9" Ford spline vs. strength question
 

I have a 74 Camaro that I am looking at swapping the rearend. How much difference does spline numbers make in strength on a Ford 9"? This car has about 550 hp small block. If I change spool and axles later, will different spline axles fit the housing?

you can get almost any " axle gear " spline in the locker, 28, 31, 35
the 28 is most commen, the cup cars use 31, the housing will fit any

with more splines on the axle the axle has to be a larger diameter, which gives more strength to the axle. Ford I beleive has 28 spline and 31 in their more performance oriented cars.
For aftermarket axles, the housing will take up to 40 spline axles, but you need the matching spool.
To run a 35 or 40 spline spool in a ford, the carrier has to be able to use 3.25 bearings.
The weak point in a ford 9" is the pinion support tends to break. The N case is a little stronger, but if you intend to put a lot of hp and torque through it, get an aftermarket carrier