cobra IRS in fox swap

I am not sure there is any movement at all. I mean the center section is stationary to the car, meaning of the car moved up and down the tranny and pumpkin will move in the same plane thus not moving in relation to eachother. Am I wrong in this assumption?

There is not suppose to be any but the cobra has a lot of rubber in every fastening including the pumpkin which will give it some movement. All that rubber is one of the huge shortcomings of the stock IRS.

On a side note which springs are you guys running. Apparently I have the front cobra springs and not the rear IRS springs. Thought they looked a tad narrow but whatever. Looks like I need to source some rear springs. Any suggestions as to if I should look for some stock ones or go for some aftermarket.
Kevin

I really like the stance of your cars. Its not too low and you can make it over a speed bump. What springs are you guys running?
Kevin

Well this looks like a plan for me to you guys just drilled all the info i needed but how about picks of the under car maybe on a lift? i got a irs setup for 550 it has 4.56 gears, custome prototype bushings, and cradle stiffeners welded on to it

After talking to MM they suggested the H&R race spring. We will see how those work.... I will give an update once they are in.
Kevin

Every install instructions say to keep the pigtail of the spring in the same location. Without ever seeing one installed yet, where does the pigtail suppose to go for the spring orientation?
Kevin

Springs are on and the 2 inch drop seems perfect. I am in the process of doing the brake hardlines but I would like to knowwhat type of connector did you use to go from the hardline to the softline? I am using the double flare metric fittings but there doesn't seem to be an inverted flare on the female(cobra softline) side.
Kevin

Just wanted to share some pics of my progress.
I used a 1 3/8th holesaw to get into the framerail.


Here is a sucky closeup of how I just cut a corner off a bolt head and used the current nut that is welded in the framerail as a support to keep it spinning. I figure that way, the bolt is flush and not crooked or going through both sides of the framerail. You will see a couple pictures down that the nut is on the outside of the rearmost bracket.


Next is the trunk with all the holes.


Next is with the front bolted in.






With the H&R IRS race spring.


All 4 wheels on the ground... Have yet to move it around to see if the springs squat a tad more.




And the cleance with 245/45/17




he brake conversion isn't done yet so I cannot tell you how it rides yet... Need a little more time and money but I have most of the parts for that at least.
Kevin

Sorry, my garage is a disaster...
The stock driveshaft length works just fine. Even with my TKO600!
Kevin

Sicarius428, your swap looks great man!

I'm about to embark on the IRS swap myself. Me and a buddy are going to try and tackle it. I just finished up the front Cobra brakes a few weeks ago.







Gotta get those ^^ Ponies off.

So I found me a '03 IRS for $850 with 22K on it. And I've got a few questions for you.

1. What couplers/fittings did you use to connect the IRS softlines to the Fox hard brake lines?

2. What are the exact parts I need to mate the Fox driveshaft to the IRS pumpkin. (My IRS came without a flange) How would it work if I tried to hook up the fox drive shaft straight to the the IRS? Why is that not a good idea?

3. Is there any fabricating, cutting, or welding that needs to be done (besides the exhaust)?

4. Did you have to bend or re-flare the Fox hardlines to work with the IRS?

I know I'm forgetting some of the questions I was gonna ask, but this is a good start I guess. I'm getting a bit nervous that I won't be able to pull it off and have to run away with my tail between my legs.

Oh, and I'll be taking pics as I go for anyone who is interested/curious.

fox racer said:

Plus, the extra weight is over the rear wheels, so it helps with traction at little.

Click to expand...

once you get to the 300hp range, that extra weight isn't going to justify getting traction. i have had an 01 cobra pushing 329 hp at the wheels and on a rainy day in 3rd gear doing 70mph, if i hit the gas it would break loose and i could keep them spinning into 4th at about 120mph (that's what the speedo would read). it was scary but horribly fun...

85_SS_302_Coupe said:

Yeah, then if you've got a tubular K member/A arms, aluminum heads and fiberglass hood, trunk mount the battery...you might really be close to 50/50.

Click to expand...

yeah,, the handling in a fox with the irs and those mods would be rediculously good!! when i had my 01 cobra the handling with unbelievable. i had h & r sport springs, monroe sensa trac struts, and maximum motor sports caster camber plates and the ride was sooooooo smooth that i couldn't understand it because it was lowered 1.7"..

