99 GT 'vert <-> 03 Cobra 'vert rear end swap

[merp]

I'm in the rather interesting position of having a two-Mustang household. I've got an 03 'vert, and the GF has a 99 GT 'vert. I'm tired of the wheelhop and various other driveline issues WRT the IRS, and my SO, while satisfied with her car, wouldn't mind if the rear end were a tad less "lively." I've got the opportunity to swap both rear ends, and the procedure looks relatively painless, but I've got a few burning questions that I can't seem to resolve with searches.

1. AFAIK, the stock 03 driveshaft is about an inch short for a 99-up live axle, but it should still work. Is this correct, and even if it is, would an aftermarket or FRPP DS be worth the money? Additionally, will the 99 GT driveshaft work with the IRS?

2. Given that the rear ends in both cars are roughly identical weight-wise, will the stock 99 springs/shocks be sufficient, at least in the short term? And secondly, will the stiffer springs/shocks in the IRS work okay in the GT? I'd like to be able to reuse as much stock componentry as possible, preferably on her car, as I want it to drive as close to stock as possible.

3. Are the stock catbacks completely compatible? From what reading I've done, it seems that some manual adjustment of the exhaust tips may be in order to make everything fit w/ the rear fascia in both cars.

Any info would be appreciated!

 

[FireRed04Vert]

(1) Why don't you just swap driveshafts too? As a matter of fact, some work there will be necessary because the flange size is different between the two. Anyway, it is from an 01 Cobra to an 03/04 Cobra. It seems to me that the most you might have to do swapping driveshafts is switch the slip yokes...and maybe a conversion joint.

(2) I can't imagine a problem with ride heights with springs. However, you may want to contact an aftermarket spring manufacturer and order up a softer set of springs for your GF car. The rates between the two may not be conducive to her type of ride.

(3) Can't help you there. Just measure the distances and heights between the two and see if they fit. They must because there are a ton of people who do this and I've never heard of it being an issue.

Also...check your gearing. You should have 3.55's. What does she have? That could be the whole bugaboo in the swap. If they're different, you're going to have to swap ring and pinions (they'll interchange) or get both cars tuned to the different gear ratios.

 

[merp]

1) I'm pretty sure that the output for the T-56 is different from the T-45. I'll probably just bite the bullet and buy two new driveshafts, as a direct swap isn't going to work.

2) I'll bet you're right. The GT 'vert has softer springs up front, and putting in a stiffer rear will make the car even more tail happy (see E0 1998 SVT Contours... yikes!) Altho, I've never heard of anyone making softer than stock springs, I could probably just beef up the fronts w/ dampers to match.

3) Again, if this looks to be too much of a pain, I"ll probably just get two new driveshafts. I know I can use the Ford 99 Cobra part in the GT, but I get the feeling that the 03 will end up being a hack.

I"m not too worried about the gearing, as the 3.27s in her car will work fine in a torquey car like the 03, and the weight reduction will offset the taller gears. The same should hold true for her car, only in reverse, with the shorter gearing offsetting the added weight of the IRS. I"ll have to get a Speedcal, tho, 'cause she'll want the speedo to work right