When do I need to upgrade from 28 to 31 Spline axles?

[cobrasvtcoupe25]

I have a 1999 cobra with 28 spline axles stock and wanted to know when these stock axles are going to snap and how much they can take. I love going out to the track, but don't want to break anything.

I'm planing to go with 4.10's in the future and hope to put down around 300rwhp 300rwtq.

How much rwhp and rwtq do these things handle.

I know the 2001 cobra comes with 31 spline axles.

 

[04YELLOWGT]

I would worry about beefing up the IRS. That will break befrore your axles will.

 

[cobrasvtcoupe25]

I would worry about beefing up the IRS. That will break befrore your axles will.

That’s encouraging

 

[BennyBlown2v]

Uhm...he's talking about "beefing up the IRS"! Halfshafts (axles) are one of the FIRST things to brake on a Cobra IRS; the actual subframe is incredibly strong, so are the control arms and even the diff cover isn't that bad unless in a higher HP application (stock 03/04 cobras are known to break them) or when you have excessive wheelhop. The halfshafts in the 99 cobras aren't that great, I would swap them out for some 03/04 cobra parts (31 spline). Also you should look at 03/04 (cobra-r style) brace, and a billetflow IRS brace to keep the cover from breaking. DSS also makes halfshafts which can support 1000+hp

Hard launches and wheel hop are what kill these parts - so eliminating wheel hop is a great start! I would checkout www.maximummotorsports.com as they have the best IRS parts bar none; get subframe bushings, diff bushings (I use urethane, but aluminum is best), and control arm bushings. Also, IMO, the BEST mod for the IRS and reducing wheel hop is a set of coilovers as they allow a higher wheel rate with lower spring rate so you can run a softer spring with better results in handling.

 

[SVT32VDOHC]

300RWHP won't harm the splines. My 28's held up for ever with 1.8 6o ft times, Drag radials and 40-50 passes on the drag strip. What failed was the clutches in my diff. MY axles were still in great shape. I would get 31's if you plan on running slicks and pulling 1.5-1.6 60 footers and running 11's.

 

[cobrasvtcoupe25]

Uhm...he's talking about "beefing up the IRS"! Halfshafts (axles) are one of the FIRST things to brake on a Cobra IRS; the actual subframe is incredibly strong, so are the control arms and even the diff cover isn't that bad unless in a higher HP application (stock 03/04 cobras are known to break them) or when you have excessive wheelhop. The halfshafts in the 99 cobras aren't that great, I would swap them out for some 03/04 cobra parts (31 spline). Also you should look at 03/04 (cobra-r style) brace, and a billetflow IRS brace to keep the cover from breaking. DSS also makes halfshafts which can support 1000+hp

Hard launches and wheel hop are what kill these parts - so eliminating wheel hop is a great start! I would checkout www.maximummotorsports.com as they have the best IRS parts bar none; get subframe bushings, diff bushings (I use urethane, but aluminum is best), and control arm bushings. Also, IMO, the BEST mod for the IRS and reducing wheel hop is a set of coilovers as they allow a higher wheel rate with lower spring rate so you can run a softer spring with better results in handling.

If I upgraded to 31 splines would I have to get a 31 spline diff too?

 

[isjoining]

yes you would

 

[the98stang]

Don't fix it if it ain't broke!

No really, just give those axles hell, and when they break, they break. It's a gamble, they might hold the power, they might not. Just save your money.

 

[BennyBlown2v]

Don't fix it if it ain't broke!

No really, just give those axles hell, and when they break, they break. It's a gamble, they might hold the power, they might not. Just save your money.

Problem is when you break axles in an IRS often you break the carrier (meaning whole diff), and diff housing, and sometimes the knuckles too.

 

[the98stang]

Problem is when you break axles in an IRS often you break the carrier (meaning whole diff), and diff housing, and sometimes the knuckles too.

Ya, but it MIGHT not happen. I would rather spend the money elsewhere, but that's just me

 

[04YELLOWGT]

Also better make sure you have a way to get home to because when they break you aint driving it.

 

[the98stang]

It most likely won't break unless he's running slicks and dumping the clutch at 5k. On street tires, I doubt it, even with massive amounts of power....