IRS Breaks

[may93]

Wednesday night at Norwalk, Ohio resulted in the breakage of the IRS Differential cover and driveshaft yoke. Compliments of the Mickey Thompson drag radials. Looking to replace the Differential cover with a heavier aftermarket one and install a bracket to support it. Haven’t seen anything else that is damaged!

I've removed and installed gears, axles, and most suspension parts involving a straight axle setup but the IRS is new to me as far as upgrades go.

I’ve looked on line and most post start with removing entire IRS assembly. I could be incorrect as I haven’t attempted it yet but I think I can remove the center differential without taking out the entire IRS. "Axle shafts and front and rear bolts." Not intending to change gears but I would like to put it on a bench and clean all the possible scrap aluminum out.

Anyone one here with the IRS that has made upgrades involving strength and traction issues? Car is a 2001 Bullitt with a Kenne Belle Supercharger making approximately 435 hp! Car only has 25,000 original miles so other than what broke the remaining suspension is in excellent shape.

[rtvickers]

Check out Full Tilt Boogie Racing. They make an IRS kit thats suposed to be the best. They are also making diff housing now. And if you have the money you can upgrade the half shafts to the DSS level 5's. There is a big debate over the L5's. They can still break. I would look into a brace also. Its been a while but I did some reading a few years ago about pulling the diff. I dont know if you can pull it without dropping the IRS. Which isnt hard. Hope this helps. You can go to svtperformance.com and do some research about the IRS kits and the L5's

[MWoods26]

I split one just like that in pretty much stock 99 Cobra I had many years ago. I wasnt even driving it that hard at the time. I thought it was a ujoint or something clunking around when I first heard something and thought I could make it the rest the way home... I didnt. I ended up just SRA that car. It is super easy to remove the whole IRS and would make it much easier to work on. As far as a diff cover goes I belive the Fore Precision works cover is the best one ever made but they quit making them. If you could find one used I think it is the way to go.

[Brandon Alsept]

Just remove driveshaft, pop axles out and then remove the front two mounting bolts and the center drops out. Normally you would have to remove 4 but you broke those loose already LOL.

They are kinda tricky to get shims in if you have to go to the aftermarket style thin shims.

[IWRBB]

All you need is a diff brace/aftermarket cover and the FTBR bushings. You could go with the upgraded toe links as well- just don't slide it into a curb with those beefy toe links.

What year IRS is it? If it's not from an 03-04 Cobra- you have 28 spline axles and diff, upgrading to 31 spline would be nice- but it's not totally necessary.

Do NOT buy the DSS axles. They have poor quality control and about half the people who buy those are still cussing DSS. Stick with the Ford half shafts. If they break, stick another one in there.

You could upgrade to an iron diff case from the older T-birds. Again, with the power you have I don't think it's needed- but if you are tearing it apart, you could.

What the IRS really needs more than anyhting else is a diff cooler. There's a bunch of info in the Cobra R forum on SVTPerfomance about making your own cooler system.

There's also the "Mathis brackets" mod... basically bolting/welding the upper/outer mount of the IRS to the sheet metal of the trunk- that's a fairly radical mod though, most guys don't go that far.

[slow86fiveoh]

U could sell the IRS and go for a solid axle swap and be worry free and those bushing kits aren't cheap

[700hp04mystic]

it broke from not having a diff brace end of story. they are like 179 bucks and that will fix alot of problems cheap.

[Jake]

http://www.billetflow.com/irs_brace.htm

I have this one. although stronger covers seem to be pretty popular too. fits great, and I drive pretty aggressively, and have raced it a couple times. no slicks yet though.

if you get aftermarket bushings, get a full kit. I have most of the bushings and still struggle with wheel hop. I'm sure my spring/shock set up and tires have something to do with it too though.

[may93]

I split one just like that in pretty much stock 99 Cobra I had many years ago. I wasnt even driving it that hard at the time. I thought it was a ujoint or something clunking around when I first heard something and thought I could make it the rest the way home... I didnt. I ended up just SRA that car. It is super easy to remove the whole IRS and would make it much easier to work on. As far as a diff cover goes I belive the Fore Precision works cover is the best one ever made but they quit making them. If you could find one used I think it is the way to go.
The car handles like its on rails with the IRS and makes the Bullitt handle like it should have from the factory. Considered changing it back to SRA but current setup makes for a great all around car!


Just remove driveshaft, pop axles out and then remove the front two mounting bolts and the center drops out. Normally you would have to remove 4 but you broke those loose already LOL.
They are kinda tricky to get shims in if you have to go to the aftermarket style thin shims.
Thats kind of what I had figured when I looked at it. Didn't see a reason to drop entire IRS for the center section.



All you need is a diff brace/aftermarket cover and the FTBR bushings. You could go with the upgraded toe links as well- just don't slide it into a curb with those beefy toe links.
What year IRS is it? If it's not from an 03-04 Cobra- you have 28 spline axles and diff, upgrading to 31 spline would be nice- but it's not totally necessary.
Do NOT buy the DSS axles. They have poor quality control and about half the people who buy those are still cussing DSS. Stick with the Ford half shafts. If they break, stick another one in there.

