View Full Version : IRS questions

01-18-2003, 12:08 AM
I'm in the process of building a Factory Five Cobra kit car and the kit includes using a T-bird Super Coupe IRS as the rear end assembly. The assembly manual said to use an ISR assembly from a 1989 to 1997 T-bird Super Coupe or from a Mercury XR7 1989 to 1992. The IRS should have a tag on the differential marker "3L2788". Which stands for 3.27ratio, traction locker,8.8 gear size. My question is, I have located a possible rear end, but the junk yard said it is from a 1997 SC with the "larger" rear brakes from the factory, with 16 or 17" wheels, and the worry is that my 15" Cobra Halibrand wheels won't clear the disc rotors. Can you help me with some facts on rear rotor sizes vs SC year or other options. I have also been told that there were no 1997 SC's and that they didn't offer a "larger" disc brake set. Or any other information that will help a non-Super Coupe expert make sure I get the "high torque" IRS with the 1.2 inch diameter half shafts. Buying these things over the phone from a junk yard dealer is a real trying experence. Any information will be a big help. Thanks

James Kanteraki
01-18-2003, 02:03 AM

I spend quite some time here and do a lot of work on SCs, but i don't have all the facts. I will confirm what i can for you and try to point you in the right direction. hopefully someone else will also reply.

'97 SC doesn't exist. Non SC with larger brakes, doubt it.
Now i "believe" that all tbirds had IRS. so technically you could get the housing from any bird/ cougar, but i think you would only be able to get the 3.27s and locker from an SC.
One thing you might want to try and find out is if the irs from a 99+ cobra is the same as the SC. I know it is also an 8.8, but i don't know if it can mount the same way the SC one does.
www.buyfordmotorsport.com and
they have all kinds of motorsport stuff for (what i thought was) good pricing. as for axles i guess you would have to know if there is a difference in the lengths between SCs and cobras, i know they have the same number of splines on the wheel side.
You can get axles from
www.raxles.com (i think thats the right link/spelling)

I'm sure doing business over the phone with a junkyard guy is rediculous, and probably long distance. parts plus shipping might just make it worth while to get your stuff from the links i gave you.

Also you should contact factory 5 after you gather some really solid info and make them change their directions. I hate it when companies selling a product don't have the knowledge to back up their sale.
Now?? are you going to use the tbird brakes with the kit kar??? Because i can tell you this for sure, there is no SC with 15 wheels. but i don't know if they would fit. I would hope that ford would not have had smaller brakes on the NA birds but ???

I hope this helped,

Thomas A
01-18-2003, 02:07 AM
Yes, there is no '97 SC. However they did offer a Sport option in '97, which among other things gave you slightly larger rotors. However, I am under the asumption that this was just done on the front rotors. I may be wrong though?

Yes, all '89-'97 Thunderbirds & Cougars came with IRS. And yes, you could get a 3.27TL 8.8" rear in one other then an SC. It was an option.

Yes, 15" wheel will fit with stock SC brakes. The actual size of the brakes didn't vary much from NA to SC models. The fact that you could get ABS and 4 wheel disc is what varied.