IRS rear swap in a fox?

bditty50 · Dec 20, 2006

I have a 89 coupe with all the MM 3 link,panhard, and torque arm setup. I'm looking into swapping a IRS 99-04 cobra rearend in my car. I think all the problems with these rearends are gone considering the cobras can run them fine with the right parts(bushings,Level 5 halfshafts, etc.. I was wondering if anybody has done one in a fox and how it turned out and how it handles. Also any regrets or problems?

Mustang5L5 · Dec 20, 2006

Nope, but having spent more then enough hours under 03+ Cobra's messing around with the IRS, i would love to get my hands on one to put in my Fox.

Downside is the weight, but i guess it will help achieve almost 50/50 weight on a Fox Mustang with some nose weight reduction

bditty50 · Dec 20, 2006

Yeah the weight distribution is so much better. I think the IRS with the right parts is awesome. They sell carriers that handles 750+ hp without braces, level 5 axles 1000hp, and urethane bushings. The weight is 75 pounds over a solid axles I mean with all the parts from my MM panhard, torque arm its not that much weight those parts are heavy. So what do you think about the IRS? I think a diff brace,bushings, and a diff cooler for open track are the must of mods for them.

wythors · Dec 20, 2006

Either MM&FF or 5.0 had an article on this swap in the last few months. It was done at www.bradscustomauto.com in Seattle on a car belonging to one of the techs there.

From their "Our Crew" page:

"Brian owns a Fox body Mustang currently undergoing a conversion to a race car. Mods includes a complete Kenny Brown system using front module and an IRS rear module."

bob331T76 · Dec 21, 2006

what dont you like about your setup?? I have the same and my bro has the IRS and it doesnt hook for S#$%....butthe ride is 100% better, you dont feel every little bump lol

bditty50 · Dec 21, 2006

I like the MM setup up I just want something better. An Irs is 100 percent better. I want the ride quality and more sureness on turns then I have now and I think the IRS is the answer.

bditty50 · Dec 21, 2006

Besides with the right parts you can make a IRS hook pretty hard. I mean my friend has close to 1000hp with his 03 now and hooks awesome.

MikeC · Dec 21, 2006

Go for the 03 -04 IRS if you do it. They come with the IRS brace, 31 splines, better half-shafts, and 3.55 gears.

jrichker · Dec 21, 2006

See http://www.mouthbreather.net/IRSSWAP.HTML for the how to do the IRS swap into your fox body Mustang.

bob331T76 · Dec 21, 2006

sell your car and buy an 03 lol

bditty50 · Dec 21, 2006

Anybody know how an IRS feels in a foxbody? It should be easy to find a 03-04 irs with all the people swapping to solid axles.

85_SS_302_Coupe · Dec 21, 2006

There's a guy on this forum who has the swap on his car....wasn't long ago he posted about it. I think it was a white coupe....

I really would love to do this on my car, since i'm all for handling before drag racing. Plus, there's something that's just badass about a little negative camber on all 4 wheels on a 20 year old car.

bditty50 · Dec 21, 2006

Yeah I can't wait to get started on it. I just hope it isn't super complicated. Also I hope I don't have regrets after doing it and getting rid of my solid axle.

85_SS_302_Coupe · Dec 21, 2006

bditty50 said:
Yeah I can't wait to get started on it. I just hope it isn't super complicated. Also I hope I don't have regrets after doing it and getting rid of my solid axle.

Just keep in mind that the brakes are going to need a major overhaul including the master cylinder and all that, as well as the exhaust being completely different from the mufflers back if you run with tailpipes.

bditty50 · Dec 22, 2006

I dont care about the exhaust really, not a huge deal. The brakes I shouldn't have to change much because I already have a new master cylinder and rear disc brakes.

85_SS_302_Coupe · Dec 22, 2006

bditty50 said:
I dont care about the exhaust really, not a huge deal. The brakes I shouldn't have to change much because I already have a new master cylinder and rear disc brakes.

Well you should be on the right track then....i assume you've done a 5 lug conversion then? If not this would be a great time to knock that out as well. The exhaust isn't a major deal, you just have to run tailpipes like the Cobras have.

bditty50 · Dec 22, 2006

NO, I don't have a five lug conversion but, that is one of the things I'm going to do. I just have the new master cylinder with rear discs and slotted rotors. Actually I want to get a MM tubular Kmember and control arms and do a full coilover and five lug conversion with this. Also I want to sell the Lentech AOD and get a t56. So the joke about buying the 03 cobra is going to be close to reality when I have the whole drivetrain lol. What kind of bushings should I run on the IRS? I just want to do the bushings first so I don't break halfshafts and gradually upgrade along the way.

bditty50 · Dec 22, 2006

Besides my tailpipes barely get up over my MM parts anyway. MM didn't even know if it was possible for me to run tailpipes.

bditty50 · Dec 22, 2006

I'd still like to talk to someone that has done a swap or ridden in a fox with an IRS. I wanna know how good they can pull on a turn and still have stablility. I know the highspeed stability is much better too. My ride quality is very good now in my coupe with the MM parts. I can't imagine with an IRS rear.

85_SS_302_Coupe · Dec 22, 2006

Well, i don't want to discourage you, but remember that solid axle isn't as bad for handling as it used to be, especially with all the goodies that MM and Griggs have. Those Griggs GR40 setups are insane, and usually pull well over 1g in the corners. I figure if IRS was that much better, and since it's pretty much a bolt in affair, why wouldn't everyone be doing it?

Well, that answer is sort of a loaded question, because it's actually in the rules that they can't change the design of the stock suspension...but still you get where i'm coming from. The fact is that the goods are out there to make a solid axle car out handle high priced German cars with double A arm suspensions...that says a lot.

Now, whether that means your IRS won't handle better than what you have now is anyone's guess. I would assume that it will, but i would also look into beefing up the whole rear end too. I still have yet to see an IRS car hook good at the track on slicks without wheel hopping like crazy.

IRS rear swap in a fox?

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