28 spline axle tube is 2.75" diameter
31 spline axle tube is 3.25" diameter
The carriers are the same, interestingly enough -- they use the same bearings between the carrier and housing as well. But the spider gears the axle shafts go into are obviously different.
The outboard axle bearings are different. 31 spline are 2.5" in diameter, 28 spline are 2.25" diameter -- obviously the 31 spline won't fit in 28 spline axle tubes. Needless to say they are different in their internal diameters as well.
I posted all this before, by the way, in my topics on my 31 spline buildup.
The centersection of a 31 spline axle is physically larger and beefier as well.
Both 28 and 31 spline can use the same ring and pinion sets.
Both have the ABS pickup mounted the same way.
There is information on Explorer axle conversion on http://www.therangerstation.com
and other spots as well. I know The Ranger Station has some tech stuff for sure.
Yeah, take a look here: http://www.therangerstation.com/tech...plorer8_8.html
This is someone else doing what I did, more or less:
And these are my posts here:
And I put info on this topic as well:
Search and ye shall find!