Gen 3 Coupe build with IRS

[Fasteddie41458]

Hello, a question on my build regarding the IRS half shafts. Considering to use ford racing heavy duty half shafts for 2015 mustang gt. Anyone use these ford racing half shafts, do these fit our gen 3 coupes?

[David Williamson]

The Mustang half shafts don't fit, the Coupe ones are shorter. Some are running over 700 HP with no issue with the FFR parts.
David W

[Fasteddie41458]

Thank you for the information.

[edwardb]

To expand slightly on David W's answer -- agree the Factory Five supplied IRS parts are shorter than those on a Mustang. They do however contain the OE Ford constant velocity (CV) joints. The Ford part number is on the parts. I personally have not heard of a single failure of the provided axles for this application. Keep in mind how much lighter these cars are than a Mustang. Upgraded aftermarket parts aren't needed IMO.

[only1moreracecaripromiss]

Agreed with all here. I considered these as well since I will have a high HP/Torque set up. Most homework I did on the drive train, clutch, trans options was convinced that since the weight of the cars is so much less than "new" cars all these parts don't have the same load on them.

[Skuzzy]

Being the physics geek I am, I ran these numbers a while ago. Like others have said, you are not going to break any of the stock drivetrains bits in this car, regardless of the torque or tire size. The only potential weakness is the half-shafts/axles.

Are they new bits FF had made, or are they cut down from the stock axles?

If cut down, were the new splines cold rolled or cut? If cut, that would be the weak link. You can heat treat cut splines and it helps, but it still will not be as strong as cold rolled splines.

If they were made, are they forged or machined? If machined, cold rolled or cut?

EDIT: Forgot the to add. In case it was not known, Tremec rates their transmission using a 5,000 pound load.

[David Williamson]

I believe the half shafts are made for FFR but no idea what the splines are. But unless you are planning an all out drag car they will be fine, the tires will spin first. I don't know of anyone that has had a failure with the new style IRS.
David W

[Skuzzy]

If I sounded like I was implying they were not up to the task, allow me be clearer.


I did not mean to imply or infer the shafts were not up to the task, regardless of the method used in manufacturing. The OEM shafts were made for a car much heavier than the Coupe making it really difficult to make a replacement set which would not be up to the task.

Sometimes I will get caught up in the minutiae......Okay, okay,...a lot of the times.