Sicarius428 said:

I found one on my local mustang forums. They pop up on ebay a bit but the shipping is pretty bad. Out of the box the Cobra IRS is pretty floppy. They used rubber at every joint which can give it some pretty bad wheel hop.... especially with the power that some of these terminators are running. For strength and simplicity they swap it out for a solid axle. I have weighed out both options of either going with the IRS or building up my solid with gears, 5 lug and brakes. Even so the IRS came out cheaper for me with the added perk of better handling and better weight distribution. I can always address the wheel hop issues later with replacing all the rubber but I never go to the drag strip anyways.
Kevin

Click to expand...

if you plan on going to the drag strip, you wouldn't want to get irs.. the wheel hop is bad. everytime i launched hard i thought my rear was going to fall out.. haha (i knew it wasn't, just a joke) so with an irs you just can't launch hard, you have to slip the clutch to be able to leave the line with traction and no wheel hop..

2000xp8 said:

They are so expensive to mess with, level 5 axles are like 2 grand if you need them.
High coolness factor, but i'd rather put the money into the rest of the handling setup.

And even beefed up with bushings and braces, they can still wheel hop, watch them run on drag radials at the track, looks like the wing is going to break off the trunk lid when wheel hopping.

Click to expand...

no matter what you do to them IRS's they will always get wheel hop if you launch them hard. i would only consider putting it in my car if it's a DD and want the ride quality. which is exactly what i'm looking for haha

Sicarius428 said:

Yeah... the Level 5 axles are pretty steep. Typically the stock axles are prone to fail because of all the slop from the factory bushings causing binding. Please understand aftermarket bushings aren't the answer for everything in the Cobra IRS... it does aleviate a lot of the issues with it though. If you check out svtp's marketplace, Bruce with the screen name of AC427cobra has built a full custom kit for the IRS using Delrin and AL. This kit also makes the diff solidly mounted in the cradle. I highly suggest reading up on the feedback and results to show the full potential of the IRS. Again.. for strait line you can't beat the old stick but the IRS has a lot more potential than its given credit for. Either way I'll find out soon.
Kevin

Click to expand...

exactly! put polyurethane bushings in the irs and you will solve a lot of the slop in the irs.. those rears are know for making a slight banging noise when putting it into reverse because those factory bushings wear quickly. so by putting in the poly's you will get much better traction and get rid of that noise

ryan218 said:

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

i always blamed it on the irs also... haha it made a nice drift car

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..

Click to expand...

If you plan on using it for drag racing - their is no amount of money you can put into this rear to fully get rid of the wheel hop.

If you plan on using it as a DD and drag racing once in a while - the irs is the best rear you can get. It's so much smoother on every bump, every road, every railroad track crossings are practically not their.. lol i am biased to the irs. i lived with that comfort for a long time and now that their is a post on this, i am considering doing it.. i have never even thought about it b4.. haha

Sicarius428 said:

Just wanted to share some pics of my progress.
I used a 1 3/8th holesaw to get into the framerail.
View attachment 291195

Here is a sucky closeup of how I just cut a corner off a bolt head and used the current nut that is welded in the framerail as a support to keep it spinning. I figure that way, the bolt is flush and not crooked or going through both sides of the framerail. You will see a couple pictures down that the nut is on the outside of the rearmost bracket.
View attachment 291197

Next is the trunk with all the holes.
View attachment 291199

Next is with the front bolted in.
View attachment 291201

View attachment 291203

View attachment 291205

With the H&R IRS race spring.
View attachment 291207

All 4 wheels on the ground... Have yet to move it around to see if the springs squat a tad more.
View attachment 291209

View attachment 291211

And the cleance with 245/45/17
View attachment 291213

View attachment 291215

he brake conversion isn't done yet so I cannot tell you how it rides yet... Need a little more time and money but I have most of the parts for that at least.
Kevin

Click to expand...

what springs did you put in? did you buy the cobra springs or the fox springs to use?? and same thing for the struts. are you buying it for the cobra or for the fox body?

Txstang347 Thank you for the kind words.
1. What couplers/fittings did you use to connect the IRS softlines to the Fox hard brake lines?

I still havn't gotten the car on the road yet... been broke and havn't found much time lately but to answer your question, I cut the stock hardline right at the end of the tunnel and put a double flare T on the end. From there I used a double flare on the T end and a bubble flare on the other end to connect to the stock cobra soft lines. I found the cheapest place to get the T was from ebay. Just make sure that all sides on the T fitting are double flared and you should be set. A lot of the fittings i found only had the inlet a double flare...

2. What are the exact parts I need to mate the Fox driveshaft to the IRS pumpkin. (My IRS came without a flange) How would it work if I tried to hook up the fox drive shaft straight to the the IRS? Why is that not a good idea?

