doing IRS swap..upgrades and gears question

[Night Shifter]

i found a guy local on svtperformance that is wanting to swap his irs for my sra so i will be going through with the swap but i have a few questions on upgrades..

is there any kind of rear lower control arm upgrade for irs...i know lakewood makes one for the irs on the new camaro but not sure about for mustangs...also, can i still run a torque arm or will it not be needed with irs? i plan on replacing all irs bushings when i do the swap and i know that will help a little bit but im trying to get all i can out of the irs...eventually ill be going with this kit

IRS Rear Grip Package - Street, 1999-04 Cobra [MMRG-21] : Maximum Motorsports, the Latemodel Mustang Performance Suspension Leader!

but at that price ill be waiting a little while...

when it comes to rear gears on an irs, can i buy the same ring an pinion for a sra or is it a whole different set up? ill be going with 4.10's this time though....thanks for any info guys

 

[stprorolla49]

This is awesome, so many GT guys are swapping over to IRS now! I did mine over the summer, and it was one of the best mods I've made to the B thus far. As far as I know, there aren't any control arm upgrades for the IRS, but it isn't really necessary since its not one of the IRS's weak points.

As far as bushings, for the time being, I would just get the MM urethane subframe bushings and front/rear differential carrier bushings. These bushings can't be changed (obviously) when the IRS is in the car, but the control arm bushings and tie rod ends can be done when the IRS is in the car, so you could do them a little down the road when you have the money and you won't have to rip the IRS out of the car. I just got these bushings for Christmas this year from the gf and I can't wait to get them in.

As far as gears, yes its the same ring and pinion as an 8.8. I have 4.10's in my IRS and I LOVE them! Defintely wakes the lil' 2v up.

Just out of curiousity, what year IRS will you be getting? If it's not an 03-04, I might consider passing and continuing the search. The older (99/01) IRS's had some problems and aren't nearly as strong.

Good luck with the swap

 

[Night Shifter]

awesome info... its coming out of an 03 cobra.. i was planning on pming you about it anyway lol...thanks for the info about the carrier bushings i really cant wait to do this install...and for the bushings i just planned on doing a slight freshening up for now and going all out later down the road.

and now i can run 4.10's cause ill get them mega cheap through work! can i use the rebuild kit i used in my sra for the irs or are there different bearings/shims in the irs?

oh yeah, someone mentioned some kind of y block or something to hook the rear brake lines up? dont know if thats true or not but will i need anything to hook the brake lines up or will the just be the same?

 

[darkside03gt]

OK here we go. I did this swap myself a year ago.

First off kenny brown used to make a lower control arm for the irs. Just about everyone who ran them had one problem or another. The real downside to running KB's lower control arm is that it requires cutting and re-welding of the mounting tabs so it will cost you $$$. The lower control arms fix a camber problem the IRS has. Its not a huge problem but I have been told that once its corrected there is a benifit but only to die hard track cars and guys who really know how to push the car. One thing that would steer me away from buying a set of used KB arms is the fact that it seems that KB had more then a few QC issues.

As far as bushings go take a look at full tilt boogie racing. They make an entire bushing kit for the irs that includes mounts for the pumpkin and control arms. One thing I really like about the FTBR kit is that it comes with greese fittings. Ontop of that the kit is less expensive and there have been zero complaints about it and I researched for two months before I bought mine.

I drove a almost stock cobra with an IRS before I put my IRS in with the FTBR kit and I can tell you that it is a great kit and I would not install a IRS without one again, period.

Yes you can run standard 8.8 rear gears. However you may want to think twice about running 4.10s. 4.10s will make a lot of noise and some guys who have installed that DD their cars have removed them because they are so bad. I can actually hear my stock 3.55s with the FTBR bushings. I would install some dynamatt over the pumpkin on the inside of the car if you go with 4.10s.

Before you install the IRS order MM's low profile rear mount bolts so you dont have to worry about tire clearance issues. This is a problem because the rear mounts for the IRS replaced the rear mounts for your quad shocks and they mount to the outside of the frame rail. Some guys grind down the bolt head a little but I think that its not a good idea. This is only a problem if you have rear rims that are larger then 17x9. I would buy the front subframe bolts from FTBR when/if you order the kit. Basically ford installed bolts in the front mounts that were to small and cause issues.

No you cannot run a torque arm with the irs. Its not even possible nor is it needed. When you see the IRS up close you will understand.

Also make sure you remove your pinion snubber before you install the IRS. I made that mistake and couldnt get the holes on the mounts to line up with the torque boxes and rear mounts. Make sure you change your fuel filter too because once the IRS is installed its next to imposible to change it without at least lowering the rear of the IRS. I would also consider changing the clutch pack in the T-lock when you do the gears. Mine was completely shot. Go ahead and install MM's braided rear brake lines while your at it. Yes they will fit.

As far as the braking I am not sure but I have been told that there is a line you can buy from ford to remedy the problem you will have. I believe it all comes down to the routing of the hard line to the passenger side.

Feel free to PM me if you run into problems or have any questions and I'll do my best to help you out.

 

[LaserSVT]

Really the only changes for earlier IRS is no pinion brace and then 28 spline axles. Other then that they are the same.

Ive built up quite a few of these things though and they really do kick the SRA INHO.

Now what I have learned that are really needed and whats kinda a waste.

If you wanna make under 600 rwhp then dont bother with subframe bushings cause the car will clunk like crazy and the stock ones are plenty firm for any power levels under that.
Diff cover brace IS A MUST! Too many times ive seen cracked covers because the aluminum is too weak. Billetflow makes an excellent one and so does Steeda but the Billetflw one is nicer.
As mentioned, poly diff to subframe bushings is a very good idea.

The biggest thing you will want to do to help eliminate wheel hop is Delrin lower controll arm bushings. These are a major PITA to screw with but if the IRS is out already it makes them much easier. They are well worth the $350 and eliminate 80% of the wheel hop associated with Fords IRS. Just make sure you properly shim them with no binding and dont forget to use ALL the grease they come with.

This is a 99 unit I just upgraded with all that stuff and you can see the white Delrin bushings.
View attachment 198936

 

[LaserSVT]

Wow, a lot of good info from others here.

Just a couple years ago nobody knew anything nor wanted to do it. I am glad to see that not only are people doing it now but they also did the right and proper homework.

Good job Stangnet!

 

[Night Shifter]

damn thanks for the awesome info guys!!

did either of you have any issues with the stock main brake lines? or did you guys just bolt and go?

thanks guys!

Dark i may en up PMing you in the next week or so

 

[darkside03gt]

I had zero issues with brakes. Mine is a 03gt though. I believe the line you need comes from a 99/01 cobra but i am not sure. I would jack up the rear end of your car and trace your hard lines and find out.

 

[SublimeRT]

Full Tilt Boogie Racing

Enjoy.

 

[darkside03gt]

damn thanks for the awesome info guys!!

did either of you have any issues with the stock main brake lines? or did you guys just bolt and go?

thanks guys!

Dark i may en up PMing you in the next week or so

Hey no problem I am online just about everyday.