by Shdwdrgn » Mon Jun 02, 2014 2:55 pm
My limited experience is that the rear axle size is stamped into the cover. Both the original 8.0 and the new 8.6 had it stamped in, but I had to clean up the rust to actually see them. If you're changing things anyway, by far the easiest option is to get an axle that already has the gears you want... a few hours of labor and you can swap the rear axle by yourself.
You lose nothing by swapping from the 8.0 to the 8.6 rear. As far as I could tell, the difference in diameter was placed *above* the axle line, so you have exactly the same ground clearance. I have no experience with the 9.5.
Expect the front diff to be a multi-day project. If you have experienced help, it might not be, but expect it anyway! Also since everything will be apart anyway, you might as well inspect and re-lube your disconnect.
You have an advantage when it comes to reprogramming the gearing in your PCM -- tuners like HPT have the info available to make the change. Those of us with the older PCM aren't so lucky. However does anyone know if the newer models are still limited to stock gear ratios in the PCM, or if the 4.56's can indeed be programmed in?
GT5/G80, 265/70-16, PCMforLess + personal tuning, quad headlights
Self-made steel front bumper / pushbar / skid / CAI / lightbar