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Old 10-09-2009, 02:44 PM   #1
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Default IRS to SRA....need help

So I broke my drive shaft and broke my diff cover, now I am faced with the dilema to either go SRA or (re)build the IRS...



Few things I need to know right off is the following

1. IF I switch to a SRA would one out of a 2000-2004 GT be better then one out of an 03/04 Mach?

2. I need a Posi unit, or "traction lok" as ford refers to it, both tires spinning simotaniously and receiving equal power, correct me if I am wrong but didn't the 2000-2004 GT's come with limited slip? which is NOT the same thing? My understanding is limited slip is a "one tire fire" that slips the other wheel in and out of power to get traction....similar to the posi, yet different.

3. Do I keep my same lowering springs and other suspension parts? what needs to be changed?

4. What other major components need to be changed? say I get my hands on a 03/04 Mach rear end, what needs to be done to actually make this work?

5. Is there an indepth guide, or any guide for that matter on doing this swap on here or any other forums?

6. Is it really better to swap to SRA or to just repair the IRS, slam, brace, and add some bushings?

7. What are the major pros and cons of this operation?
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Old 10-09-2009, 02:47 PM   #2
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Limited slip is a general term for a differential that transfers power from one tire to another. Posi is the term gm coined in the 60's for their version of the limited slip "Posi-traction". For some reason you think posi means locker which is a differential that will lock both tires up like a spool under power, sending equal power to both wheels.

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Old 10-09-2009, 03:08 PM   #3
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Thank you Eric, now lets wait for some other responses

Also you gonna come up here this winter and gimmie a hand with this swap?
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Old 10-09-2009, 03:09 PM   #4
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Originally Posted by Amplejester View Post
Thank you Eric, now lets wait for some other responses

Also you gonna come up here this winter and gimmie a hand with this swap?
no, but i'll gladly come up there and show you how to drive it when its done next summer
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Old 10-10-2009, 04:53 PM   #5
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you can use the rear end housing of a 99-04 car (including mach 1's) or you can use a 1998 or earlier housing, if you go with the latter your tires will sit inside the wheelwell about 3/4" deeper than the 99-04 housing.

you also need springs, shocks, exhaust, and GT brakes if you dont use a Mach 1 rear end.

its EASY to do, I did it in my garage with the help of a buddy.
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Old 10-10-2009, 05:12 PM   #6
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Is your car a drag race only car? If it's not then I suggest just fixing the IRS and putting a better diff cover rather than a stock cover with a brace. The IRS is better for a street driven car because it handles better and retains traction over uneven surfaces better. If we all lived in the southwest where the roads are like glass then I'd say swap it but otherwise stick with what you've got. The other thing to remember is that the stock SRA is not bulletproof right out of the box. As a matter of fact, it's quite flimsy. You need to get upgraded axle tubes, better gear, all kinds of triangulation arms and other crap just to make it decent. Oh, and don't forget that you need a different exhaust too. IMO you need bushings and a diff cover for the IRS. Buy a couple of extra axles just in case but the most important thing about not breaking the axles is to preload the drivetrain on launch and get out of it if you are getting wheelhop. With bushings you shouldn't get wheelhop though.
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Old 10-10-2009, 05:18 PM   #7
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Is your car a drag race only car? If it's not then I suggest just fixing the IRS and putting a better diff cover rather than a stock cover with a brace. The IRS is better for a street driven car because it handles better and retains traction over uneven surfaces better. If we all lived in the southwest where the roads are like glass then I'd say swap it but otherwise stick with what you've got. The other thing to remember is that the stock SRA is not bulletproof right out of the box. As a matter of fact, it's quite flimsy. You need to get upgraded axle tubes, better gear, all kinds of triangulation arms and other crap just to make it decent. Oh, and don't forget that you need a different exhaust too. IMO you need bushings and a diff cover for the IRS. Buy a couple of extra axles just in case but the most important thing about not breaking the axles is to preload the drivetrain on launch and get out of it if you are getting wheelhop. With bushings you shouldn't get wheelhop though.
every mustang made except for 99-04 cobras has had a solid axle in it, its really NOT THAT BAD!!

no triangulation bars needed!!!

to the OP if you are going solid make sure it is a bulit solid.

If you wanna keep the IRS just buy spare halfshafts and make sure you use a tire with some decent sidewall
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Old 10-10-2009, 07:42 PM   #8
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Quote:
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every mustang made except for 99-04 cobras has had a solid axle in it, its really not that bad!!

No triangulation bars needed!!!

To the op if you are going solid make sure it is a bulit solid.

If you wanna keep the irs just buy spare halfshafts and make sure you use a tire with some decent sidewall
irs ftw
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Old 10-11-2009, 12:40 AM   #9
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Contemplating keeping the IRS and just beefing it up (bushings, drop it with some lowering springs, stronger diff cover, etc)

How hard is it to swap out diff covers? just those 8 or 10 bolts? or is there a lot more to it?
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Old 10-11-2009, 10:28 AM   #10
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you have to remove the diff assembly to replace the diff cover.
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Old 10-11-2009, 03:18 PM   #11
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Somewhat of a thread hijack.

