I know the rear ends on the 04 Mustang GT are 28 spline stock. If I want to upgrade it too a 31 spline all I need is the rear diff and axles correct? Do I need to upgrade the driveshaft?

 

Nope, thats it. You will probably want to put new bearings in the diff while its apart though. Unless you have low miles. I was going to suggest gears aswell but from your sig im gonna assume you planned to anyway.

 

Thanks man, yeah D'agostino Racing has a great deal on rear ends packages. Going to get a new 8.8 with traction loc and axles all in 31 spline with 3.73 gears that I already have.

 

Dont forget to get it assembled properly with the correct backlash and the right gear pattern.

 

Im kinda new to mustangs so what do you mean correct backlash?