You can pull the stock flange from your current 8.8 and slap it on the cobra pumpkin. Several people have done that just to save cost and time instead of looking endlessly for the correct flange to turn up. From 99-01 IRS, the stock driveshaft will just bolt up but 03/04 the flange is much larger is the only reason. My IRS came with the cobra flange still on the pumpkin so decided to to get the flange off a cobra driveshaft and use a precision 448( i believe) adapter flange. It adapts a 1330 stock fox driveshaft to a 1350 cobra drive shaft flange. I needed a new ujoint anyways so two birds with one stone... or that was my justification.

3. Is there any fabricating, cutting, or welding that needs to be done (besides the exhaust)?

The whole thing is pretty much drill and bolt in. You don't need to weld anything. Some I have seen weld the rear mounting brackets to the frame rail but that is a personal choice. I don't think its necessary. There is a far bit of cutting or banging in my case to get the rubber bumstops off the framerails right above the axle tubes. I used my grinder to cut whatever I could and pulled out a 5 lbs hammer and chisel and knocked off the spot welds. Wear goggles when doing this... It may not seem dirty but all sorts of junk comes falling down... not to mention that you are flailing a large hammer against metal.

4. Did you have to bend or re-flare the Fox hardlines to work with the IRS?

You pretty much toss everything after the tunnel. I followed what these guys did for the most part. IRS INTO FOX BODY
It looks like they cut further down the trans tunnel and made an extension... I didn't do that and just cut the line right after the tunnel. You will most likely have to remove the bracket where the softline attaches to the hardline too. I just drilled out the rivit.


Good luck to ya.

Snakebite01. For the rear springs you will have to use cobra IRS springs. The fox springs taper down at the bottom to sit on the mount. The cobra springs are the same size top to bottom. I used the H&R race springs. My IRS didn't come with springs... well it came with the front cobra springs but not the rear... hehe oops. I consulted Maximum Motorsports and that is what they suggested to go along with my 300 lbs front coilover kit... which has yet to install itself. If you do use the stock rear cobra springs, you may have to cut them because they were made for a much heavier car.
For the front, I would use the fox springs. The stock cobra springs are 600lbs springs I believe so it is a bit much. MM will sell just the rears if you need them. I think it costed me about 150 for mine... Unextected expense but its a hobby. Depending on what front springs you have already, I would give them a call and see what they suggest to balance out the rear.
Kevin

Sicarius428 said:

Txstang347 Thank you for the kind words.
1. What couplers/fittings did you use to connect the IRS softlines to the Fox hard brake lines?

I still havn't gotten the car on the road yet... been broke and havn't found much time lately but to answer your question, I cut the stock hardline right at the end of the tunnel and put a double flare T on the end. From there I used a double flare on the T end and a bubble flare on the other end to connect to the stock cobra soft lines. I found the cheapest place to get the T was from ebay. Just make sure that all sides on the T fitting are double flared and you should be set. A lot of the fittings i found only had the inlet a double flare...

2. What are the exact parts I need to mate the Fox driveshaft to the IRS pumpkin. (My IRS came without a flange) How would it work if I tried to hook up the fox drive shaft straight to the the IRS? Why is that not a good idea?

You can pull the stock flange from your current 8.8 and slap it on the cobra pumpkin. Several people have done that just to save cost and time instead of looking endlessly for the correct flange to turn up. From 99-01 the stock driveshaft will just bolt up but 03/04 the flange is much larger is the only reason. My IRS came with the cobra flange still on the pumpkin so decided to to get the flange off a cobra driveshaft and use a precision 448( i believe) adapter flange. It adapts a 1330 to a 1350 i think. I needed a new ujoint anyways.

3. Is there any fabricating, cutting, or welding that needs to be done (besides the exhaust)?

The whole thing is pretty much drill and bolt in. You don't need to weld anything. Some I have seen weld the rear mounting brackets to the frame rail but that is a personal choice. I don't think its necessary. There is a far bit of cutting or banging in my case to get the rubber bumstops off the framerails right above the axle housing. I used my grinder to cut whatever I could and pulled out a 5 lbs hammer and chisel and knocked off the spot welds. Wear goggles when doing this... It may not seem dirty but all sorts of junk comes falling down... not to mention that you are flailing a large hammer against metal.

4. Did you have to bend or re-flare the Fox hardlines to work with the IRS?

You pretty much toss everything after the tunnel. I followed what these guys did for the most part. IRS INTO FOX BODY
It looks like they cut further down the trans tunnel and made an extension... I didn't do that and just cut the line right after the tunnel.


Good luck to ya.

