[Nyt_Muves]

I have the opportunity to purchase the rear end out of a 99 COBRA. It has around 60K on it. It includes everything right down to the rear calipers and rotors. Supposedly it would be a direct bolt in and directly replace the setup I have. The only thing it is missing is the rear springs. I would have to buy those anyway to match it with the Eibach prokit I already have installed.

Is it a swap worth doing? Is it really worth the trouble? The setup will cost me $1000 and I will have to drive 2K miles to pick it up.

Would the gains be worth the trouble?

Any insight into this would be appreciated. Those of you with COBRAs, how do you like your IRS?

Again, any insight would be greatly appreciated.

[coolwaterblvd]

Nope stay away your stock rear will take more Hp than the IRS from the 99. As a matter of fact a lot of cobra owners are going to the solid axle even the 03-04 cobra owners with the stronger unit's are going with the solid axles in high HP applications and they are much cheaper to fix.

[reivaxtorres]

Originally Posted by Nyt_Muves

I have the opportunity to purchase the rear end out of a 99 COBRA. It has around 60K on it. It includes everything right down to the rear calipers and rotors. Supposedly it would be a direct bolt in and directly replace the setup I have. The only thing it is missing is the rear springs. I would have to buy those anyway to match it with the Eibach prokit I already have installed.

Is it a swap worth doing? Is it really worth the trouble? The setup will cost me $1000 and I will have to drive 2K miles to pick it up.

Would the gains be worth the trouble?

Any insight into this would be appreciated. Those of you with COBRAs, how do you like your IRS?

Again, any insight would be greatly appreciated.

this depends on what you are doing. i have an 04 cobra IRS sitting in the garage waiting to get installed in my 98gt. ive looked it over countless times, along with reading so many how-to articles on it, and yes, the 99/01 IRS is a direct swap into our cars WITH THE EXCEPTION of 4 holes you need to drill, 2 on each side. a few things to point out tho:
99/01 IRS is a direct swap into 94-04 GTs (94-98 have to drill 4 extra holes for the mounting bracket that will replace the quad shocks, 99+ GTs it will be a perfect swap as they already have these holes)
03/04 IRS units are much stronger than the 99/01 counterpart(but 94-98 still need those extra 4 holes). updgrades include:
-better bushings on everything
-stronger halfshafts
-31 spline axles (99/01 have 28 spline)
-pinion brace (non existant on 99/01, now included to help reduce wheel hop)
-came with blisten shocks from the factory
-3.55 gear ratios (compared to the 3.27 for the 99/01 units)(since i already upgraded my solid to the 3.55 gears, this was better for me also)
but, the 03/04 units require a few things to make them work, mainly being the driveshaft. the pinion flange on these is slightly different, so ur either going to get a special u-joint, swap the flanges, or get a custom driveshaft.

from what ive heard (and hope to experience by the beging of next month) the IRS will give you a much better ride and much better handling. if you are into drag racing, dont do it. if the car is just a daily driver, then its really not worth it to do the swap just to get a better ride quality. if you want to keep drivability but be able to handle some twisties, i would say go for it. the main bad thing you will hear about the IRS units is that the cobra guys are snapping the half shafts often, but those are the ones making good power (400+rwhp, slicks, 7k rpm launches, etc). since my car pretty much wont make that much power for a long while, i have no worries about that. i drift my car, and i plan to road race it also, so the IRS is justifiable for me. its not going to see drag time that often, and when it does its not going to be on slicks or even drag radials.
also, i got the complete (minus the calipers, which are the same as the GT ones) 04 unit with 20k miles SHIPPED for $1150 (IRS was in louisiana, im in california), if you arent too eager for it search around locally for it (or even ebay, or forums) and you might find it cheaper. from what ive seen, the 03/04 units are more expensive than the 99/01 units, and you shouldnt pay more for these. the 03/04 usually go for around $1000-$1200, so if i were you id look around.
oh yeah, dont forget that you will need a new catback too. mine came with the original exhaust too, but since i already have the magnaflows, i plan on just keeping mine and getting custom bent pipes to work with the IRS.
if you are going to buy the IRS (not swap for your live axle) do what i plan on doing and keep everything from your axle for a few months. try out the IRS, and if you dont like it swap the solid back in and sell the IRS, or if you fall in love with the IRS, sell ur solid later on. (or keep it for a future project)