You could upgrade to an iron diff case from the older T-birds. Again, with the power you have I don't think it's needed- but if you are tearing it apart, you could.

What the IRS really needs more than anyhting else is a diff cooler. There's a bunch of info in the Cobra R forum on SVTPerfomance about making your own cooler system.

There's also the "Mathis brackets" mod... basically bolting/welding the upper/outer mount of the IRS to the sheet metal of the trunk- that's a fairly radical mod though, most guys don't go that far.
Decided to go with the heavy duty cover and bracket you've mentioned. It's out of a 2004 so its got the 31 spline axles and center section. Haven't seen the older T-Bird style you mentioned. Might be a good option though.



U could sell the IRS and go for a solid axle swap and be worry free and those bushing kits aren't cheap
I think with some basic upgrades the car will be ok with the IRS. Car has went 12.26s on street radials tires prior to the Drag Radials and yet handles curves well also.


it broke from not having a diff brace end of story. they are like 179 bucks and that will fix alot of problems cheap.
I agree 100%...

http://www.billetflow.com/irs_brace.htm

I have this one. although stronger covers seem to be pretty popular too. fits great, and I drive pretty aggressively, and have raced it a couple times. no slicks yet though.

if you get aftermarket bushings, get a full kit. I have most of the bushings and still struggle with wheel hop. I'm sure my spring/shock set up and tires have something to do with it too though.
Found the brace through Summit but having hard time locating the cover. Going to need a new drive shaft so figured good time for aluminum upgrade.


Check out Full Tilt Boogie Racing. They make an IRS kit thats suposed to be the best. They are also making diff housing now. And if you have the money you can upgrade the half shafts to the DSS level 5's. There is a big debate over the L5's. They can still break. I would look into a brace also. Its been a while but I did some reading a few years ago about pulling the diff. I dont know if you can pull it without dropping the IRS. Which isnt hard. Hope this helps. You can go to svtperformance.com and do some research about the IRS kits and the L5's
I've been looking at the Full Tilt Boogie Racing site. Definitely some good parts but possibly a little over kill for the amount of time goes to track. Concerned the aluminum bushings might be noisy on the road.

[IWRBB]

I beleive the brace only works with the stock cover. If you go with the FRPP or LPW cover, you shouldn't need a brace.

I'm with ya man- the IRS is great. Rides nice, handles great, and it's pretty damn tough. I love the "switch to a SRA and you'll be good" comment above. Yea, no SRA has EVER broken in a Mustang before.

[slow86fiveoh]

Ur right about the SRA breaking too but u don't have to worry about all those expensive bushings wearing out and those half shafts breaking don't forget the wheel hop u get if u don't use good bushings, my brother has a 99 cobra and my buddy has a 01 cobra so I've seen it all

[may93]

I beleive the brace only works with the stock cover. If you go with the FRPP or LPW cover, you shouldn't need a brace.

I'm with ya man- the IRS is great. Rides nice, handles great, and it's pretty damn tough. I love the "switch to a SRA and you'll be good" comment above. Yea, no SRA has EVER broken in a Mustang before.

I decided to go with the FRPP. The bracket utilizes the stock parts and from what I've read and seen the bracket just reinforces an already weak and under engineered factory cover.

I've worked on SRA's before and even they will hop without the proper traction bars, upper and lower control arms, and correct pinion angle. With the IRS I'm not new to the mechanical aspects of 8.8's but more so what aftermarket parts work on it!

The IRS definitely improves the handling of the car though. If I was turning it into a drag car I'd sell it and go with a SRA but for the street the IRS is perfect.

[IWRBB]

Ur right about the SRA breaking too but u don't have to worry about all those expensive bushings wearing out and those half shafts breaking don't forget the wheel hop u get if u don't use good bushings, my brother has a 99 cobra and my buddy has a 01 cobra so I've seen it all

99 and 01 IRS are not the same as 03-04 IRS. The 99 has the 28 spine halfshafts and diff. No pinion support either. The 01 is better, but the 03 still has improvements- better halfshafts, and stiffer bushings.

Let's just say I've made at least 50 passes down the drag strip, with about 550 HP, on drag radials (not kind to the shafts compared to wrinkle wall slicks) without issue. My car does have the diff brace- and that's it. I give it hell on the street- I've hopped the rear end dozens of times (not an issue with sticky drag radials though).

I can afford to replace bushings- it's really not that expensive. The more expensive ones are the MM/FTBR solid alumnium and delrin bushings- which really aren't going to wear out. The only common wear points that the IRS has that the SRA doesn't are the cross axis joints for the spindle, and the wheel bearings. THOSE are both expensive, but it's just how it is if you want a big HP car, along with a nice supension setup. Vettes and Vipers eat the exact same parts.

Obvisouly if all you do is drag race, a SRA is a better choice. For a street car- I think you are dumb to swap out a IRS for a SRA. There are plenty of guys with 03/04 Cobras running over 700 HP through the stock IRS (with the cover brace added), pulling the front wheels and running 9s. All it takes is slicks, the right struts/shocks, enough power and some balls.

