Advice from people who have done the IRS swap?

[ClayBelt]

Going to be picking up a 2001 Cobra IRS to put in my 1986 SVO later this month. Any advice from anyone who’s done the swap?

[wraithracing]

You have to run the IRS specific exhaust tailpipes. You have to run HIGH offset wheels that are generally S197 Mustang offset if using "common" or "popular" mustang wheels in the back. The 2001 is the weakest of the Cobra IRS (yes I have one too) shouldn't be a big issue for an SVO, but can become a problem behind a healthy V8 or really hopped up Turbo 4/6. Most likely you will need to replace the spindle cross axis joints https://www.maximummotorsports.com/C...IRS-P1228.aspx I personally haven't seen a set yet that wasn't bad, but hopefully yours is different. Most likely you will need/want to replace all the suspension bushings since that is one of the weak spots of the the IRS and generally improves the overall handling and ride characteristics of the vehicle when replaced. I think the 2001 has the better heavy duty crossmember, but if not, then you want to consider that too. You will want the better subframe mount bushings again since that locates the whole rear suspension. The differential mount bushings are another area of concern that generally needs to be addressed, especially due to age and wear if the suspension has any decent mileage on it.

So bottom line its a cool upgrade to the average Mustang with a TON of headaches. I have done two and have another sitting under a bench that I haven't decided about yet. My 79PC has my first and I did another for a buddies' 86 GT years ago. I know of another was installed in a 1986 SVO along with a full compliment of Maximum Motorsports and Full Tilt Boogie parts to get everything out of it. When done right and tuned properly it is a nice handling and riding setup. Otherwise . . . Not sure its worth all the headaches and added costs over a quality 8.8. That is my dilemma with installing it in another Fox.

The wheel offset can really be a big issue depending on your wheel choice as you need to run at least a 36mm offset on a 9" wheel and honestly I would prefer 40mm for added clearance from the wheel lip even rolled. I have 255/40/17 on the rear of the PC and they have still been nicked a time or two due to lack of clearance.

Don't forget to get the chassis brackets that attach to the quad mount locations on the outside of the frame rails. Those also limit your wheel sizing which can be annoying, but the only other option is going to be the hard mount modification. I have considered doing the same, but just not a priority yet. When the PC gets its refurbish it might be. Feel free to ask other questions as I am sure I have forgotten or skipped things in this rambling post. Good Luck!

[ClayBelt]

I was told it “needs bushings” so I suspect those cross axis are shot. I’ve got 17x7.5 ET43 steelies off a 2008 Crown Vic on the car currently, probably will continue running them barring another issue. Supposed to pick up the IRS in the next week or two. Do you think the Prothane poly kit would be bad for the rest of the bushings if they are bad?

[wraithracing]

I like Prothane products and have used them on several projects over the years. I personally have only used Maximum Motorsports and Full Tilt Boogie Racing parts/bushings in my IRS units. I believe Prothane may be the manufacturer for Maximum Motorsports, so they may be the same bushings, but I can't confirm. Personally I would just order from either of the two vendors listed depending on your preference. Both offer much of the same products for the IRS, but there are some differences in product lines and design philosophy. I will say that the number of bushings and the work involved to swap them all out of the IRS is much different than a solid axle and the quadra bind rear suspension. Good Luck!

[ClayBelt]

Thanks man!

[86lx]

The swap itself is really straight forward. We haven’t been able to drive the car enough to really sort anything else out.

Currently running 99 GT 17x 9 wheels. They rub a little on bumps, but the car is also sitting pretty low. Whenever we get around to buying new wheels we will make sure to get the proper offset.


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[Patrick Olsen]

The swap itself is really straight forward. We haven’t been able to drive the car enough to really sort anything else out.

Currently running 99 GT 17x 9 wheels. They rub a little on bumps, but the car is also sitting pretty low. Whenever we get around to buying new wheels we will make sure to get the proper offset.

If they're OEM wheels, then they're 17x8".

[86lx]

If they're OEM wheels, then they're 17x8".

Could be


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[ashley roachclip]

01 is actually a 31 spline axle , same as 03-04 .
99 was the week one at 28 spline .
I have done several of these swaps .
Anything that has rubber should be replaced as it is old .
Not a big deal .
I welded the rear brackets to the car , saved cutting the frame rails and adding more parts to bolt the bracket as was done on the Cobra .
It is just bolts .
Not that hard and the results are worth the effort .
I would swap Cobra brakes to the front , to balance the package .

[ClayBelt]

I’ll have to keep in mind welding the brackets as an option. Just did cobras up front and was contemplating between a watts link/torque arm or IRS when this one popped up and made my decision for me.