Snakebite01. For the rear springs you will have to use cobra IRS springs. The fox springs taper down at the bottom to sit on the mount. The cobra springs are the same size top to bottom. I used the H&R race springs. My IRS didn't come with springs... well it came with the front cobra springs but not the rear... hehe oops. I consulted Maximum Motorsports and that is what they suggested to go along with my 300 lbs front coilover kit... which has yet to install itself. If you do use the stock rear cobra springs, you may have to cut them because they were made for a much heavier car.
For the front, I would use the fox springs. The stock cobra springs are 600lbs springs I believe so it is a bit much. MM will sell just the rears if you need them. I think it costed me about 150 for mine... Unextected expense but its a hobby. Depending on what front springs you have already, I would give them a call and see what they suggest to balance out the rear.
Kevin

Click to expand...

thanks.. this is definitely something i wanna do to my fox in the future..

I sure hope it is worthwhile. I havn't heard anything but great praise about the swap so we will see. I just got the manual ebrake adjuster and I have to do the mod to the brake handle. From there I gotta replace my whole front suspension so it will be a little while. With xmas coming up, I gotta divert my funds a bit but I think the only thing I am missing are some caster camber plates... and time.
Kevin

Sicarius428 said:

I sure hope it is worthwhile. I havn't heard anything but great praise about the swap so we will see. I just got the manual ebrake adjuster and I have to do the mod to the brake handle. From there I gotta replace my whole front suspension so it will be a little while. With xmas coming up, I gotta divert my funds a bit but I think the only thing I am missing are some caster camber plates... and time.
Kevin

Click to expand...

yeah i here what your saying.. do you have any preference on cc plates?? i have always had maximum motorsports and i absolutely love them..

Sicarius428, thanks for all the info man. It's been a great help and it's helping me visualize it more. Although, most of this stuff is like greek to me at this point. I guess once I get in there and start to gut the car it will make way more sense.

Luckily I got my IRS almost complete, minus the cobra flange. And, I hear ya on being broke. This Cobra IRS/brake upgrade has cost me way more than I intended. The original plan was Dual piston GT brakes in front and 5 lug drums out back...lol.


1. What couplers/fittings did you use to connect the IRS softlines to the Fox hard brake lines?

I still havn't gotten the car on the road yet... been broke and havn't found much time lately but to answer your question, I cut the stock hardline right at the end of the tunnel and put a double flare T on the end. From there I used a double flare on the T end and a bubble flare on the other end to connect to the stock cobra soft lines. I found the cheapest place to get the T was from ebay. Just make sure that all sides on the T fitting are double flared and you should be set. A lot of the fittings i found only had the inlet a double flare...

Got any part #'s on the double flare T or bubble flare? The front driver's side Cobra brake line needed a 7828 weatherhead fitting to mate to the softline. Are there any of those issues with the rear '03 lines not mating up with the hardlines?

2. What are the exact parts I need to mate the Fox driveshaft to the IRS pumpkin. (My IRS came without a flange) How would it work if I tried to hook up the fox drive shaft straight to the the IRS? Why is that not a good idea?

You can pull the stock flange from your current 8.8 and slap it on the cobra pumpkin. Several people have done that just to save cost and time instead of looking endlessly for the correct flange to turn up. From 99-01 IRS, the stock driveshaft will just bolt up but 03/04 the flange is much larger is the only reason. My IRS came with the cobra flange still on the pumpkin so decided to to get the flange off a cobra driveshaft and use a precision 448( i believe) adapter flange. It adapts a 1330 stock fox driveshaft to a 1350 cobra drive shaft flange. I needed a new ujoint anyways so two birds with one stone... or that was my justification.

Have you connected the driveshaft to the IRS yet? If I understand you correctly you used a Cobra flange on the IRS side and the driveshaft side and used a "precision 448 adapter" to adapt the Fox 1330 driveshaft flange to the 1350 cobra driveshaft flange?

Oh and where did you find these parts by the way? Autozone employees look at me like I'm crazy when I ask for parts for this swap.

Is it possible to mate the current stock Fox driveshaft up to the 2003 IRS I have? Or is that only possible with 99/01's? Also, I found this online:

Irs Fox Body Mustang Loctite The Pinion Nut Photo

Was wondering if this would be a big deal because I have nothing on there at the moment to get a "previous preload measurement" from.



Thanks, again for the info man. Hope I'm not being a pest. I'd like to document as much as possible to make easier on the next guy. I need CC plates to get the front end aligned so I might just pick up those springs you used while I'm at it to drop the rear, although I do want to go with 18" wheels soon, so maybe I'll wait to install those first.