What makes the diff covers of those cars crack in the same spot like that? Every time I see them break it's the same thing.


To the OP...how often do you drag race? If the answer is a lot, as long as you're going to have to take it out you might as well put a solid back in.
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Old 10-11-2009, 06:32 PM   #12
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you will need:

a set of control arms (upper n lowers)
good differential
set of axles
pair of rotors if you go gt ..nothing if you go mach 1
abs lines

a stock setup will get you by but only for mormal driving purposes. i did it all at once and its a huge difference on these cars. yeah itll hop over bumps but if you watch any IRS car at the tack grab gears you can see the rear tires move an inch or better back and forth in the fender and that just scares me. the IRS was an afterthought in these cars and really shouldnt be there

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Old 10-17-2009, 09:11 AM   #13
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1. IF I switch to a SRA would one out of a 2000-2004 GT be better then one out of an 03/04 Mach?

No it won't be better but it will be easier to find.

2. I need a Posi unit, or "traction lok" as ford refers to it, both tires spinning simotaniously and receiving equal power, correct me if I am wrong but didn't the 2000-2004 GT's come with limited slip? which is NOT the same thing? My understanding is limited slip is a "one tire fire" that slips the other wheel in and out of power to get traction....similar to the posi, yet different.

Not exactly. Posi means to spin both tires at the same time. Limited Slip means that under turns it allows the diff to slip so that the tires spin at different speeds to reduce tire wear and prevent hopping. I don't know the technical term but I think the one tire fire you're referring to is an open diff, found in the V6 mustangs.

I'm 90% sure the stock mustang GT diff is posi and limited slip.

Since you already have the Eaton diff in the IRS, you could use it if it is not destroyed. I'm 100% sure that it is Posi and Limited Slip.

http://www.streetrodderweb.com/tech/...ited_slip.html

3. Do I keep my same lowering springs and other suspension parts? what needs to be changed?

The lowering springs and street tires is what caused the failure. That's a recipe for wheel hop and wheel hop equals what you just experienced.

I would use the stock GT springs in the rear and cut em down a coil. GT brakes and calipers aren't necessary but it is nice if you decide to put some fatties on back. I believe you can make the existing catback work but otherwise you need a GT catback system and the exhaust system hangers out of a GT.

4. What other major components need to be changed? say I get my hands on a 03/04 Mach rear end, what needs to be done to actually make this work?

Everything I have for sale here....

http://www.chicagosvt.com/forums/showthread.php?t=40683

I have the GT springs, exhaust hangers, caliper brackets that I could include in the package above.

5. Is there an indepth guide, or any guide for that matter on doing this swap on here or any other forums?

Get a Hayne's manual for a GT. I didn't end up doing the swap but my understanding is that it is fairly straight forward and easy to do. If you change your own brakes then I'd say go for it. I think the hardest part will be the brake lines and bleeding the system.

6. Is it really better to swap to SRA or to just repair the IRS, slam, brace, and add some bushings?

Better is a subjective thing. Your IRS probably failed because of wheel hop, if you wheel hop any rear end bad things can and probably will eventually happen. If you want to launch a car and minimize this you need a good suspension system...either IRS or SRA can be made to handle plenty of power. With a good suspension system there is a tradeoff....better suspension for launching...the worse the ride quality.

You need to make a decision, something bulletproof and sacrifice ride quality....or stock or lowered suspension and avoid launching the car hard.

7. What are the major pros and cons of this operation?

Pros - The first time you put some sticky tires on it and launch at the track with a properly set up suspension the feeling of being thrown back in the seat will convince you that you made the right decision.

Cons - The first time you drive it and turn on an entrance ramp and realize you need to slow down because you have way too much body roll you'll realize that you made the wrong decision.

I just sold my cobra so if you decide that you're interested in the stuff I'm selling I'll make you a good deal. I was contemplating hanging on to the stuff but I probably won't buy another mustang for another year or two. Hope that helps.
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Old 10-17-2009, 09:19 AM   #14
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Just to clarify, don't run the stock GT rear without upgrading the diff to a 31 spline and getting some axles. I don't have that included in what I'm selling...the stock stuff is 28 spline I believe.
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Old 10-17-2009, 12:16 PM   #15
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You also must have an exhaust (cat back) for a solid axle car. The SRA and IRS setups are totally different.

The swap isn't hard. I did mine by myself a long time ago. It can get pricey though. figure if you use all new parts, you'll end up around $4,000.

If you get a used setup, you will still end up building up the diff and probably the suspension too.

On the plus side, the IRS can be sold to recoup some of the cost.
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