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Discussion Starter #1
03 Cobra rear complete laying on the floor to go into a 99> GT.

Anything that could be installed/beefed up while system was out of the car that would be harder once installed?

Anything misc. or little things that need to be addressed?

Exhaust, brakes, and springs are of my concern off top of my head.

Thanks

(And yes, this is for open track/autoX use mainly. Minimal street driving/drag racing. )
 

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At the very least I would rebuild the differential with a new set of clutches. And while you are at it, use the alternating steel/friction plate method. If that rear end spent a decent amount of time behind an '03 cobra, the clutches will probably need attention.
 

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Do whatever gear change you think you might ever need to do BEFORE you put it in the car. And track down TennGT, he just did this a month ago.
 

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Discussion Starter #5
Thanks guys....... I was thinking these things, but have never dealt with an IRS before and didnt fully understand what to look for.
 

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Check the discussions on IRS differentials overheating and spewing gear lube out the vent hose that's near the top of the pumpkin. I've had all kinds of problems with that on my 99 Cobra both with 4.10 gears and 3.73 gears. May be why Ford doesn't install any gears bigger than 3.55?? Suggestions are lengthening the hose and/or installing a catch can so lube can get back into the diff. I've always run excellent rear lube, either RedLine MTL or Amsoil synthetic and still have the problem on extended highway drives and on the track. Design defect big time.
 

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Irish1 said:
Check the discussions on IRS differentials overheating and spewing gear lube out the vent hose that's near the top of the pumpkin. I've had all kinds of problems with that on my 99 Cobra both with 4.10 gears and 3.73 gears. May be why Ford doesn't install any gears bigger than 3.55?? Suggestions are lengthening the hose and/or installing a catch can so lube can get back into the diff. I've always run excellent rear lube, either RedLine MTL or Amsoil synthetic and still have the problem on extended highway drives and on the track. Design defect big time.
That's certainly NOT unique to the IRS at all. In fact most of the discussions surrounding catch cans and expansion lines for the diff are surrounding old-school stick axles.
 

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2k2GT
Where to start....
Be prepared for "factory tolerances" it might take some massaging to get the IRS up there.
Check the lower mounting bolts, ford in there wisdom has put 12mm bolts in some of the mounts, 14mm are what is needed, otherwise there will be a "clunk" in your IRS.
The 03 comes with the front cross brace, that is something I had to add afterward.
Replace the bushings with the MM bushings, that goes along way to stiffening things up.
Depending on your front spring rates you may need to adjust your shock/spring package to match, that is where I am at now. It seems like rear coil overs will help alot as well.
Both MM and Kenny Brown (boo, hiss) are stepping up with alot more parts for the IRS Sn8kbit has done more work on his IRS than I have and can talk about the KB stuff, you might want to track him down. Delk performance is only a couple of hours west of you, they have been working with him on the IRS.
Good luck! There is alot of potential in the IRS, it takes some work to make it right though.
 

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List of recommended things to do prior to install:

1. swap whatever gear you want to go with in.

2. Delrin or urethane control arm bushings. While you have it out, push up and down on the arms, see if they spring back or resist the movement. This resistance will vary from side to side, so will your wheel rate.

3. Install the urethane subframe bushings.

4. Install urethane or aluminum diff bushings. The aluminum works, it is noisy, almost too noisy for me. In addition, there is a gentleman on SVTperformance.com who has the rear diff bushings available in Delrin. Another must. Once that bushings starts to go, you'll feel it, and start trying to index the driveshaft to get rid of the vibration.

5. At the very least, rebuild the diff. I recommend, if you have the money, adding the Torsen T2, T2R, Black Gold DPI, or True-trac differentials. This mod alone made such a huge improvement in how the car "feels", I wish I had forked out for the T2R. A must in the IRS, a Must.

6. A quality diff cooler can be put together for just over 400 dollars, and with any gear over stock, it's needed. The one I put together is mounted under the rear bumper, no fans, and never got over 210* couple of weeks ago at Road Atlanta (90 + degrees outside). Simple to do, even more so with the complete IRS out of the car.

7. Address the rear bumpsteer. KB has their inner replacement pieces, and MM is about to release their IRS outer rod ends. Either one will fix this. Of course, bumpsteer adjustment will have to wait until the IRS is installed.

I won't recommend coilovers or springs. Talk to a professional ie: MM about what you need to go with. I'm pleased with my coilover setup with 650# springs. I may change the rear shock to a higher valved Koni 30 (30-7415 vs. 30-7647) and/or add 700# springs. I have a tad bit of oscillation in the rear when going over some sharp bumps, nothing unsettling, just there. You can add urethane sway bar bushings (I think 25mm, have to search the CC.com page for that...) and go with a bearinged endlink from KB.

{edit} You'll also need IRS exhaust. Delk has a couple (or did) factory 03 catbacks, I have the Borla I was running, I think Jed's (TennGT) contemplating hocking his FR500 exhaust, or you could fab up something simple and exit it out the side. That's what I've recently done with a set of single chamber Flowmasters.

yes, Jed, I will get pics this weekend....
 

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Discussion Starter #11
Thanks a TON guys. All those ideas sound like what I had in mind, but I really havent had to time to get on alota forums and ask around what is hype, and what is right.

I agree on the T2R, but budget restraints are gonna eliminate that im sure. Imma try and do all the bushings and what not, maybe not the alum., but deff. the urethane.

Basically, I was hoping to NOT hear that the upper/lower controll arms were crap and that i'd need the KB upper's and lower's to make the car feel right(which im sure it would help alot with them, but they are alota money).

I, personally will not be attempting this transplant......there is a shop lined up for that, that has the all important LIFT. No way im smart/patient enough to handle that mess.

Ill try and keep this thread posted on the updates and what not of how things are going.

Thanks
 

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The T2R is expensive, you can pick up the T2 from Reider for 425 shipped. It's what I opted for, and I'm pleased.

No one said the arms were crap. The bushings are. Those are what make the arms kick back. I've talked with the KB guys alot lately about their IRS setup, and I'm holding reservations. What we discussed about brake options for the rear make sense, but a friend of mine keeps breaking the upper arms, so I'm not completely sold. I have not, however, automatically decided that KB does not know what they're talking about. Good bunch of guys, and have been a good sounding board for improvements I've made, without purchasing any of their parts, other than IRS diff bushings.
 

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I was under the impression that the 03 and 04 Cobras had a differential other than the old traction lock.
 
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