[Nyt_Muves]

Originally Posted by reivaxtorres

this depends on what you are doing. i have an 04 cobra IRS sitting in the garage waiting to get installed in my 98gt. ive looked it over countless times, along with reading so many how-to articles on it, and yes, the 99/01 IRS is a direct swap into our cars WITH THE EXCEPTION of 4 holes you need to drill, 2 on each side. a few things to point out tho:
99/01 IRS is a direct swap into 94-04 GTs (94-98 have to drill 4 extra holes for the mounting bracket that will replace the quad shocks, 99+ GTs it will be a perfect swap as they already have these holes)
03/04 IRS units are much stronger than the 99/01 counterpart(but 94-98 still need those extra 4 holes). updgrades include:
-better bushings on everything
-stronger halfshafts
-31 spline axles (99/01 have 28 spline)
-pinion brace (non existant on 99/01, now included to help reduce wheel hop)
-came with blisten shocks from the factory
-3.55 gear ratios (compared to the 3.27 for the 99/01 units)(since i already upgraded my solid to the 3.55 gears, this was better for me also)
but, the 03/04 units require a few things to make them work, mainly being the driveshaft. the pinion flange on these is slightly different, so ur either going to get a special u-joint, swap the flanges, or get a custom driveshaft.

from what ive heard (and hope to experience by the beging of next month) the IRS will give you a much better ride and much better handling. if you are into drag racing, dont do it. if the car is just a daily driver, then its really not worth it to do the swap just to get a better ride quality. if you want to keep drivability but be able to handle some twisties, i would say go for it. the main bad thing you will hear about the IRS units is that the cobra guys are snapping the half shafts often, but those are the ones making good power (400+rwhp, slicks, 7k rpm launches, etc). since my car pretty much wont make that much power for a long while, i have no worries about that. i drift my car, and i plan to road race it also, so the IRS is justifiable for me. its not going to see drag time that often, and when it does its not going to be on slicks or even drag radials.
also, i got the complete (minus the calipers, which are the same as the GT ones) 04 unit with 20k miles SHIPPED for $1150 (IRS was in louisiana, im in california), if you arent too eager for it search around locally for it (or even ebay, or forums) and you might find it cheaper. from what ive seen, the 03/04 units are more expensive than the 99/01 units, and you shouldnt pay more for these. the 03/04 usually go for around $1000-$1200, so if i were you id look around.
oh yeah, dont forget that you will need a new catback too. mine came with the original exhaust too, but since i already have the magnaflows, i plan on just keeping mine and getting custom bent pipes to work with the IRS.
if you are going to buy the IRS (not swap for your live axle) do what i plan on doing and keep everything from your axle for a few months. try out the IRS, and if you dont like it swap the solid back in and sell the IRS, or if you fall in love with the IRS, sell ur solid later on. (or keep it for a future project)

That was VERY helpful. The guy selling this unit will not ship. He will only allow local pick-up. He's in Maryland, I am in AZ. This means that getting it will require real investment in time and money. So it would cost $1000 for the unit, plus 3-4 days drive for a round trip and probably $600 fuel for my pickup to go get it.

I love to play in the twisties, but for the most part this is just a weekend toy for me. I was more interested in the increased cornering capacity than the ride improvement. Most of the week the Mustang sits under a cover in the garage.

Sounds like I can find a better deal if I keep my eyes open, and that maybe its worth holding out for an 03-04 model...

By the way, when you do this, take good pics. No offense but I would rather learn through your experience then have to re-invent the wheel myself.

BTW, where did you get the rear end? Where would you try to find one if you were me?

