[Mr.Soup]

thanks guys!!! any other suggestions?

Go to Full Tilt Boogie Racing Homepage and check out their rear bushing set for the IRS. that along with the irs brace and a set of 03-04 half-shafts and you'll be set. the bushing set is'nt cheap and if I'm not mistaken you'll have to upgrade the spiders in your pumpkin to 31 splines since your 99 has 28. however if you do the bushing kit alone you'll be out handling vettes and vipers. I would highly recommend the gear swap but in my opinion if your going 4:10s might as well go 4:30s. it's only a few hundred difference in RPMs. A lot of the people I know went with 4:10s and wish they'd gone 4:30s afterwards, our cars are heavy and the cubic inches are small so the more gear you throw at the car the better they respond. these

I have a full 04 IRS sitting in my garage and am getting ready to order the bushing kit myself, that with a set of 4:30s i already have and the Eibach sportline springs in my car now will make for a completely different car. the bushing kit is really involved and will take a couple days to do even if you're familiar with the set up thats why I sourced a seperate IRS and am doing it over the winter, that way come spring its drop the old one and install the upgraded one (sell old one to re-coop cost) im also upgrading shocks at the same time but am still up in the air as to which ones to get.

hope this helps, but again this is just one mans opinion.

 

[Mr.Soup]

Read This
The Mystery of the Cobra Independent Rear Suspension - SVTPerformance

i was gonna post that link i just figured the full tilt boogie racing one would stter him in the right direction too. that Bruce guy makes some seriously good bushings not to mention hes about as knowledgable as they come when it comes to mustang suspension

 

[Mr.Soup]

With just bushings your car will NOT out handle vettes and vipers. It will reduce hop and handle a little better. If you go to 03-04 half shafts you will have to get a new carrier because yours is a 28 spline. Spider gears have nothing to do with it so I dont know what Mr Soup was talking about. I have 4.10s in my '01 and love them. My freeway RPM went from 2150 at 80mph to about 2650 at 80 mph. The gears really wake the car up. I feel the 4.10s are great, but I might have gone with 4.30s had the others not been free.

Get the IRS diff cover brace for sure, and at least replace the subframe bushings with polys.

i thought the spider gears inside the carrier are what the axles insert into? if thats the case in order to upgrade to 31 from 28 all youd need is the spider gears right? the vipers and vettes comment was taken from the svtperformance website. in it Bruce (who makes the bushings) talks about how sloppy the factory bushings are while road racing, after making and installing his bushing kit he said he was out handling vipers and vettes. all the guys over on the svt performance board swear by the delrin\aluminum combination in the fulltiltboogieracing set compared to the MM ones. several guys on that site have talked about the MM ones deteriorating after just a couple years.

 

[Mr.Soup]

The FTB kit is HUGE on SVTP. MM is very much a serious player in road racing as well. I don't know anyone personally who has had the MM ones wear out, but it is poly so who knows. I would never bash FTB, nor am I am MM nutswinger. If I bought something that I regret I would say so. I do not regret the MM purchase as of yet. Although, like I said, I will probably be going over to the FTB delrin kit once I can down the car for a while.

the only negative i have heard about the FTB kit is the aluminum diff bushings transfer a lot of road noise into the cabin. i have been told its pretty signifigant but considering i have the LM1 catback and soon an off road X i doubt ill be able to hear much over that

 

[Mr.Soup]

i did some research on the cost of having bushings installed and its about 800 dollars so i was wondering if its a bad idea to put the 4.10 gears in w/o a bushing kit and maybe just with an irs brace. atleast for a little while. i dont really launch the car so im not sure what i can do. i really want to get some AFS wheels for it but i dont think ill be able too with the bushing kit. whats your input on it guys?

thanks!

yes you can just do the 4:10 swap, however the torque multiplication will amplify the wheel hop (in theory)

 

[Mr.Soup]

i guess what im trying to ask is do i really need bushings to put my 4.10 in and if i dont would i have to worry more about breaking IRS?

If you read the article on Full Tilt Boogie Racing Homepage they attribute most if not all the breakage to wheel hop. if you're careful to not stay in the throttle while it's hopping you shouldn't have to much to worry about.