Mustang Cobra IRS in an A-body

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Stacked360

Stacked360

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I have been toying with the idea of trying to make this work...my main problem is trying to figure out how wide I can have a rear end, be rotor to rotor or hub to hub. The stock A-body 8 3/4 is from my measurements almost exactly 57" hub to hub. The cobra suspension is apparently (from what I've been told) is 61" rotor to rotor. I plan on rolling the rear quarter wheel lips and other things, but I just can't seem to be able to picture what would happen should I swap that rear end into the duster. Anyone have any ideas? or heard of a similar case custom job?
 
I'm sort of worried it will end up looking funky with to much offset, not to mention hard to get wheels. I'm also a little worried if I put to much offset on the wheel, getting enough tire under the car without hitting the shock or spring might become on issue.
 
Well I said that because the stock A-body rear end is already too short for Dusters/Demons and IMO look weird straight from the factory. I don't think you'll have to use that much offset to center the tires in the wells.
 
Its going to be a street/handling car. I totally agree with you mope that the stock rear end "sucks" the tires into the wheel wells to much, I'm trying to find something that will handle like nuts, be strong enough to handle the 5.7L Hemi, have tires that are between 7.5-8" wide, and fit in the wheel wells without looking to small like the original rear end does, but doesn't rub on the wheel wells because of being to wide.
 
Another measurement to consider is offset from center. I dont know what differences will be there if any. If Chrysler set the engine off center and the differential on center , then Ford did just the opposite , you'll have a mess .
 
No sooner than the public got it's hands on Cobra IRS and discovered the shortcomings, the Mustang tuner shops started coming up with fixes for the handling. I'm not sure anyone ever found a real solution for axle breaking during drag race starts.

If you really like the looks of the Ford IRS, take a look at the MN12 (89 up T bird-Cougar and the Mark VIII Lincoln. The Super Coupe T bird and the Mk VIII also come with the same 8.8 (aluminum center section and all) 31 spline as the Cobra, and it's even possible the geometry might be better. Just be aware, with the possible exception of the Super Coupe, only the Mk VIII has the correct 5 on 4.5 bolt pattern from the factory.

It might be possible to weld the Ford subframe right into the A body and tie it to full length frame connectors making what is a full frame welded to the bottom of the A body. Narrowing the axles and moving the IRS cradle longitudinals in toward the centerline of the car to provide more wheel/tire room is very doable for someone not afraid to tackle this project in the first place. With all the various offsets used on different year Mustang wheels, you might find narrowing not necessary at all. Mating tubular axles to the Ford U-joints might be the answer the drag race axle breakage.

Another possible donor source for IRS is (and this might not set well in the stomach) is the premium lines from Datson and Toyota. I saw the bottom of a high end Lexis coupe in a junkyard with an IRS setup that looked like it had possibilities, differential and all.

I vaguely remember someone here, or on one of the other Mopar sites starting this very project (Ford IRS in an A body).
 
I've also looked into this for my 5.7L '67 Dart project.

I'm not sure of the strength of them, but i've read that the 1968-1982 Corvette rear end is 59.5".

Here's a '72 'vette rear upgraded with lateral links and mono-leaf spring...
72_Corvette_23.JPG

72_Corvette_22.JPG


Off topic...
I just picked up an 8.8 Ford Explorer solid axle with factory disc brakes, 3:73, and LSD for $240. It's 59.75" hub to hub. I even came with the e-brake cables and brake lines/brackets to the body. I figured i'd save $ for a RMS front K-member.
 
First off, please bear with me, I'm a big fan of all Makes of cars and IRS.

Here's a Mopar w/ Ford T-Bird IRS
http://blog.cardomain.com/2009/01/09/1966-dodge-dart-irs-project-journal/