[reivaxtorres]

Originally Posted by Nyt_Muves

That was VERY helpful. The guy selling this unit will not ship. He will only allow local pick-up. He's in Maryland, I am in AZ. This means that getting it will require real investment in time and money. So it would cost $1000 for the unit, plus 3-4 days drive for a round trip and probably $600 fuel for my pickup to go get it.

I love to play in the twisties, but for the most part this is just a weekend toy for me. I was more interested in the increased cornering capacity than the ride improvement. Most of the week the Mustang sits under a cover in the garage.

Sounds like I can find a better deal if I keep my eyes open, and that maybe its worth holding out for an 03-04 model...

By the way, when you do this, take good pics. No offense but I would rather learn through your experience then have to re-invent the wheel myself.

BTW, where did you get the rear end? Where would you try to find one if you were me?

yeah, for some reason i think i know which one you are talking about, its on ebay, right? (or maybe not, i think i saw one on there, looked pretty clean but the guy doesnt ship either, i think he said something about getting it for a classic mustang or something), and no, its really not worth it if you have to travel cross country to get it.
since ur more interested in the cornering abilities of the IRS, i would suggest you get it. most people will say that you can get the solid to perform with the IRS(both fixed up, of course. stock vs stock the IRS wins), but to do so you would greatly reduce the ride quality, and i mean greatly (think race-only).
and trust me, ill be taking plenty of pictures of the swap, and ill forward you the links i have found so far on the swap. it really does look pretty easy and straight forward, i think i have a link (on my work computer) of someone installing an 03 IRS into a 98 Cobra, which is pretty much the same as the 98GT.
as to where you can try looking for one, like i said i found mine on ebay after looking around locally, i tried all the mustang shops i knew of and i tried most of the mustang-specific junk yards around here too, apparently no one really has cobra parts lying around. i even went to several track days out here and asked around all the cobra guys if anyone had one, or knew someone, who had one for sale or trade. i did, however, find this thread where the guy lists that he has an 03 IRS unit for sale (along with various other mach1 and cobra parts) that you can check out, i read thru the thread on friday and it seems like it hasnt been sold thru the forum yet, so you could probably call him and ask if he has sold it yet:
Mach 1 and Cobra parts for sale - ModularFords.com
i googled the number he posted up and its actually out of the same city i live in (ontario, ca, which sucks cuz he's had his post up almost as long as i had been looking for the irs, which would have come in handy if i had found it earlier, would have saved a little time with the cross country shipping, tho i am pleased with the party i bought mine from, very helpful person).
since it seems like you were willing to drive to maryland for it, i assume you probably wouldnt have a problem driving to so cal for this one, seeing as to how you are closer. and if he still has it for sale, doesnt ship, and you cant make the trip for whatever reason, let me know and ill see what i can do to help you out with the shipping, maybe crate it up and ship it to you. tho who knows, a trip to cali might be a worthwhile one. and in case you arent too familiar with the area, ontario is about 30 minutes away from San Bernardino (to the east of us), 40 minutes away from LA (to the west), about a 3hr drive to vegas, and about 2 hrs to the mexican border. just to give you a reference...

[reivaxtorres]

here are some of the links i have, these are the ones i have been looking over continously for i dunno how long now, i think i almost have them memorized:

98 cobra:
1999 Cobra IRS Install
00 GT:
Chad's 2000 Mustang GT American Racer -- IRS Swap
Fox Body (all you need to read from here is the section about drilling the holes for the brackets, good pics are the ones towards the bottom of the page, last 2 before the last one, the rest is useless):
IRS INTO FOX BODY
cobra to GT (pay attention to the driveshaft part):
03 Cobra IRS Swap

also, one thing i forgot to mention earlier, this swap will be ADDING weight to your car. from what ive read, the 99/01 unit will add around 70-75lbs, the 03/04 unit will add 80-85lbs. the good part about this, however, is that it will 1) help even out the weight distribution of the car; 2) reduce unsprung weight by about 125lbs (tho from what ive heard this might be overstated)

[kscoyote]

Originally Posted by reivaxtorres

here are some of the links i have, these are the ones i have been looking over continously for i dunno how long now, i think i almost have them memorized:

