cobra IRS in fox swap

Prime Lord · Nov 24, 2007

Be sure to get a writeup when you do it. I've looked at the ones I could find online and they're sketchy at best. I'm thinking about doing this, but I really want some more info on the install. If I'm understanding correctly, the mounting brackets are part of the original install and its easiest if you get them with the axle? Everything else on my current axle is already 5-lug so it would just be a rear end swap for me.

393, if you don't mind me asking, how much did it set you back?

ryan218 · Nov 24, 2007

Mustang78 said:
i dont see how people are finding the 03-04 cobra IRS units, i've never even seen one advertised...i can get ahold of the lincoln mark VIII and thunderbird IRS though, but i hear it's worse for some reason. And a guy at the 4I BBQ in Arlington had supercoupe IRS under his 86GT

i hated the IRS in my SC....it didn't hook for **** ....i blame it on the IRS

a guy with a blue GT hatch has a IRS in his fox..and someone said a while ago that Ram360 has one?

look them up..

93 LX · Nov 24, 2007

here is a pretty good write up.

http://www.mouthbreather.net/IRSSWAP.HTML

Allen

68FBJJZ109 · Nov 25, 2007

I just finished putting a IRS unit in my fox, got it off Ebay for 550... waiting for springs to come in. I had to cut to stock ones so i could get the car on the ground and move it around, so as of now the tires are resting on the fender wells. The write up from mouth breather is good i sued that to show my buddy what we needed to do before we started. You can't see it in the picture but it did kick the tires out about an half an inch or so. hopefully I'll have it driving by this weekend and i can chime in on what the difference is.

393windsor · Nov 30, 2007

Prime Lord said:
Be sure to get a writeup when you do it. I've looked at the ones I could find online and they're sketchy at best. I'm thinking about doing this, but I really want some more info on the install. If I'm understanding correctly, the mounting brackets are part of the original install and its easiest if you get them with the axle? Everything else on my current axle is already 5-lug so it would just be a rear end swap for me.

393, if you don't mind me asking, how much did it set you back?

68FBJJZ109 said he paid 550.... wow I paid 1000 shipping included. I guess if you look long and hard enough you can get it that cheap. Shipping really sucks if you have to pay for it. As others say get the 03-04 they are better units. The guy I bought it from said he is going to an auction soon to get two more 03 cobras to part out he will have it on eBay soon. His eBay name is yasell2006. Happy hunting!

393windsor · Nov 30, 2007

68FBJJZ109 what wheel are you using, wheel to wheel looks really wide. I know there is a difference in track width with the irs inch and half or something like that, for that reason there is a certain backspacing to use.

68FBJJZ109 · Dec 1, 2007

There 17x9 with 24mm of backspacing. They come right to the outside edge of the fender lip. Also the IRS is all buttoned up, Night and Day difference. I took a friend of mine who has a Lincoln MK 8, and he was very impressed with the ride quality and how it handled.

393windsor · Dec 1, 2007

68FBJJZ109 said:
There 17x9 with 24mm of backspacing. They come right to the outside edge of the fender lip. Also the IRS is all buttoned up, Night and Day difference. I took a friend of mine who has a Lincoln MK 8, and he was very impressed with the ride quality and how it handled.

Is the backspacing that your using from your solid setup. I'm sure that there is a backspacing that can be used to put the wheels back behind the fender so that tire will not come in contact with the fender. You said you had to cut the springs so you can install it. Were they to tall? What spring did you end up using? You say that it is a night and day difference, would you say it rides better than an sn95? I know that a 03-04 cobra has kind of a stiff ride thats why I'm asking.

68FBJJZ109 · Dec 1, 2007

I Thought i read some where that was the correct BS, because on the fox 8.8 they tucked in under the lip five when i converted the car to five lug. I cut my fox springs so i could use them to get the car on the ground and move it out of the garage the lower perch section of the spring is much narrower then the IRS one, thats why i had to cut them. I used the Stock 03 04 Cobra springs because I figured performance once would be to stiff for a car which weighs some 700 pounds less, and i did want to run into clearance issues since the tires already stick out so far. I have never rid in a sn95, only fox's. So i can't say. I can say I am very impressed with the IRS for the two days i drove it around.

Sicarius428 · Jun 3, 2008

Sorry to bring this back from the dead but where did you guys find the brakeline Tee. I think i ordered one of the inverted flange tees but I just wanted to see just in case I got the wrong one. None of the parts stores around here have a clue as to what I needed. Other than that The brackets are mounted and the cradle fits! I opened up the front lower control arm holes from a 12mm to a 9/16 which fits perfectly with the 03/04 cobra 14mm bushing. I figure it would tightened it up a tad. You can get the grade 8 bolts at osh. For the rear I used a 1 3/16 holesaw to punch holes through the trunk sheetmetal so I can drop the nuts and washers into the framerail. Another thing I did that might be helpful for anybody else that is doing this is the rear most hole you have to drill is right above the stock quadshock nut that is welded inside the ramerail. I used a hacksaw and cut off a corner of a grade 8 bolt and washer and used the nut that is welded to the inside of the framerail to brace the bolt while i tightened the nut on the bracket side. It came out really clean and flush to the framerail. I have seen a lot of people either drill strait through both sides of the framerail or the bolt is really crooked and not flush fitting(not very strong imo). If you do decide to drill through both sides of the framerail I would suggest putting some sort of spacer in there. That dead space is basically allowing either the bolt to crush the framerail when you torque down to it or allow flex. I always try to opt for the shortest bolt to do the job but thats just me.
Kevin

SVT32VDOHC · Jun 4, 2008

Use 17X8 05+ wheels. They have a +45mm offset vs. 94-04 17X8 which as +30mm offset. You can also buy 17X9 Bullits from American Muscle that have 05+ offset +45mm....but they still look like the 94-04 Bullits wheels.