The one thing I don't like about the stock IRS is the bushings will allow it to squirm under full throttle and get get a bit of rear steer sometimes. Yes, I plan to put those expensive bushings in there. I'll be happy as a pig in shit at that point :)

[may93]

99 and 01 IRS are not the same as 03-04 IRS. The 99 has the 28 spine halfshafts and diff. No pinion support either. The 01 is better, but the 03 still has improvements- better halfshafts, and stiffer bushings.

Let's just say I've made at least 50 passes down the drag strip, with about 550 HP, on drag radials (not kind to the shafts compared to wrinkle wall slicks) without issue. My car does have the diff brace- and that's it. I give it hell on the street- I've hopped the rear end dozens of times (not an issue with sticky drag radials though).

I can afford to replace bushings- it's really not that expensive. The more expensive ones are the MM/FTBR solid alumnium and delrin bushings- which really aren't going to wear out. The only common wear points that the IRS has that the SRA doesn't are the cross axis joints for the spindle, and the wheel bearings. THOSE are both expensive, but it's just how it is if you want a big HP car, along with a nice supension setup. Vettes and Vipers eat the exact same parts.

Obvisouly if all you do is drag race, a SRA is a better choice. For a street car- I think you are dumb to swap out a IRS for a SRA. There are plenty of guys with 03/04 Cobras running over 700 HP through the stock IRS (with the cover brace added), pulling the front wheels and running 9s. All it takes is slicks, the right struts/shocks, enough power and some balls.

The one thing I don't like about the stock IRS is the bushings will allow it to squirm under full throttle and get get a bit of rear steer sometimes. Yes, I plan to put those expensive bushings in there. I'll be happy as a pig in shit at that point :)

Oddly enough got car back together and broke axle first time out. The Mickey Thompsons do work. Its a 04 already utilizing the 31 spline axles so it does have the better choice compared to the 28 spline. You mentioned having different axle shafts. Just curious what axles your running if not stock?

[04 Venom]

I beleive the brace only works with the stock cover. If you go with the FRPP or LPW cover, you shouldn't need a brace.

I'm with ya man- the IRS is great. Rides nice, handles great, and it's pretty damn tough. I love the "switch to a SRA and you'll be good" comment above. Yea, no SRA has EVER broken in a Mustang before.

I agree; keep the IRS.

[SN95N/A]

Not to hijack jus a quick ?..what power are these irs exactly good to,I got 03 cobra(734hp) it has a diff cover brace but everyone tells me "im surprise ur irs is still in tact" am I passed the power level that that irs can with stand with just a brace?

[rtvickers]

Not to hijack jus a quick ?..what power are these irs exactly good to,I got 03 cobra(734hp) it has a diff cover brace but everyone tells me "im surprise ur irs is still in tact" am I passed the power level that that irs can with stand with just a brace?

They're probably surprised it hasn't broken or you haven't went SRA yet. You should be good at that power level. I've heard of some high horsepower cobras on IRS

[MWoods26]

Not to hijack jus a quick ?..what power are these irs exactly good to,I got 03 cobra(734hp) it has a diff cover brace but everyone tells me "im surprise ur irs is still in tact" am I passed the power level that that irs can with stand with just a brace?

The IRS is "exactly good to" 845.68 rwhp.....:D There is no magic number man if its going to break its going to break. I broke one in a basicly stock car and I know of more than a few that are still holding up in some real high power cars. There are alot of variables to it. Your car makes over 700 hp but if you drive it easy and never see the track it will likley last forever where a guy with much less power that launches off the rev limiter 10 passes every weekend will be looking for parts to put it back together pretty soon. I was researching the same sort of question as far as the stock bottom end in my 04 Cobra being OK in the 700+ range and its the same damn thing. Guys have blew them apart at numbers far less than other guys have been pushing for years. Luck of the draw I guess.

[smytty]

The IRS is "exactly good to" 845.68 rwhp.....:D There is no magic number man if its going to break its going to break. I broke one in a basicly stock car and I know of more than a few that are still holding up in some real high power cars. There are alot of variables to it. Your car makes over 700 hp but if you drive it easy and never see the track it will likley last forever where a guy with much less power that launches off the rev limiter 10 passes every weekend will be looking for parts to put it back together pretty soon. I was researching the same sort of question as far as the stock bottom end in my 04 Cobra being OK in the 700+ range and its the same damn thing. Guys have blew them apart at numbers far less than other guys have been pushing for years. Luck of the draw I guess.
I had a 04 making alot of power back in the day....
Buy a few half shafts just as a back up... DR are far worse on the HS then anything.. If you wanna track the car get full blown slicks, the wrinkle when taking off absorbs some of the shock....
As for power on a stock block , its all about the tune....

[SN95N/A]

I just usually do highway pulls with my car,or it sits in the garage.but thank you for the info.

[Dirtyd0g]

Check out the LPW cover it helps a ton, the girdle support is important for these IRS cars they wheelhop different from solid axle cars. Sadly I have seen that a few times on MN-12 cars.
Alan