98 cobra:
1999 Cobra IRS Install
00 GT:
Chad's 2000 Mustang GT American Racer -- IRS Swap
Fox Body (all you need to read from here is the section about drilling the holes for the brackets, good pics are the ones towards the bottom of the page, last 2 before the last one, the rest is useless):
IRS INTO FOX BODY
cobra to GT (pay attention to the driveshaft part):
03 Cobra IRS Swap

also, one thing i forgot to mention earlier, this swap will be ADDING weight to your car. from what ive read, the 99/01 unit will add around 70-75lbs, the 03/04 unit will add 80-85lbs. the good part about this, however, is that it will 1) help even out the weight distribution of the car; 2) reduce unsprung weight by about 125lbs (tho from what ive heard this might be overstated)

Right, but if you send the unit to Kenny Brown's shop, they can knock 70 lbs off the unit.

[reivaxtorres]

Originally Posted by kscoyote

Right, but if you send the unit to Kenny Brown's shop, they can knock 70 lbs off the unit.

hadnt heard about that yet, but i bet it wont be cheap. besides, like i said, it will help improve the weight distribution, which will further help the cars ability to take corners. besides, there are plenty of other ways to shave off the added weight

[my02gt]

I just bought my IRS from ebay for $900 with only 4k miles on it along with a couple of extras including the stock exhaust. I spent alot of time on ebay looking and waiting for the right one to come along. Patience is worth it.

[kscoyote]

Originally Posted by my02gt

I just bought my IRS from ebay for $900 with only 4k miles on it along with a couple of extras including the stock exhaust. I spent alot of time on ebay looking and waiting for the right one to come along. Patience is worth it.

you probably outbid me on that one . ..

[kscoyote]

Originally Posted by reivaxtorres

hadnt heard about that yet, but i bet it wont be cheap. besides, like i said, it will help improve the weight distribution, which will further help the cars ability to take corners. besides, there are plenty of other ways to shave off the added weight

It costs around $1200 (at least it used to) - tubular control arms, revised geometry, hard mounts to the chassis, etc.,

[reivaxtorres]

ok, so i finally installed the 04 IRS on saturday! truth be told, it was a really, really simple swap. everything is exactly as all the writeups have said. it took me about 8 hours total, but that is because i ran into a few problems. in all honesty, i probably would have finished it in about 3-4 hours working by myself in my driveway with simple hand tools.

Nyt_Muves, i know you asked me to take pictures so you can see what is involved in doing the swap, but like i said just follow the other guides and you should be set. a few corrections to what i had previously stated tho:

1) on the passanger side mounting bracket (the one that replaces the quad shock), you will need to do a little modification to make that bracket fit aside from drilling those 2 holes. it involved lowering the gas tank a little and taking a hammer to flatten out some of the sheet metal there so you can place the bracket smoothly on the frame.

2) i had stated before that you would need to get the cobra rear caliper mounting bracket in order to get it to clear the thicker rotor...not 100% true. it will fit, but BARELY. for the added security, you can go ahead and either get the cobra spec one or shave this one down, but like i said its not needed.


also, to make your life a little easier, spray some wd-40 on the exhaust hangers. otherwise you will be trying to get them off.
you only need 2 jack stands and 1 jack, but i would suggest you get 4 jack stands and 2 jacks, it makes everything easier.

right now my car has the stock IRS rear with the stock springs and it rides great. its so much smoother than the front now, and although i havent pushed it yet, it feels like its more stable in the turns and it seems like it lost a lot of body roll. this coming up weekend i will be installing the cobra springs/control arms in the front so i will update you with the results of that soon.

[Nyt_Muves]

Originally Posted by reivaxtorres

ok, so i finally installed the 04 IRS on saturday! truth be told, it was a really, really simple swap. everything is exactly as all the writeups have said. it took me about 8 hours total, but that is because i ran into a few problems. in all honesty, i probably would have finished it in about 3-4 hours working by myself in my driveway with simple hand tools.

