Thunderbird IRS - Ford Muscle Forums : Ford Muscle Cars Tech Forum
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post #1 of 8 (permalink) Old 07-21-2006, 07:54 AM Thread Starter
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Thunderbird IRS

I have been looking for some information on TBird IRS. I didn't even think to look here! I guess my brains asleep. I want measurements of the 89-97 Thunderbird IRS. These are on the SC's and V8's with 4 wheel disc brakes. What I want to know is the axle width from wheel mounting face of the rotor to the other one. I "think" it is about 59" but I need to know for sure. I also want measurements of the subframe that mounts the whole thing under the rear. Heck I can't even find pictures of the IRS. I read about a guy modifing one to fit into his 66 Mustang. I have been unable to contact him and the posting was a few years old. I want to see how much work it will be to make it fit in my car.

If no one knows, where is a good place to get this kind of info? Just goto a salvage yard with a tape?

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post #2 of 8 (permalink) Old 07-21-2006, 09:32 AM
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Thunderbird IRS

Seems like the TBird IRS would be awesome for a restomod. I wish I could help, but even though mine is a 5.0 car, it has drums out back.
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post #3 of 8 (permalink) Old 07-21-2006, 12:15 PM Thread Starter
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Thunderbird IRS

If you keep the HP in a streetable range and don't drag race the IRS would be a great add on to a classic Mustang or Falcon. I know the SC's have it. Most all of the 4 wheel disc V8's do. I still have the Cobra IRS to check out. Cobra owners keep swapping them out for solid axles because 600+hp causes wheel hop. And there are Explorers too. But I thought the Thunderbird would be the best one to start with. There are lots of them.
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post #4 of 8 (permalink) Old 08-01-2006, 07:22 PM
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Thunderbird IRS

Look around on the forums on or, you should be able to find some pictures there, maybe dimensions too.

The whole assembly is very heavy and bulky, and also has 5 on 4.25" bolt pattern, in case that's an issue. It can be converted to 5 on 4.5" various ways, those forums will have posts about that as well.

Ed N.

89 Mustang GT, "old school" street / track day project
66 Thunderbird Town Hardtop 390 4-V, comfy cruiser
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post #5 of 8 (permalink) Old 08-08-2006, 03:59 PM
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post #6 of 8 (permalink) Old 08-09-2006, 07:21 PM Thread Starter
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Thunderbird IRS

Yes the bolt pattern can be converted. And the IRS is I believe about 75lbs. heavier than a live axle. But the rear of a Falcon is light so the extra weight would improve ride and handling. And thanks for the article it was excellent. I have read up on the Cobra IRS into a 66/67 Mustang. I fits with special frame brackets. I have a feeling the TBird will be to wide. I'm going to track one down at a salvage yard and do the leg work. Thanks guys for your help!
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post #7 of 8 (permalink) Old 09-05-2006, 08:38 AM Thread Starter
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Thunderbird IRS

For anyone interested. The Thunderbird IRS is to wide. It was hard to measure in the position is was in but it looked to be at least 62" maybe a little more. It could be done but I don't have the skills to shorten something like that plus I'm sure It would require notching the frame rails. My Falcon is 58" so a good bit of engineering would be needed. Also the Cobra IRS is too wide. It will fit but would require fender flares for an extra 1.5" on each side. Thanks DVS Restorations for your help on the Cobra IRS measurements. Explorers are integrated into the frame so I didn't even bother to measurement one. There are after market kits available but I was hoping to do this for a lot less than $8000. Kits run from $8000-$10,000. Unless I win the lottery it looks like I will be using my straight axle.

Thank you one and all for your help,
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post #8 of 8 (permalink) Old 01-24-2016, 05:24 PM
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Re: Thunderbird IRS

I am in the process of installing this system in my 1070 mustang convertible. There are some modifications to fit in because of where the gas tank sits. The tank will need to be modified as well as the rear end carriage. The good news is the the width is only about 1/2 inch wider which in the big picture is nothing.
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