Okay, I'm no expert but this is my idea. Axles come in different sizes which is normally measured by the number of splines they have. For instance, an early bronco came with 28 spline shafts in it's 9". However, some 9" for F150's and such came with larger, 31 spline shafts.
Looks like your spool is the wrong size for your axles.
Are you saying that on each side gear the splines are not evenly spaced all the way around the inside? Is there a spline missing or something? I never heard of an "idiot spline" in 9" rear side gears...
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