Nyt_Muves, i know you asked me to take pictures so you can see what is involved in doing the swap, but like i said just follow the other guides and you should be set. a few corrections to what i had previously stated tho:

1) on the passanger side mounting bracket (the one that replaces the quad shock), you will need to do a little modification to make that bracket fit aside from drilling those 2 holes. it involved lowering the gas tank a little and taking a hammer to flatten out some of the sheet metal there so you can place the bracket smoothly on the frame.

2) i had stated before that you would need to get the cobra rear caliper mounting bracket in order to get it to clear the thicker rotor...not 100% true. it will fit, but BARELY. for the added security, you can go ahead and either get the cobra spec one or shave this one down, but like i said its not needed.


also, to make your life a little easier, spray some wd-40 on the exhaust hangers. otherwise you will be trying to get them off.
you only need 2 jack stands and 1 jack, but i would suggest you get 4 jack stands and 2 jacks, it makes everything easier.

right now my car has the stock IRS rear with the stock springs and it rides great. its so much smoother than the front now, and although i havent pushed it yet, it feels like its more stable in the turns and it seems like it lost a lot of body roll. this coming up weekend i will be installing the cobra springs/control arms in the front so i will update you with the results of that soon.

I just found an 04 rear in Cali. Going to pick it up once I get out of the hospital. I would LOVE to talk to you before I attempt this. Do I need any welding to make this work?

They are including everything right down to the calipers and rotors. What else do I need to round up to make this function?

If I PM you my cellphone, would you be willing to share your experience with me?

[reivaxtorres]

Originally Posted by Nyt_Muves

I just found an 04 rear in Cali. Going to pick it up once I get out of the hospital. I would LOVE to talk to you before I attempt this. Do I need any welding to make this work?

They are including everything right down to the calipers and rotors. What else do I need to round up to make this function?

If I PM you my cellphone, would you be willing to share your experience with me?

sure thing, i can PM you my cell also if you like. where in cali is the IRS?
as for the welding...you dont need it, but i will end up doing it. you will have a choice of either drilling 2 holes on each side (that go thru the frame and into the trunk) or welding the two brackets on. right now on mine it doesnt have either, but it does have some IRS subframe brackets welded on already (bought it like that) so thats helping out a little.
short list of what you will need...
03/04 rear driveshaft flange (ford ~$25-$30, ill get my invoice for the part # in the morning)
Precision 448 u-joint (ebay, $26)
cobra exhaust (came with the IRS)
cobra shocks/springs(came with IRS)
cobra brake lines (should come with your IRS, i made my SS lines work)
14mm Subframe bolts and nuts (Maximum motorsports - $26....you will need these to get rid of the "thud/clunk", ford used the wrong bolts, 12mm, for the front of the subframe when they should have used the 14mm ones. for the rear ones, the GT 12mm ones will work...get them off the lower control arms)

and i think thats pretty much it. if you need pictures or anything like that just let me know and ill see what i can get for you

[Nyt_Muves]

Originally Posted by reivaxtorres

sure thing, i can PM you my cell also if you like. where in cali is the IRS?
as for the welding...you dont need it, but i will end up doing it. you will have a choice of either drilling 2 holes on each side (that go thru the frame and into the trunk) or welding the two brackets on. right now on mine it doesnt have either, but it does have some IRS subframe brackets welded on already (bought it like that) so thats helping out a little.
short list of what you will need...
03/04 rear driveshaft flange (ford ~$25-$30, ill get my invoice for the part # in the morning)
Precision 448 u-joint (ebay, $26)
cobra exhaust (came with the IRS)
cobra shocks/springs(came with IRS)
cobra brake lines (should come with your IRS, i made my SS lines work)
14mm Subframe bolts and nuts (Maximum motorsports - $26....you will need these to get rid of the "thud/clunk", ford used the wrong bolts, 12mm, for the front of the subframe when they should have used the 14mm ones. for the rear ones, the GT 12mm ones will work...get them off the lower control arms)

and i think thats pretty much it. if you need pictures or anything like that just let me know and ill see what i can get for you

San Pedro

Its out of an 04