My fox is in big need of a new tranny and differential, only problem is, the differential i need is 31 spline and the tranny i need is input 10 output 28. Am i going to need to spend some extra money to get the right ones? As it is im looking at 2k for both and cant really soend much more than that. Is there a sight that has better options? Ive looked on american muscle, lmr, and cjpony parts and they all have the same, 28 tranny and 31 diff, but that doesnt make sense because it wont work.
The transmission splines in no way affect the differential splines. The input splines on the trans only require you to match the correct clutch disc to them. The transmission output splines are matched to the driveshaft slip yoke, not the differential. The differential splines are the ones on the axles themselves. The axles need to be correct for the carrier inside the differential.
Why don't you tell us what transmission you have and where you got your numbers from.
You may just be over complicating a very simple situation, there are only a few manual transmissions that will work in these cars, most of which are t5's.
An 03 cobra carrier is 31 spline, can be had new for $250 or less. (if that is in fact a question you were asking). Just realize it will not work with 28 spline axles (stock size).