Sicarius428 · Jun 4, 2008

Thank you for the info on the wheels. For now I have 2k GT 17x8 (wheels with new tires) which are going to have to work for now. Whole suspension/cobra brake conversion has pretty much broke me. Fortunately the rears are only 245/45/17 so I am praying that they will work with little to no work on the fender. I will mock them up and see what the range is before I put the springs in(waiting on some poly isolators). Other than the ebrake cables which need to be routed and the hardlines I think I am pretty much set.
Kevin

Mustang5L5 · Jun 4, 2008

I missed out on picking up an IRS for $600

I'm sure another one will come around.

Question though...how you guys routing the tailpipes? Like the Cobras?

Sicarius428 · Jun 4, 2008

I got a stock cobra catback for 60 bucks. It will have to be shortened a couple inches on each side right before the muffler but that is the way to do it. On the cobra catback the inlet and outlet are on the same side(towards the middle of the car) unlike the typical mustang exhaust which they are at opposing corners.
Kevin

bstrd86 · Jun 4, 2008

Mustang5L5 said:
I missed out on picking up an IRS for $600

I'm sure another one will come around.

Question though...how you guys routing the tailpipes? Like the Cobras?

I have the stock '03-'04 exhaust that I cut the mufflers out & welded SLP loudmouths in. I also polished the ends of the pipes to try to replicate the stock exhaust look.

Still not finished yet.

SVT32VDOHC · Jun 5, 2008

Sicarius428 said:
Thank you for the info on the wheels. For now I have 2k GT 17x8 (wheels with new tires) which are going to have to work for now. Whole suspension/cobra brake conversion has pretty much broke me. Fortunately the rears are only 245/45/17 so I am praying that they will work with little to no work on the fender. I will mock them up and see what the range is before I put the springs in(waiting on some poly isolators). Other than the ebrake cables which need to be routed and the hardlines I think I am pretty much set.
Kevin

Your welcome!! The 99-04 Bullit wheels that are 17X8, will fit just fine. They will be just inside the quarter, and I mean JUST inside. I have the 2001 GT solid axle in my notch and that is how they sat. The 17X8 05+ wheels are inside 15mm more. And the 17X9 05+ wheels are sitting right out at the edge like the 99-04 17X8's were, but, because of the extra 15mm offset, that extra 1 inch of width is all under the car, making it look really good. Let me share some pics with you.

17X9 05+ 45mm offset

Same

View attachment 315479

Compare these.
Driver side is 17X8 +45mm offset
Passenger side is 17X8 +30mm offset. Sits in and more backspacing under car. Also, pay attention to where the wheel sits, not the tire because the 05+ wheels have the silly 235-55's.

Hard to tell on the last two pics, but the difference is huge.

BTW...I rolled my quarters before I did body and paint work. I think it was necessary. I also welded bump stops on the frame rails. I have hit those about 3 times over the past 300-400 miles. Not bad really. Mostly over railroad tracks, or bumps under hard acceleration. If I didn't have those, I prolly would have touched the tire to the quarter panel on the very inside..

Mustang5L5 · Jun 5, 2008

Will the Fox D/S work? I have an AL driveshaft i'd like to keep.

Sicarius428 · Jun 5, 2008

SVT... damnit now I really want a notch...

Yup. The fox DS works. Only thing is if you get the 03/04 irs, you will have to either find the rear driveshaft flang off a cobra and get a precision 448(i think) u joint adapter. It goes from 1310 to a 1330 u joint. I believe Bstrd86 used one off an explorer but I am unsure what size ujoint is used. You can pull the flange off the irs pumpkin and swap it with the current solid you have is the other option. The 99-02 irs bolt right up to your stock driveshaft flange... but you should go with the 03/04 unit instead.
Kevin

SVT32VDOHC · Jun 6, 2008

I know you were asking about his IRS stuff...I took my 2001 shaft to a place around here, and they made an entire new one, but a tad shorter. They charged me 275 bucks....man I regret that, because I might not have needed it. I couldn't put the driveshaft in on my hoist....I couldn't even get the shorter on in on the hoist. I had to set the car on the ground, and jack up the rear end to get the new shorter one in. I wonder if the stocker would fit. Too late now, I don't even want to try it. I am better off with the new on anyways, because it has new U joints, new yoke, and it is shorter. I don't want the thing slamming into the trans causing damage.

Sicarius428 · Jun 6, 2008

Ideally there shouldn't much if any movement on the drivshaft. Granted there is a lot of rubber in the stock IRS setup but I cannot imagine the Driveshaft needing more than 1/4 inch of forward to back movement. I am in a bit of a different boat since I have a TKO 600. I am still using the stock DS from my T5 but I think the TKO is a bit longer than the T5. I guess I will find out soon.
Kevin

cobra IRS in fox swap

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