at 01:09 PM ----------

Quote:
Originally Posted by maxgst View Post
I really wanted to do the swap, until I realized I wouldnt be happy without the bushing kit, and thats a lot of money
Yeah to much for me right now, but later, that will diffidently happen.

Quote:
Originally Posted by MineralGreyGT View Post
Wasn't that bad without it. Wheel hop was cured with some r888s

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R888's? are those tires?
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post #17 of 24 Old March 29th, 2017, 06:15 PM
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R888's? are those tires?
yes sir Toyo R888
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post #18 of 24 Old March 29th, 2017, 09:47 PM
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I believe the drive shaft will bolt right up on 99-01 IRS units, atleast mine did. Went and bought the pinion flange, and ended up being exactly what was already on the 01 IRS i picked up.

E brake cables can be used too, but you will have to take the ratcheting mechanism apart in the car, then hook cables to calipers, then re assemble the e brake handle while adjusting for the extra cable needed for the IRS. or just swap to cobra e brake cables lol


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post #19 of 24 Old March 29th, 2017, 10:42 PM
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I believe the drive shaft will bolt right up on 99-01 IRS units, atleast mine did. Went and bought the pinion flange, and ended up being exactly what was already on the 01 IRS i picked up.

E brake cables can be used too, but you will have to take the ratcheting mechanism apart in the car, then hook cables to calipers, then re assemble the e brake handle while adjusting for the extra cable needed for the IRS. or just swap to cobra e brake cables lol
Not sure on the early IRS but for 03-04 you definitely need the GT flange. As for the calipers you don't need to do anything, they are the same. Only thing you need to do is if you still have the stock name lines, you have to bend them for cleaner that's it.

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post #20 of 24 Old March 30th, 2017, 12:08 AM
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If you have an 03/04 IRS, it would be better to get a hybrid u-joint like the one I mentioned above. The 1350 pinion flange on an 03/04 IRS is larger and stronger than a 1330 flange found on a GT. One is better off keeping that stronger flange, and adapting the driveshaft to work. 99/01 IRS used 1330 flanges.
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