Joe
Austin, TX

Got any part #'s on the double flare T or bubble flare? The front driver's side Cobra brake line needed a 7828 weatherhead fitting to mate to the softline. Are there any of those issues with the rear '03 lines not mating up with the hardlines?
This is the fitting you need.
Smith Fastener Company - Union Tees
I belive that this is the Tee fitting I got... Might even be from the same vender.
http://cgi.ebay.com/ebaymotors/3-16...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

Have you connected the driveshaft to the IRS yet? If I understand you correctly you used a Cobra flange on the IRS side and the driveshaft side and used a "precision 448 adapter" to adapt the Fox 1330 driveshaft flange to the 1350 cobra driveshaft flange?

I do have my driveshaft hooked up.. Just not tightened since I have yet to do the ebrakes. I kept the stock flange on the pumpkin and found a 03/04 cobra driveshaft flange. To adapt it I used the Precision 448 u-joint to make them work together. The stock fox driveshaft flange is a bit smaller. Here is a link to it.

Precision Universal Joint 448 - Precision U-Joints - summitracing.com

Oh and where did you find these parts by the way? Autozone employees look at me like I'm crazy when I ask for parts for this swap.

Yeah, all the local parts stores were pretty much useless. I never tried napa... and I know they have a lot of fittings.

Is it possible to mate the current stock Fox driveshaft up to the 2003 IRS I have? Or is that only possible with 99/01's? Also, I found this online:

Irs Fox Body Mustang Loctite The Pinion Nut Photo

Was wondering if this would be a big deal because I have nothing on there at the moment to get a "previous preload measurement" from.

I used that article for the images. Especially when it came to the brake lines. In your situation I am not sure... You may want to call a local driveline shop and pick their brain a bit.

It is my pleasure to help you out. I think I gave all the right part numbers but please double check to make sure.
I am definately getting MM caster camber plates.... someday.
When you choose your wheels, be very cautious of the width. Anything wider than an 8inch with the sn95 backspacing is definately going to rub... 8inches might still rub. It's going to be close if I am guessing right. I have to wear out the current tires to justify even looking at wheels but the sn97 wheels as mentioned before fit a lot better with their offset. Just something to be mindful of.
Kevin

Sicarius428 said:

Got any part #'s on the double flare T or bubble flare? The front driver's side Cobra brake line needed a 7828 weatherhead fitting to mate to the softline. Are there any of those issues with the rear '03 lines not mating up with the hardlines?
This is the fitting you need.
Smith Fastener Company - Union Tees
I belive that this is the Tee fitting I got... Might even be from the same vender.
http://cgi.ebay.com/ebaymotors/3-16...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories

Have you connected the driveshaft to the IRS yet? If I understand you correctly you used a Cobra flange on the IRS side and the driveshaft side and used a "precision 448 adapter" to adapt the Fox 1330 driveshaft flange to the 1350 cobra driveshaft flange?

I do have my driveshaft hooked up.. Just not tightened since I have yet to do the ebrakes. I kept the stock flange on the pumpkin and found a 03/04 cobra driveshaft flange. To adapt it I used the Precision 448 u-joint to make them work together. The stock fox driveshaft flange is a bit smaller. Here is a link to it.

Precision Universal Joint 448 - Precision U-Joints - summitracing.com

Oh and where did you find these parts by the way? Autozone employees look at me like I'm crazy when I ask for parts for this swap.

Yeah, all the local parts stores were pretty much useless. I never tried napa... and I know they have a lot of fittings.

Is it possible to mate the current stock Fox driveshaft up to the 2003 IRS I have? Or is that only possible with 99/01's? Also, I found this online:

Irs Fox Body Mustang Loctite The Pinion Nut Photo

Was wondering if this would be a big deal because I have nothing on there at the moment to get a "previous preload measurement" from.

I used that article for the images. Especially when it came to the brake lines. In your situation I am not sure... You may want to call a local driveline shop and pick their brain a bit.

It is my pleasure to help you out. I think I gave all the right part numbers but please double check to make sure.
I am definately getting MM caster camber plates.... someday.
When you choose your wheels, be very cautious of the width. Anything wider than an 8inch with the sn95 backspacing is definately going to rub... 8inches might still rub. It's going to be close if I am guessing right. I have to wear out the current tires to justify even looking at wheels but the sn97 wheels as mentioned before fit a lot better with their offset. Just something to be mindful of.
Kevin

Click to expand...

what about wheel spacers?? would you be able to fit like a 9 with wheel spacers?

Unfortunately wheel spacers go the wrong way. The IRS is about 3 inches wider than the fox axle... Sorry I wasn't clear before. The clearance issue is with the body of the car not the wheel well.
Kevin