I have a 65 Barracuda and have thought to drop in a Cobra IRS also. I also own a Cobra IRS with a chunk of floor pan still bolted to it. I've also dropped a Cobra IRS under my 66 Mustang. I'm not sure how much clearance you have under your car for tires. Considering the Cobra rear is 2" wider per side if you used the same wheel dimensions you have now but with that 2" extra backspacing you should be fine. The 66 Mustang rear end was 57.25" wide. I decided to use the 03 Cobra wheels, 17x9s and flare the fenders.
My first idea was to beef up the Cobra unit but swapping out the 8.8 3rd member for 9" section I was going to mod to bolt in the same way as the 8.8. But, the 9" housing is just too big and the pinion is off-set too much to keep the 3rd member centered and tranny lined up with the pinion yoke. Too many variables and more work for little gains.
Oh, and centerline of the pinion is offset 1/2" to the passenger side.
http://hubgarage.s3.amazonaws.com/photos/905142/quarter_flare_detail.jpg

http://hubgarage.s3.amazonaws.com/photos/905150/rear_flare_with_IRS_shot_detail.jpg

This guy took a Cobra IRS and custom built control arms and had half-shafts cut to size for his corvette. It ended up being 52" wide. I was worried about messing with the geometry of the setup so I decided not to go this route. The Corvette owner is a cool guy, answered a lot of my questions.
http://www.cardomain.com/ride/2659577

I know this isn't a Mopar but I have a thread on a Vintage Mustang site with some good info I gathered you might find interesting.
http://forums.vintage-mustang.com/showtopic.php?tid/1505776/post/2032153/hl/cobra+irs/fromsearch/1/

Here's another Mustanger who narrowed a Jaguar IRS to fit inder his car
http://dazed.home.bresnan.net/JaguarIRS1.html

This guy did a Lincoln Mark VIII into a Mustang
http://s308.photobucket.com/albums/kk355/stangtjk/?action=view&current=Img_0621.jpg

There are other options for IRS, you might be interested in.
This is a custom built IRS based off the T-bird IRS to fit in an MGB
RobFicalora-BE.jpg

I wanted to do something similar to this by modifying the Cobra IRS to mount into the factory 66 Mustang front leaf spring mounting points. Now that I have everything bolted in I might use my car as a jig to do this eventually.

Factory Five based off the T-bird
factory%20five%20irs.jpg





I love the outside-the-box thinking these guys use in their kits. Reminds me of remote control cars.
321IRS
321IRS.1
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Other ideas include newer 300, Charger, Challenger and even Viper IRS but they all seem way too wide. I believe the 300 IRS is 65" wide, and the bolt pattern is ever so slightly off from the 5x4.5 pattern.
 
Interesting.......curious to see what you come up with. All the ones suggested are gonna require cutting out part of the floor out, exhaust routing issues, and a bunch of headscratching. Consider a triangulated 4 link??
 
Another possible donor - Toyota Supras (and their related luxury cars, the Lexus SC300, SC400, Toyota Cressida) from 1987 and later are almost the exact same track width as an A-body. Josh Skinner on slantsix.org had some pictures of a third gen ('87-'92) Supra IRS that he was putting in an L-body, but it looked like it could make a good match for an A as well. Right bolt pattern and everything.
 
I've thought of using the IRS from a Chrysler conquest the measurements are the same you get the correct bolt pattern and disc brakes
 
Back in the day, when we wanted IRS for a front engine car, we went to Jaguar. The system all mounts to a sub frame that can be unbolted from the body with everything pretty much intact. The early versions (61-93) had inboard mounted rear disc brakes. The springs were mounted to the subframe.

The later version had the brakes out at the wheel. The springs mounted to the body.


Bolt pattern is 4½" on both except wire wheels with knock offs.

Model........................Track
E-Type Series 1 & 2.......50"
E-Type Series 3.............54"
S-Type........................54"
420.............................54"
Mark X.........................58"
420G...........................58"
XJ6 & XJ12 Series 1,2,3..58"
XJS.............................58"
Daimler DS420...............58"
 

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In the past and present alot of street rodders still use the Jaguar IRS because of its strength, gear selections and inboard brakes. I been tooling around with the Mercedes IRS which also has the strength and actually sits below its own subframe which rolls out on its cradle. My buddy put an LT1 330hp engine in his older BMW using its own BMW IRS and hasn't had problems.
I have the Mercedes IRS unit which is all aluminum and was told that the half shafts can be cut and balances for whatever usage.
 
lots of interesting topics lately. Awesome info and that vette is pretty sick a lot of time went into that car.
 
I was also thinking about using a jag IRS later down the line. I have a late 80s jag just sitting and figured she would be happy to give her life for some American muscle.
 

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