Imp I thought of you when I posted, I recall you post good knowledge and experience with gears. Yes the center sections have to be dropped for repairs/mods. I have never set gears before, which is why I would like an extra set to have in the shop, assuming it's going to take some time for me to complete.
@drdoom
Doc, I learned the hard way by ruining a brand new set of 4.57s, after having set up maybe 10 or more previously. Simplest of mistakes due to lack of enough knowledge, the 9-inch Ford has big, round threaded spacers which encircle the outer races of the differential support roller bearings. Some of the "Integral" designs of center sections have them also, but 8.8 Ford does not, relying on shims beneath the bearings. The 9-inch design made cake of the job of locating the ring gear in the right place, while at the same time applying the proper pre-load". My mistake was to not know those threaded rings were movable after the cap bolts were tightened. Tip-off should have been the little "keepers" which bolted on top of the caps, and entered holes around the adjustment rings. I had mis-threaded one, then torqued down the caps. Trying this baby out, not even a block from home, horrible, loud, frightening, screaming whine! No cover plate, center section has to come out to inspect. The gear teeth were incredibly scored. I set these things up hit and miss, meaning assemble, check tooth contact pattern, then adjust as necessary. Sometimes took a number of tries. That's what you get lacking the correct specialized tools to set up hypoid gears.
Your 2005 (?) has a rear 8.8". Unusual in that case is aluminum alloy, less indestructible that nodular cast iron. (assuming 4th. Gen. same as 3rd.). Someone correct me if not, please! Generally, the end of the pinion gear has painted on numbers, indicating the pinion depth location, measured from some reference surface, usually the gasket surface for the cover plate. Those numbers must be used along with your particular pumpkin to determine pinion shim thickness for location purposes. Then comes pinion bearing preload, most often achieved through use of a "crush sleeve" which takes up several thousand pounds of pinion flange nut tightening (thread tension) force. Since pinion brg. preload is just about the most important consideration in successful set-up, the biggies like High-Performance options use(d) a SOLID bearing spacer, which is located between the two bearing roller/cone assemblies. Much more reliable than the crush-sleeve but far trickier to do. Crush-sleeve introduces possible error due to incorrect torque of nut being obtained, result can be either too loose bearings (BAD), or too tight (bad, but works, running too hot).
Finally, "backlash", clearance between ring and pinion teeth, measured at the outer periphery of the ring, called out as rotational clearance with pinion held stationary, usually never less than 0.010". Backlash also affects tooth contact pattern, so all these factors play into one-another. When in doubt, more lash is better than too little, and contact pattern on "Drive" teeth of ring can be slightly off-center towards the inside diameter, if necessary to obtain good lash.
Oh, yeah, almost forgot. Drive tooth face rises upwards from ring gear at nearly a right-angle. Very important as "Drive" always sees far more torque than "Coast" teeth, which rise up at a much shallower angle, that contributing to "spreading" forces pushing the gears apart during operation. Now, the final "kick": Typically, 4X4s take a regular rear-use pumpkin, turn it around, and mount it up front. GREAT! Now you have the "Coast" teeth DRIVING the front axles! Somewhere, decades ago, on an F-Series, I spotted the front pumpkin mounted UPSIDE-DOWN! From FORD! That put the teeth in proper perspective for forward driving. Robbed the "drowning-bath" of oil from the pinion bearings, though. Later, the "fix" became "special" gearsets cut in reverse, which allowed normal (pinion at bottom) mounting. Beware of the pitfall of reverse cut gears! imp
